MATERIALS TRANSACTIONS
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ONLINE ISSN: 1347-5320
PRINT ISSN: 1345-9678

MATERIALS TRANSACTIONS Vol. 56 (2015), No. 9

  • PREFACE

    pp. 1315-1315

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    DOI:10.2320/matertrans.MPR2015904

  • Magnetocaloric Effect in La0.7Ca0.25Ba0.05MnO3 Nanocrystals Exhibiting the Crossover of First- and Second-Order Magnetic Phase Transformation

    pp. 1316-1319

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    DOI:10.2320/matertrans.MA201546

    In this work, we present a detailed study on the magnetocaloric effect near the first-to-second order magnetic phase transformation of La0.7Ca0.25Ba0.05MnO3 nanoparticles with averaged crystallite sizes D = 39–79 nm. The ferromagnetic-paramagnetic phase-transition region of the bulk sample (exhibiting the first-order nature) becomes more broadened in nanoparticles (exhibiting the second-order nature). Based on isothermal magnetization data, M(H), we calculated magnetic entropy change versus temperature, ΔSm(T), of the samples under magnetic-field changes ΔH = 0–30 kOe. As a result, |ΔSm| reaches the maximum value (|ΔSmax|) around TC = 258–262 K. With ΔH = 30 kOe, |ΔSmax| values obtained from the samples are located in the range 4.38–5.63 J·kg−1·K−1, corresponding to refrigerant-capacity values RC = 138–141 J·kg−1. Field dependences of |ΔSmax| and RC can be expressed by a power law, with |ΔSmax| = a·Hn and RC = b·HN. Interestingly, all the ΔSm(T) curves of the samples undergoing the second-order phase transition at different applied fields are collapsed onto a universal curve, which is obtained by normalizing the ΔSm(T, H) curves to their respective ΔSmax value, and rescaling the temperature axis above and below TC with θ = (TTC)/(TrTC), where Tr is the reference temperature.
  • First Order Magnetization Process in Polycrystalline Perovskite Manganite

    pp. 1320-1322

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    DOI:10.2320/matertrans.MA201507

    The Ising spin model with random competing ferromagnetic, antiferromagnetic exchange interactions in the external field is used to investigate the First Order Magnetization Process at low temperature in doped polycrystalline magnetic perovskite Pr0.5Ca0.5Mn1−xMxO3 (M = Co, Ga). Using Callen identity in the correlated effective field approximation, our calculation describes well the experimental behavior, which is explained by the reorientation of antiferromagnetic clusters and by the expansion of ferromagnetic clusters in the external field at low temperature. The origin of the number of critical fields at which the steps of magnetization occurred, the magnitude of these steps and the related jumps in the magnetic field dependent resistivity are also discussed.
  • Spin-Transfer Torque Switching at Ultra Low Current Densities

    pp. 1323-1326

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    DOI:10.2320/matertrans.MA201570

    The influence of the tantalum buffer layer on the magnetic anisotropy of perpendicular Co-Fe-B/MgO based magnetic tunnel junctions is studied using magneto-optical Kerr-spectroscopy. Samples without a tantalum buffer are found to exhibit no perpendicular magnetization. The transport of boron into the tantalum buffer is considered to play an important role on the switching currents of those devices. With the optimized layer stack of a perpendicular tunnel junction, a minimal critical switching current density of only 9.3 kA/cm2 is observed and the thermally activated switching probability distribution is discussed.
  • Magnetic Behaviors of Arrays of Co-Ni-P Nanorod: Effects of Applied Magnetic Field

    pp. 1327-1330

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    DOI:10.2320/matertrans.MA201520

    The Co-Ni-P nanorods were fabricated by electrodeposition method by using the porous polycarbonate template. The investigation by mean of X-ray diffraction and high-resolution transmission electron microscopy indicated that samples were nanocrystalline clusters embedded in the amorphous base. The samples exhibited a room temperature ferromagnetism with the high magnetic anisotropy along the rod. The applied magnetic fields during the fabrication of the Co-Ni-P nanorods was strongly influenced by the magnetic properties. The MR/MS ratio and coercivity rapidly increased when the magnetic applied field changed from 0 to 0.21 T.
  • Critical Behavior of La0.7Ca0.3MnO3 Nanoparticles

    pp. 1331-1334

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    DOI:10.2320/matertrans.MA201552

    We used the modified Arrott plot method to analyze magnetic-field dependences of magnetization, M(H), around the ferromagnetic-paramagnetic (FM-PM) phase-transition temperature (TC) of three nanocrystalline La0.7Ca0.3MnO3 samples with average crystallite sizes d = 40, 23, and 16 nm. The analyses obtained the values of critical parameters to be TC ≈ 261 K, β = 0.485 ± 0.005, γ = 1.051 ± 0.094 and δ = 3.1 ± 0.1 for the sample with d = 40 nm, TC ≈ 252 K, β = 0.525 ± 0.010, γ = 0.893 ± 0.139 and δ = 2.7 ± 0.1 for d = 23 nm, and TC ≈ 236 K, β = 0.621 ± 0.008, γ = 0.825 ± 0.007 and δ = 2.2 ± 0.2 for d = 16 nm. With these critical values, the M(H) data points around TC of the samples fall into two universal branches of a scaling function M(H, ε) = |ε|βf±(H/|ε|β+γ), with ε = (TTC)/TC, f+ for T > TC and f for T < TC. The results reveal that the crystallite-size reduction of nanoparticles decreases the TC value. This is ascribed to the decrease of FM double-exchange interactions between Mn3+ and Mn4+ ions, which is related to the β change from 0.485 for d = 40 nm to 0.621 for d = 16 nm, corresponding to the change in FM order from the long-range type to the short-range one.
  • Effect of Cerium Doping on Crystal Structure and Magnetic Properties of La1−yCeyFe11.44Si1.56 Compounds

    pp. 1335-1338

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    DOI:10.2320/matertrans.MA201518

    Crystal structure and magnetic properties of Cerium-doped La1−yCeyFe11.44Si1.56 (y = 0.0 − 0.3) compounds are reported. The compounds possess the NaZn13-type cubic structure with ferromagnetic arrangement. The substitution of Ce into the host lattice slightly decreased the lattice constant from 1.1477 to 1.1471 Å, and as the doping content increased, the saturation magnetization and Curie temperature of the samples were also reduced. A large value of the magnetic entropy change ΔSm was observed at low doping concentration.
  • Room-Temperature Ferromagnetism in Nickel-Doped Wide Band Gap Ferroelectric Bi0.5K0.5TiO3 Nanocrystals

    pp. 1339-1343

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    DOI:10.2320/matertrans.MA201548

    We report the effect of nickel doping on the structural, optical, and magnetic properties of Bi0.5K0.5TiO3 nanocrystal. The X-ray diffraction results indicated that Ni was substituted into the Ti sites in Bi0.5K0.5TiO3 and the NiTiO3 phase was formed when Ni concentration was higher than 3 mol%. The band gap value decreased from 3.31 eV to 2.96 eV when the Ni concentration changed from 0 to 3 mol% and then increased with higher Ni concentration. Both weak-ferromagnetism and diamagnetism coexisted in un-doped Bi0.5K0.5TiO3 samples. The ferromagnetic signal strongly influenced the paramagnetic signal for Ni-doped Bi0.5K0.5TiO3 samples at room temperature. The room-temperature ferromagnetism in Ni-doped Bi0.5K0.5TiO3 samples could be contributed by intrinsic reason due to presence of Ni ion in Bi0.5K0.5TiO3 crystal and by extrinsic reason due to segregation of NiTiO3 clusters when Ni concentration was over 3 mol% threshold. This method may provide a useful way to get both single-phase multiferroics and composite multiferroics materials.
  • Atomistic Analyses of Competition between Site-Selective Segregation and Association of Point Defects at Grain Boundary in Y2O3-Doped ZrO2

    pp. 1344-1349

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    DOI:10.2320/matertrans.MA201567

    The site-selective occupation of point defects, Y3+ ions (Y′Zr) and O2− vacancies (V\ddot{O}), and their associations at a symmetric tilt grain boundary (GB) are studied to understand their competitive contribution to energetically favorable atomic arrangements by using atomistic simulations. It is found that at the GB there are the favorable sites for segregation of an isolated Y′Zr and V\ddot{O}. This indicates that the driving force for the site-selective segregation is present. Moreover, our results of Y′Zr-V\ddot{O} association at the GB show that the lattice energies are very dispersed despite that a second-nearest neighbor (SNN) vacancy to Y′Zr is favored for bulk Y2O3-doped ZrO2. The result suggests that the site-selective segregation has significant effects on the favorable point defect arrangement at the GB core, competing with the point defect associations. For more realistic cases, Monte Carlo simulations are performed to reveal favorable atomic arrangements for a high dopant concentration, where point defects are crowded at the GB. The results show that the region of GB segregation can be classified with respect to O2− coordination to cation species; at the GB core the favorable configuration is not necessarily a SNN O2− vacancy relative to Y3+. On the other hand, eight-fold O2− coordination is sustained for Y3+ ions more than ∼3 Å distant from the GB plane. The difference in O2− coordination may play an important role in O2− ionic conductivity at GBs via the energetics for O2− migration.
  • Stability of 12CaO·7Al2O3 Crystal under High-Pressure: Experimental and First-Principles Approaches

    pp. 1350-1353

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    DOI:10.2320/matertrans.MA201575

    Stability of 12CaO·7Al2O3 (C12A7) crystal under high-pressure conditions is investigated by sample recovery experiments and first-principles calculations. After high-pressure and high-temperature treatments, C12A7 crystal is mainly decomposed to 2CaO·Al2O3 (C2A) and 4CaO·3Al2O3 (C4A3). According to first-principles calculations, the volume of C12A7 crystal is larger than that of [4(C2A)+C4A3]. From energetic point of view, C12A7 is stable at 0 GPa but it becomes unstable as pressure increases. This is caused by large volume of C12A7 at 0 GPa while the contribution of volume shrink of each substance is rather small. This indicated that the volume at 0 GPa is a dominant factor in these systems under high-pressure.
  • Ni2O3 Decoration of WO3 Thin Film for High Sensitivity NH3 Gas Sensor

    pp. 1354-1357

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    DOI:10.2320/matertrans.MA201572

    A facile method for fabricating thin films of granular tungsten oxide (WO3) particles decorated with nickel oxide (Ni2O3) nanoparticles was developed for high response NH3 gas sensor. The WO3 granular film was fabricated by sputter deposition of tungsten, followed by oxidation. Ni2O3 nanoparticles were deposited onto the WO3 film by arc-discharge deposition of single-wall carbon nanotubes (SWCNTs) with Ni catalyst nanowires, followed by burning the carbon nanotubes. The Ni nanoparticle catalysts deposited on the SWCNTs were then oxidized to Ni2O3. The Ni2O3 nanoparticles on the surface exhibited a catalytic role in ammonia gas reactions. A maximum response of 13.5 at operating temperature of 250°C to 200 ppm NH3 gas concentration was found. In addition, the gas sensing mechanism of Ni2O3 decorated WO3 film was also discussed in this study.
  • Physical Properties of Sol-Gel Lead Nickel Titanate Powder Pb(Ti1−xNix)O3

    pp. 1358-1361

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    DOI:10.2320/matertrans.MA201508

    A series of sol-gel lead nickel titanate powder with composition of PbTi1−xNixO3, where x = 0.00, 0.03, 0.06, 0.08, 0.10 and 0.12, were studied using X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy, and magnetization (M-H) curves. XRD patterns show that PbTi1−xNixO3 materials well crystallize in tetragonal phase. The tetragonal distorted ratio c/a of PbTi1−xNixO3 was found to decrease with the increase of Ni content and to increase with increasing calcining temperature. The mean size of PbTi1−xNixO3 crystal particles gradually decreased with increasing Ni content. Some Raman modes shifted to lower wavenumbers when Ni content increases, that is assigned to the variation of crystal structure due to the incorporation of Ni into PbTiO3 crystal. In addition, the results of room temperature magnetization measurements present an obvious improvement of ferromagnetism when Ni content increases in the range from 3 to 12 mol%.
  • Large Electrical Resistance Variation at Low Temperature in Transition Metal-Doped Ge Single Crystals

    pp. 1362-1364

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    DOI:10.2320/matertrans.MA201571

    We have grown un-doped and transition metal (V, Cr, Mn, Fe, Co, Ni, Cu)-doped Ge bulk single crystals using the vertical gradient solidification method. The electrical resistivities of V, Ni, Co, and Fe-doped Ge crystals significantly increased, 104∼105 times, between 5 and 100 K, which were 100 times larger than that of the commercial Ge resistance temperature device (RTD). The large variation of electrical resistance at low temperature arises from decreased carrier density and mobility at low temperature. The mobility reduction at low temperature might be caused by ionized impurity scattering.
  • Investigation of the Influence of Singly and Dually Doping Effect on Scattering Mechanisms and Thermoelectric Properties of Perovskite-Type STO

    pp. 1365-1369

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    DOI:10.2320/matertrans.MA201512

    This paper presents a systematic investigation of typical characterizations of Sr(1-1.5x-0.5y)DyxTi1-yNbyO3 composition based on single Nb- and Dy-doped as well as Nb/Dy co-doped SrTiO3. Nb concentration of 10, 13, 17, 20 and 24 at% and Dy concentration of 4, 8, 10, and 13 at% were used for different doping compounds. XRD data was used to calculate the lattice constants. The limit of solubility of doped element in host lattice was determined based on the graph showing the dependence of lattice parameters on doping concentration. The thermoelectric properties were investigated from 20 to 1000°C or 293 to 1273 K. The electrical conductivity increases below 600 K but decreases above 600 K with increasing doping content for all cases. This characterization reached about 900 S/cm at 570 K with 4% dysprosium and 20% niobium doped in STO. Both the electrical and thermal conductivity of single Nb-doped samples increase with increasing Nb content. In contrast, the thermal conductivity of single Dy doping decreases with increasing Dy content and consequently best absolute values of Seebeck coefficient. Generally, increasing doping concentration provides larger magnitude of Seebeck coefficient for all cases of doping. The best magnitude of the figure of merit reaches approximately 0.17 at 1273 K. The optimized composition should comprise quaternary compounds of which is Sr0.84Dy0.04Ti0.80Nb0.2O3, especially for fast cooling regime.
  • Ferroelectric and Piezoelectric Properties of Lead-Free BCT-xBZT Solid Solutions

    pp. 1370-1373

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    DOI:10.2320/matertrans.MA201511

    Lead-free BCT-xBZT solid solutions were prepared by the conventional solid-state reaction route. A full set of elastic, piezoelectric, and dielectric parameters were measured using a resonance method and calculated following the formulae in the IEEE standard for piezoelectric ceramics. In addition, ferroelectric properties were also investigated to demonstrate the “softening” and the diffuse transitions in the material.
  • Dielectric Relaxation of Ba1−xCaxTiO3 (x = 0.0–0.3)

    pp. 1374-1377

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    DOI:10.2320/matertrans.MA201543

    Ba1−xCaxTiO3 samples (x = 0.0–0.30) were prepared by a solid state reaction method. X-ray diffraction patterns of the prepared samples show that the samples containing Ca2+ concentration lower than 14 at% were identified to tetragonal phase of BaTiO3. In the samples with Ca2+ concentration higher than 14 at% CaTiO3 appears and coexists with BaTiO3. The dielectric constant at room temperature of all the samples was measured in a frequency range from zero to 2.5 MHz. A modified Cole-Cole formula was used to fit the experimental data. The fitting results show that the samples exhibit a single relaxation process that suggests BaTiO3 and CaTiO3 coexist in a nested hybrid form in the samples with Ca concentration in a range of (0.14–0.30). An abnormal dependence on the Ca2+ concentration of the dielectric relaxation time was observed and supposed to be related with a pinning effect due to the local point-deformation caused by Ca2+ substitution and/or with a nesting of BaTiO3 and CaTiO3 in a hybrid form.
  • Microstructural and Ferroelectric Properties of Bi0.5(Na,K)0.5TiO3-Based Modified by Bi0.5Li0.5TiO3 Lead-Free Piezoelectric Ceramics

    pp. 1378-1382

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    DOI:10.2320/matertrans.MA201553

    Lead-free ceramics of composition (0.97 − x)Bi0.5Na0.4K0.1TiO3-0.03BiAlO3-xBi0.5Li0.5TiO3 (BNKTBA-xBLTO) were synthesized using solid state technique. The strong enhancements in ferroelectric and electric-field-induced strain were obtained. The electric-field-induced strain values were increased from 410 pm/V to 688 pm/V for 6 mol% BLTO-added which results from the phase transition from rhombohedral to tetragonal structure. The maximum spontaneous polarization increased from 26.5 µC/cm2 to 30.8 µC/cm2 for 4 mol% BLTO solid solution in BNKTBA and then decreased as BLTO was further added. We expect that this work could be helpful for further understanding the original enhancement in electrical field-induced strain in lead-free BNKT-based ceramics due to comparison between A- and B-site co-modifications.
  • Stable Gold Carbide Nanostructures

    pp. 1383-1386

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    DOI:10.2320/matertrans.MA201530

    The exemplars of gold carbide AuC in cubic F-43m structure and cluster form Au6C3 are reported. The characteristics of structures were obtained on basis of Time-Dependent Density Functional Theory (TD-DFT) embedded within the framework of Generalized Gradient Approximation (GGA) and utilized Pardew-Burke-Ernzerhof functional (PBE) and spin-polarized wave functions. We found that the modeled forms of gold carbide exhibited no ferromagnetism while maintaining metallic ground state. The calculation showed the dominance of optical transitions which preserved spin.
  • Flexible and Transparent Conducting ZZO/Ag/ZZO Multilayer Grown by Sputtering at Room Temperature

    pp. 1387-1389

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    DOI:10.2320/matertrans.MA201501

    We studied the optical, electrical, and structural properties of indium-free Zr-doped ZnO (ZZO)/Ag/ZZO multilayers prepared on poly(ether sulfone) (PES) substrates by RF magnetron sputtering at room temperature. The optical and electrical characteristics of the crystalline ZZO/Ag/ZZO multilayer electrodes can be improved by the insertion of a nano-sized Ag interlayer with an optimized thickness between top and bottom ZZO films, owing to the very low resistivity. The ZZO/Ag (12 nm)/ZZO/PES exhibited high transmittance of ∼85.6% in the wavelength range from 450 to 600 nm and a low resistivity of ∼6 × 10−5 Ω·cm. Additionally, X-ray photoelectron spectroscopy (XPS) investigations for the ZZO/Ag/ZZO multilayers confirmed no interfacial reaction between the ZZO and Ag films. The performances indicate that the indium-free ZZO/Ag/ZZO multilayers are promising as transparent conducting films for low-cost flexible optoelectronics applications.
  • Molecular Dynamics Simulations of the Nucleotides and Metallic Nanoparticles Interaction on a Carbon Nanotube Matrix

    pp. 1390-1393

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    DOI:10.2320/matertrans.MA201565

    We simulated the interaction of the small nucleotide chain (NC) with gold nanoparticles (NPs) inside carbon nanotube (CNT) of an open ended boundary. Such system represents a great interest in many aspects of today biochemical and nanotechnological research (diagnostic applications, drug delivery in cell, nanorobotic design and related manipulations). The entire system (the NC chain, gold NPs and CNT) were allowed to interact with each other by the Van der Waals (VdW) forces only. The CNT was described through a quantum-chemistry potential, though the trajectory calculation for the whole NC-NP-CNT model was performed via the classical molecular dynamics (MD) approach. The Lennard-Jones short-ranged interaction is assumed between the NC, NP and CNT. We have carried out a series of MD simulations on different NC-NP-CNT configurations to investigate the pequliarities of NC-NP bonding and structural formation along with dynamical behavior inside a CNT matrix under rather a weak VdW interaction.
  • Fabrication of Mn-Bi Nanoparticles by High Energy Ball Milling

    pp. 1394-1398

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    DOI:10.2320/matertrans.MA201577

    The MnBi low temperature phase with high value and positive temperature coefficient of its coercivity has a potential for production of both the nanocomposite and hybrid permanent magnets. In this report, we present our results of investigation of fabrication of Mn55Bi45 nanoparticles by using high energy ball milling method. The Mn55Bi45 alloy was first arc-melted and then ball-milled for various time of 0.25–8 h in different environments of Argon, Alcohol, Petrol and Xylene. The resulted powder was subsequently annealed at temperatures of 200 and 250°C for time periods of 0.5–4 h in Ar gas. The fraction of the MnBi low temperature phase and the size of the particles strongly depend on the fabrication conditions. The desired MnBi nanoparticles with size of 25–100 nm and coercivity μ0Hc > 1 T can be achieved by choosing appropriate fabrication conditions.
  • Pt- and Ag-Decorated Carbon Nanotube Network Layers for Enhanced NH3 Gas Sensitivity at Room Temperature

    pp. 1399-1402

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    DOI:10.2320/matertrans.MA201538

    Multi-walled carbon nanotubes (CNTs) were directly grown on alumina substrates patterned with Pt interdigitated electrodes by chemical vapor deposition method to fabricate gas sensor. Pt and Ag thin layers with nominal thicknesses of 2 and 4 nm were coated on the CNT layer by evaporation method to modify the CNT properties. The gas sensing results showed that the CNT/Pt- and CNT/Ag-based sensors exhibited enhanced sensitivity to NH3 gas at room temperature. The responses of the CNT/Pt (3.0%) and CNT/Ag (6.9%) sensors with a 4 nm thick metallic layer to 70 ppm NH3 were higher than that of pristine CNT sensor (1.5%).
  • Kinetics of CO Oxidation over Pt-Modified CuO Nanocatalysts

    pp. 1403-1407

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    DOI:10.2320/matertrans.MA201545

    Three Pt-CuO nanocatalysts PtCu/Al, PtCu/CeAl and PtCu/Ce have been successfully prepared. The characterization of the catalysts was examined by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), X-ray energy dispersive analysis (EDS), temperature-programmed reduction (TPR), nitrogen physisorption measurements, and IR-CO adsorption. The kinetics of CO oxidation using these catalysts was studied in a gradientless flow-circulating system at 398–498 K. The obtained kinetic equation confirmed that the reaction proceeds in medium surface coverage with the participation of CO molecules and oxygen atoms.
  • The Dependence of a Quantum Acoustoelectric Current on Some Qualities in a Cylindrical Quantum Wire with an Infinite Potential GaAs/GaAsAl

    pp. 1408-1411

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    DOI:10.2320/matertrans.MA201514

    The quantum acoustoelectric (QAE) current is studied by a quantum kinetic equation method and we obtain analytic expression for QAE in a cylindrical quantum wire with an infinite potential (CQWIP) GaAs/GaAsAl. The computational results show that the dependence of the QAE current on the radius of CQWIP GaAs/GaAsAl, the Fermi energy εF and temperature T is non-monotonic, and the appearance of peak when the condition ω q = ω k + ћ2(B2n’,N - B2n,N) / 2mR2 (nn’ and NN’) is satisfied. Our result indicates that the dominant mechanism for such a behavior is the electron confinement in the CQWIP GaAs/GaAsAl and transitions between mini-bands. All these results are compared with those for normal bulk semiconductors and superlattice to show the differences. The dependence of a QAE current on some qualities in a CQWIP GaAs/GaAsAl is newly developed.
  • Crystal Structure and Photoluminescence Properties of Eu-Doped Y2O3 Nanoparticles Prepared by Mechanical Milling

    pp. 1412-1415

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    DOI:10.2320/matertrans.MA201556

    We have used a top-down approach of the mechanical milling to fabricate Y2O3:Eu3+ nanoparticles (NPs), and then studied their crystal structure and photoluminescence (PL) properties based on X-ray diffraction (XRD), electron paramagnetic resonance (EPR) and PL spectroscopy. XRD results revealed that the change of the milling time (tm) from 0 to 540 minutes (min) decreased the average crystallite size (d) of NPs from ∼83 nm (for tm = 0 min) to below 3.5 nm (for tm = 540 min). This varied lattice strain and defects, and caused the structural changes, which influenced directly the PL properties of NPs. Among the fabricated NP samples, those with tm = 5–10 min (corresponding to d ≈ 25–40 nm) offer strongest PL intensity at ∼611 nm (due to the electronic transition 5D07F2). The increase of the longer milling time (i.e., lowering d) reduces quickly the intensity of this emission, but slightly increased the intensity of auxiliary emissions. The nature of the observed phenomena was discussed.
  • Judd–Ofelt Analysis of Eu3+ Emission in TiO2 Anatase Nanoparticles

    pp. 1416-1418

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    DOI:10.2320/matertrans.MA201566

    Preparation and spectroscopic studies of the TiO2 nanopowders doped with Eu3+ ions are described. Efficient emission in the red part of the visible spectrum can be obtained due to the 5D07F2 emission of europium ions. Quantum efficiency of such emission was estimated to be about 0.83, which indicates a rather weak role of the non-radiative losses. However, the increase of Eu3+ concentration up to 10 at% significantly lowers the quantum efficiency because of the energy transfer and re-absorption processes. Higher doping concentrations (larger than 3 at% of Eu3+) also decrease the covalency of the Eu3+–O2− chemical bonds.
  • Luminescence Properties of Ce/Tb/Sm Co-Doped Tellurite Glass for White Leds Application

    pp. 1419-1421

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    DOI:10.2320/matertrans.MA201509

    In this work, the Ce/Tb/Sm doped glasses with the composition of TeO2-B2O3-ZnO-Na2O were synthesized by melt quenching process. The photoluminescence properties of glasses doped with Ce3+, Tb3+ and Sm3+ single, doubly and triply doped TeO2-B2O3-ZnO-Na2O (TBZN) were studied by mean of emission and excitation spectra. There was an overlap between Ce3+ emission and Tb3+, Sm3+ absorption in the wavelength range of 350–500 nm. Therefore, it was expected that an efficient energy transfer occurred from Ce3+ to Tb3+ and Ce3+ to Sm3+ ions. When excited by ultraviolet wavelengths the co-doped glasses emit a combination of blue, green and red orange forming white light.
  • Synthesis and Optical Characterization of Samarium Doped Lanthanum Orthophosphate Nanowires

    pp. 1422-1424

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    DOI:10.2320/matertrans.MA201526

    LaPO4 nanowires doped with 0, 1, 2, 3, 4 and 5 mol% Sm3+ were prepared by co-precipitation technique. These nanowires were studied by X-ray diffraction (XRD), transmission electron microscopy (TEM), photoluminescence (PL), photoluminescence excitation (PLE) spectra and energy-dispersive X-ray spectra (EDS). The PL spectra exhibited 4 groups of emission peaks, which are assigned to the transitions from the excited state 4G5/2 to the ground states 6HJ with J = 5/2; 7/2; 9/2 and 11/2 of Sm3+ ions. The intensity of PL related to Sm3+ ion reached to a maximum when the Sm doping content was 2 mol%. The PLE spectra show 8 peaks, which are attributed to the absorption transitions from the 6H5/2 ground state to the 4K15/2, 4D3/2, 6P7/2, 4F7/2, 6P5/2, 4G9/2, 4I13/2 and 4I11/2 excited states.
  • Quantum Chemical Study of the 1:1 Complex between Ferrocene and Zinc Porphyrin, a Building-Block of Charge-Transfer Molecular Materials

    pp. 1425-1427

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    DOI:10.2320/matertrans.MA201561

    The molecular and electronic structure of the 1:1 charge-transfer complex between ferrocene (Fc) and zinc porphyrin (ZnP) are investigated with the aid of dispersion-corrected density functional theory (DFT) calculations. Four stable configurations were obtained, two with the Fc molecule laying on the ZnP plane and the other two where Fc interacts with the porphyrin’s perimeter. The dipole moment vectors of these Fc:ZnP complexes indicate that they are stabilized by the transfer of electronic charge density from Fc to ZnP or vice versa.
  • Fabrication of Solid Contact Ion Selective Electrode for Mercury (II) Using Conductive Polymer Membrane

    pp. 1428-1430

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    DOI:10.2320/matertrans.MA201562

    A solid-contact ion-selective electrode for mercury (II) ions was fabricated to determine Mercury (II) in aqueous environment. A conductive polymer membrane (polypyrrole-PPy) was synthesized electrochemically on paste carbon electrode, which is covered by the ion-selective membrane (ISM) — an important part of a complete solid contact ion selective electrode (SCISE). The electrode showed excellent potentiometric response over a wide concentration range from 10−9 M to 10−2 M and detection limit down to 6 × 10−10 M. A good selectivity towards Hg2+ ions in comparison with other common ions in water has also been observed. The electrode was employed for determination of Hg2+ in ballast water samples with high sensitivity and accuracy.
  • Sorting and Trapping Human Cells Using a Matrix of Square Micro-Magnets

    pp. 1431-1433

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    DOI:10.2320/matertrans.MA201563

    In this work we present a study on sorting and trapping some living human cells, including red blood cells (RBCs) and breast cancer cells (denoted T47D), by using patterned micro-magnets with dimensions of each micro-magnet 50 × 50 µm2. The diamagnetic properties of these cells and the force exerted on them along the z-axis have been investigated. The diamagnetic levitation height of each cell has been both theoretically calculated and experimentally studied. The results open a novel possibility for positioning living cells with further applications to medical diagnostics.
  • Magnetic Poly(Vinylsulfonic-co-Divinylbenzene) Catalysts for Direct Conversion of Cellulose into 5-Hydroxymethylfurfural Using Ionic Liquids

    pp. 1434-1440

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    DOI:10.2320/matertrans.MA201539

    Mesoporous poly(vinylsulfonic-co-divinylbenzene) (VS-DVB) and magnetic polymer (VS-DVB/CoFe2O4) are prepared and used as solid acidic catalysts to directly transform cellulose into 5-hydroxymethylfurfural (5-HMF). The characteristic and morphology of the polymers were examined by Fourier transformed infrared spectroscopy, X-ray diffraction, vibrating sample magnetometer, field-emission scanning microscope, and transmission electron microscopy. The yield of 5-HMF can reach as high as 98% from the dehydration of glucose using CrCl3·6H2O catalyst in tetrabutylammonium chloride at 120°C for 90 min. Cellulose conversion using the prepared VS-DVB in 1-butyl-3-methyl imidazolium chloride at 120°C for 180 min showed high yields of 50% glucose and 10% 5-HMF. An enhancement in 5-HMF yield was observed as reaction time increased. A combination of VS-DVB/CoFe2O4 and CrCl3·6H2O in ionic liquids was employed at optimal conditions for cellulose conversion. Magnetic catalysts were readily separated from resulting products in the magnetic field, as well as recycled and reused with negligible loss in activity. Glucose and 5-HMF yields were determined through high-performance liquid chromatography analysis.
  • Retrieval of Interatomic Separation from High-Order Harmonic Spectra Using the Electron Interference Effect

    pp. 1441-1444

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    DOI:10.2320/matertrans.MA201504

    A new method of extracting interatomic separation of CO2 is proposed based on using the dipole moment extracted from high-order harmonic generation (HHG) spectra. For this method, we show that the Bragg’s equations related to the electron interference effect can be obtained from the zero-points of the dipole moment. Using not only HHG with parallel polarization but also HHG with perpendicular one we discover an error-compensation effect which means that the errors of interatomic separation extracted from the two components of dipole moment are always opposite in the sign. Therefore, the final result of the interatomic separation obtained by the proposed method has a very high accuracy with the systematic error less than 1%.
  • In Situ Measurements of Work Function of Indium Tin Oxide after UV/Ozone Treatment

    pp. 1445-1447

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    DOI:10.2320/matertrans.MA201516

    In situ measurements of work function of indium tin oxide after UV/ozone treatment were carried out using a photoemission yield spectrometer with an open counter. Although the work function increased just after UV/ozone treatment, it decreased as time passed and finally returned to the initial value. The continuous change in work function with exposure to air was observed under dry atmosphere and at various temperatures. The returning process at higher temperature proceeded faster than at lower temperature. By contrast, humidity has no influence on the work function recovery. The exponential decay of work function was consistent with the first-order reaction rate equation. The rate constant obeyed Arrhenius’ equation, and the activation energy was estimated to be 22 kJ/mol.
  • Ab-Initio Multiplet Calculations of Fe-L2,3 X-ray Absorption Spectra in LiFePO4 and FePO4

    pp. 1448-1451

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    DOI:10.2320/matertrans.MA201573

    Soft X-ray absorption near-edge structures (XANES) at the L2,3-edges of transition metal has been widely used for investigating the chemical reactions during charge-discharge cycles in the cathode materials of lithium ion batteries. In order to extract the information about the electronic structures from the experimental results, however, a theoretical tool that can deal with the strong electronic correlations between 2p and 3d electrons is necessary. In this study, the ab-initio multiplet method based on the relativistic configuration interaction (CI) method has been applied to the calculations of Fe-L2,3 XANES of LiFePO4 and FePO4. Experimental XANES spectra were quantitatively reproduced by this method. The effects of local symmetries around Fe ions to the spectral shapes were also discussed.
  • First Principles Calculation of Thermal Expansion of Carbon and Boron Nitrides Based on Quasi-Harmonic Approximation

    pp. 1452-1456

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    DOI:10.2320/matertrans.MA201574

    We have performed theoretical analysis of thermal expansion of carbon and boron nitrides under finite temperature based on first principles phonon state calculations. Volume dependence of phonon density of states and thermodynamic functions such as heat capacity and vibrational free energy were theoretically examined. Through the volume dependence of vibrational free energy, thermal expansion at finite temperature is reproduced within quasi-harmonic approximation (QHA). Our calculation results have demonstrated that thermal expansion coefficients of typical ceramics materials (diamond, graphite, c-BN and h-BN) are reasonably well reproduced with the first principles approach employing QHA calculations.
  • Local Environment Analysis of Na Ions in β-Tricalcium Phosphate by X-ray Absorption Near-Edge Structure Measurements and First-Principles Calculations

    pp. 1457-1460

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    DOI:10.2320/matertrans.MA201578

    Na-incorporated β-tricalcium phosphate (β-TCP) was synthesized via the solid-state reaction method and a substitution mechanism for Na ions in the synthesized materials has been investigated by X-ray absorption near-edge structure (XANES) analysis. In addition, total electronic energy calculations within density functional theory were also carried out to obtain the most energetically favorable substitution site for Na ions in β-TCP. Both the spectroscopic and computational analysis indicate that substituted Na ions are likely to occupy Ca(4) site in β-TCP.
  • Interface Energies of Hetero- and Homo-Phase Boundaries and Their Impact on δ-γ Massive-Like Phase Transformations in Carbon Steel

    pp. 1461-1466

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    DOI:10.2320/matertrans.MA201568

    Systematic atomistic simulations of homo- and hetero-phase boundaries have been carried out to quantify interphase boundary energies in iron including δ-phase and γ-phase grain boundaries and δ/γ, δ/liquid and γ/liquid interfaces. Due to structural mismatch between body centered cubic (BCC) and face centered cubic (FCC) structures of the δ and γ phases, the minimum interface energy of the δ/γ interface is as high as 0.41 J/m2, much higher than the minimum interface energies of the δ/δ and γ/γ homo-phase interfaces, which are zero, suggesting that the high interface energy is one of the key factors that lead to the massive-like phase transformation from the δ phase to the γ phase observed by in situ radiography. Although the minimum δ/γ interface energy is not significantly higher than the δ/liquid interface energy that determines the δ nucleation upon solidification, it is yet high enough for the small entropy change upon the phase transformation to inhibit γ nucleation at a given critical radius until more than one orders of magnitude higher undercooling is achieved according to the classical theory of homogeneous nucleation.
  • Concurrent γ-Phase Nucleation as a Possible Mechanism of δ-γ Massive-like Phase Transformation in Carbon Steel: Numerical Analysis Based on Effective Interface Energy

    pp. 1467-1474

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    DOI:10.2320/matertrans.MA201569

    Effective interface energies of various homo- and hetero-interfaces of iron were calculated with an aid of phase-field modeling, taking into account geometric constraints by competition among grains or interfaces. Calculated effective interface energies for δ/γ, δ/δ, and γ/γ interfaces are 0.56, 0.44 and 0.37 J/m2, respectively. Using two simple geometric models for nucleation on or off an interface in the matrix, the optimal shape of a nucleus at a given radius and undercooling, a critical radius and an energy barrier for nucleation for each possible circumstance were numerically calculated. It is found that, although the energy barrier for γ-phase nucleation in homogeneous δ-phase matrix is more than three orders of magnitude greater than that for homogeneous solidification of δ-phase, the γ nucleation on a δ/δ grain boundary in the solidifying matrix suppresses the energy barrier, increasing a nucleation rate. Furthermore, it is found that the γ-phase nucleation on an existing γ nucleus halves undercooling needed with smaller critical radius. This suggests that, once γ nucleation is initiated, then following γ nucleation is promoted by doubled driving force, enabling multiple γ nucleation as in chain reaction. These findings are sufficient to explain experimentally observed phenomena during the δ-γ massive-like phase transformation even if other factors such as solute re-distribution or transformation is neglected.
  • Yet Another Marked Difference among Impurities as Modifier Elements for Refinement of Eutectic Si in Al-Si Alloys

    pp. 1475-1483

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    DOI:10.2320/matertrans.MA201576

    First principles calculations have been carried out in conjunction with lattice dynamics to evaluate free energies of ternary intermetallic phases, Al2Si2X (X = Ca, Sr, Ba, Eu, Y, Yb). The most stable crystal structure is identified for each X as a function of temperature. It is found that some of the intermetallic phases are stable over wide temperature range, thereby giving ability to modify and refine Al-Si eutectic phases with better mechanical properties. Substitution energy of the intermetallic phase is evaluated to aiming at examining the magnitude tolerance of the intermetallic phases with respect to deviation of chemical composition. Finally, the role of Al2Si2X as a modifier is examined from a solely geometric viewpoint, which provides yet another possible factors among many behind the X species dependence on modification of eutectic Si without using existing theories.
  • Magnetic Structure of Mn Films on Cu3Au(100) Revealed by Spin-Polarized Scanning Tunneling Microscopy

    pp. 1484-1487

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    DOI:10.2320/matertrans.MA201527

    It is shown that 21 monolayers of Manganese films grown on Cu3Au(100) at room temperature have an uncompensated layered antiferromagnetic structure that show a deviation from this configuration due to structural imperfections. In some areas of the film a p(2 × 2) magnetic super-structure was observed on the surface.
  • Simulation of the Magnetic Hysteresis Loop in Ferrimagnetism

    pp. 1488-1490

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    DOI:10.2320/matertrans.MAW201502

    Investigated the nano-scale Fe3O4 which is ferrimagnetic material that has attracted attention as an application of the spintronics. In order to investigate the magnetization process of Fe3O4 of ferrimagnetism, we report the results that derive the magnetic hysteresis loop with various parameter by the computer simulation using the retarded trace method.
  • Phase Transformation and Properties of Fe-Cr-Co Alloys with Low Cobalt Content

    pp. 1491-1495

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    DOI:10.2320/matertrans.M2015077

    The Curie temperature, phase transformation, microstructure and magnetic properties of Fe-10Cr-xCo alloys with low Cobalt content were analyzed after casted and solid solution quenched, respectively. The results show that the experimental Curie temperature increases from 1043 K to 1065 K with differential Co content addition, and which is about 50 K higher (as can be called “the degree of superheat”) compared with the calculated data. Besides, addition of Co promotes the formation of α-ferrite phase, and thus leads to the decrease of Vickers hardness. According to X-ray diffraction results, B2 type ordered structure forms, and Cr1.07Fe18.93 was observed in all the samples, whereas, CoFe15.7 only can be found in the sample with the addition of Co is more than 2 mass%.
  • Acoustic Emission Measurements on Metal-Hydrogenation Process by Using Electrochemical Charging Cell

    pp. 1496-1500

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    DOI:10.2320/matertrans.M2015169

    In a recent work, a hydrogenation process of palladium has been studied by the acoustic emission (AE) method with a new gas pressure cell. The high H2 gas pressure condition can, however, be easily provided by an electrochemical hydrogen charging technique. In this paper, characteristic AE power spectra caused by cavitation and/or bubble burst have been appraised by using an electrochemical separated AE cell. A typical AE signal induced by Pd hydride formation has been observed. The fundamental AE mode was 250 kHz in the Pd hydride formation stage, which was equal to the frequency measured by using the gas pressure cell as a standard hydrogenation technique.
  • Analysis of Non-Monotonic Temperature Behavior of the Coefficient of Thermal Expansion in Fe-Ni Alloys Studied by First-Principles Cluster Variation Method

    pp. 1501-1504

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    DOI:10.2320/matertrans.MAW201507

    Fe-Ni system has been attracting broad attentions as an Invar alloy. Although the origin of the Invar effects has been explained based on the temperature variation of alignments and magnitudes of magnetic moments, two of the present authors (YC and TM) reported that the non-monotonous temperature dependence of Coefficient of Thermal Expansion (CTE) were realized even without considering spin configurations explicitly. In the present study, we clarified that the main cause of the non-monotonous temperature dependence in CTE was atomic configuration effects which were originated from a peculiar concentration dependence of lattice constant in Fe-Ni system.
  • Evaluation of the Tensile Strength of Electron Beam Irradiated Powdered Ultra High Molecular Weight-Polyethylene (UHMWPE) Prior to Sintering

    pp. 1505-1508

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    DOI:10.2320/matertrans.M2015108

    We have studied the variation in tensile strength (σb), fracture strain (εf) and Young modulus (dσ/dε) of low voltage electron beam irradiation (HLEBI) on powdered ultra-high molecular weight-polyethylene from 0.043 to 0.43 MGy prior to sintering. The low dose of 0.043 MGy-HLEBI enhanced the σb, εf and dσ/dε, as well as increased the crystallinity ratio from 37 to 46% evaluated by differential scanning calorimetry (DSC). An additional dose apparently decreased the σb and εf, as well as the melting point from approximately 412 to 406 K and the crystallinity ratio from 46 to 43% for 0.043 to 0.43 MGy, respectively. Irradiation induces two competitive mechanisms, namely (i) the scission of chains and (ii) the crosslinking of chains. The discussion is focused on these mechanisms.
  • Ability of Hydroxyapatite Synthesized from Waste Oyster Shells to Remove Fluoride Ions

    pp. 1509-1512

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    DOI:10.2320/matertrans.M2015149

    Calcium carbonates, the main component of seashell waste, can be converted to hydroxyapatite (HA) via phosphate solution treatment. HA can remove F from water, as recommended by the World Health Organization (WHO), and HA particles of small sizes and/or large amounts are expected to remove F more effectively. To control the size and amount of synthesized HA, oyster shells were treated in the (NH4)2HPO4 solution whose pH value was adjusted to 10 at 4–120°C for 24 h. The HA particle size and amount increased with increasing reaction temperature. The samples’ abilities to remove F were evaluated by immersing them in F-containing solutions. The sample treated at 30°C removed F the most effectively, achieving a F concentration below 1.5 mg·dm−3, which is the level recommended by the WHO. The HA surface area is important in F removal.
  • Diffusivity and Solubility of Cu in a Reactor Pressure Vessel Steel Studied by Atom Probe Tomography

    pp. 1513-1516

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    DOI:10.2320/matertrans.M2015072

    The diffusivity and solubility limit of Cu in A533B steel, which is used in reactor pressure vessels, were studied by atom probe tomography (APT). Cu-A533B steel diffusion couples were annealed at temperatures of 550, 600, and 700°C, and the resulting Cu concentration profiles were measured. At the temperature of 700°C, the diffusivity of Cu in A533B steel was about 3 times higher than that in pure Fe, whereas at the temperature of 550°C, the diffusivity of Cu in A533B steel is almost closer to that in pure Fe. The solubility limit of Cu in A533B steel was similar to pure Fe. APT was also used to study the effect of the grain boundary (GB) diffusion. The results indicated that no Cu segregation occurred at GB near the Cu/A533B steel interface, which may imply that GB diffusion of Cu was not effective in A533B steel.
  • Effects of Homogeneous Low Energy Electron Beam Irradiation (HLEBI) on Adhesive Force of Peeling of Carbon Fiber Reinforced Epoxy Polymer (CFRP) and Polytetrafluoroethylene (PTFE)

    pp. 1517-1522

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    DOI:10.2320/matertrans.MAW201508

    The effects of homogeneous low energy (170 keV) electron beam irradiation (HLEBI) on the adhesion force indicated by peeling resistance (oFp) at each accumulative probability of peeling resistance (Pp) of laminated sheets of carbon fiber reinforced epoxy polymer (CFRP) and polytetrafluoroethylene (PTFE) were investigated. The slight detectable adhesive force of oFp before treatment were 0.3 and 7.6 Nm−1 at low and mid Pp of 0.06 and 0.50, respectively, since the intermolecular attractive force exists at PTFE and epoxy polymers at cross-linking zone. Although additional dose of HLEBI apparently reduced the oFp of laminated sheets irradiated at more than 0.30 MGy as usual radiation damages, small dose of 0.04 to 0.22 MGy-HLEBI increased the adhesive force of peeling (oFp) substantially over the untreated. 0.13 MGy-HLEBI enhanced the oFp up to the largest values of 9.8 and 44.0 Nm−1, respectively, which were more than 30.5 and 5.8 times larger than those before treatment. Based on the 3-parameter Weibull equation, the statistically lowest oFp value at Pp = 0 (Fs) was increased from zero to 9.2 Nm−1 by applying the 0.13 MGy HLEBI. XPS (X-ray photoelectron spectrometry) measurements detected the fluorine (1s) signal on peeled surface of CFRP side indicating the residual PTFE adhered well to the epoxy of CFRP by the HLEBI. Thus, the fracture probably propagated through the PTFE inside near cross-linking zone of interface. This is probably a result of adhesion force of PTFE/CFRP being made stronger than the cohesive force of epoxy polymer. When HLEBI cut the chemical bonds and generated active terminated atoms with dangling bonds of Epoxy and PTFE polymers in cross-linking zone with chemical bonding around adhesive interface, strengthening the adhesive force indicated by oFp was mainly induced by the chemical bonding, as well as intermolecular attractive force in cross-linking polymers.
  • Investigation of the Microstructure and Corrosion Properties of Friction Stir Processed Cast NiAl Bronze

    pp. 1523-1529

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    DOI:10.2320/matertrans.M2015125

    NiAl bronze (NAB) was produced using the friction stir processing (FSP) technique at various tool rotation rates (ω) and traverse speeds (υ). Optical microstructure (OM) observation results indicated that inhomogeneous microstructures were produced from top to bottom in the stir zone (SZ), cavity defects were found in the retreating side (RS) area due to inadequate fill of NAB material flow during FSP. Results indicate that FSP processing parameters have a significant influence on the microstructure of NAB alloy. An optimized FSP processing map was obtained from the analysis of the pseudo heat index ω2/υ. Five optimum processing parameters were selected from the processing map, which were used to investigate the effect of FSP parameters on the corrosion properties of NAB by the salt fogging corrosion test. It was determined that the corrosion properties were improved by decreasing the rotation rate at a constant traverse speed, and the grain size and the volume fraction of retained β phases were reduced by using the optimum FSP parameters. These results could optimize the microstructure and deepen the understanding of the corrosion behavior of FSP NAB.
  • Effects of Reheating Temperature and Time on the Microstructure and Mechanical Properties of Thixoforged ZW21 Alloy

    pp. 1530-1538

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    DOI:10.2320/matertrans.M2015151

    The effects of reheating temperature and time on the microstructure and mechanical properties of thixoforged ZW21 alloy were investigated. The results indicate that the ZW21 alloy is suitable for thixoforming in view of its thixoformability and the resulting mechanical properties. The reheating temperature and duration mainly affect the microstructure, including the size and fraction of primary particles, the microstructure compactness, the solubilities of the solute elements and W phase content, and thus the mechanical properties of the thixoforged alloy. The effects of the reheating temperature are larger than that of the reheating time. These two parameters have an optimum critical value, and values less than or higher than this value decrease the mechanical properties. The appropriate reheating technique is heating for 70 min at 913 K, and the resulting ultimate tensile strength, elongation, and hardness can be up to 238 MPa, 19.4%, and 58 HV, respectively. As the reheating temperature or reheating time increases, the fracture regime has a tendency to change from intergranular mode to transgranular mode and finally to intergranular mode again.
  • Microstructural Evaluation of Ti(C0.7N0.3)-Mo2C-xNbC-Ni Cermets

    pp. 1539-1543

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    DOI:10.2320/matertrans.Y-M2015817

    The microstructures of Ti(C0.7N0.3)-19Mo2C-xNbC-24Ni cermets (x = 0, 5, 10, 15, and 20) were studied. The cermets consisted of Ti(C,N) and solid-soluted Ti(C,N) as the hard phase with metallic Ni as a binder phase. The solid-soluted Ti(C,N) was found to surround Ti(C,N) phases, forming core-rim structures in the cermets with low NbC content. Phase separation between the Ti(C,N) and solid-soluted Ti(C,N) occurred in the cermets with higher NbC content. TEM analysis showed solid-soluted Ti(C,N) to nucleate surrouunding Ti(C,N) for 5NbC, but in 20NbC it nucleated within the Ni binder phase. The Nb content in the solid-soluted Ti(C,N) of the composite with 20NbC was higher than that of 5NbC. A hard phase separation occurred when the lattice constant of solid-soluted Ti(C,N) exceeded 4.328 Å.
  • Microstructure and Mechanical Properties of Large-Scale Ingots of the Zr-1Mo Alloy

    pp. 1544-1548

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    DOI:10.2320/matertrans.M2015098

    A large-scale ingot of Zr-1Mo alloy was produced for industrial manufacturing to investigate whether it is possible to produce an ingot with homogeneity. The homogeneous ingot with a chemical composition of Zr-1 mass%Mo was prepared successfully. The microstructure, mechanical properties, and magnetic susceptibility were evaluated. The microstructure showed a coarse colony structure of a plate-like α phase and a thin β phase. An ω phase precipitation was observed in the β phase. Elongation of 23% and magnetic susceptibility of 12.4 × 10−9 m3 kg−1 (0.98 × 10−6 cm3 g−1) were achieved. We found that it is possible to produce a homogeneous large-scale ingot of Zr-1Mo with high elongation and low magnetic susceptibility.
  • Radiation Defects Formed in Ion-Irradiated 316L Stainless Steel Model Alloys with Different Si Additions

    pp. 1549-1552

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    DOI:10.2320/matertrans.MAW201503

    The 304/316 series of austenite stainless steels are used in light water reactors as structural materials. As a result of the high temperatures and neutron irradiation in reactor, dislocation defects will form in stainless steel, causing an increase in the hardness and a decrease in the ductility of the material. In this work, high purity 316L stainless steel model alloys with three different Si contents were ion irradiated at 290°C or 400°C to investigate the black dot and Frank loop formation mechanism influenced by Si addition. Black dot defect formation mainly occurs at 290°C. It is Frank loop in nature with its formation not affected by Si addition. Frank loop is the main defect at 400°C, and both loop density and the average size are substantially suppressed by Si addition. This may be caused by silicon’s role in enhancing effective vacancy diffusivity and thus promoting recombination. The trend of irradiation hardening measured verses temperature matches the microstructure observed.
  • Influence of Nb Addition on Phase Constitution and Mechanical Properties of Biomedical Ti-Zr Based Alloys

    pp. 1553-1557

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    DOI:10.2320/matertrans.M2015118

    The influence of Nb addition on phase constitution, microstructure and mechanical properties of biomedical equi-atomic Ti-Zr based alloys was investigated. Phase constitution of Ti-Zr based alloys containing Nb rapidly cooled from β single phase changed with Nb addition as follows: α′ → α′′ + α′ + β → β + α′′ → β. Young’s moduli of Ti-Zr based alloys subjected to water quenching initially decreased with increasing Nb content. The minimal value was obtained in the Ti-48Zr-4Nb (mol%) composition alloy. The Young’s moduli increased in relation to the phase constitution change. In the alloys containing over 4% Nb, their principal phase was changed by subsequent cold rolling, this is mainly because β → α′ and β → α′′ stress-induced martensitic transformation occurred. This phase transformation resulted in a decrease of Young’s modulus. Furthermore, cold rolling impartd anisotropy to the Young’s modulus which caused the value to drop. The Ti-47Zr-6Nb alloy had the lowest value of Young’s modulus after cold rolling in this study, 59.5 GPa.
  • Relation between n-Value and Critical Current in Filamentary and Coated Superconducting Tapes with Tensile Stress-Induced Cracks

    pp. 1558-1564

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    DOI:10.2320/matertrans.MAW201501

    We have determined experimentally that the n-value of tension-damaged bismuth strontium calcium copper oxide (BSCCO, Bi2223) filamentary superconducting tape decreases very sharply with decreasing critical current, compared with bending-damaged tape. In this work, the sharp decrease in the n-value associated with decreasing critical current under applied tensile stress/strain was studied with a current shunting model that assumes cracks in filamentary and coated superconductors. In a filamentary conductor containing collective filament cracks, defined as cracks composed of successively cracked filaments in a transverse cross-section, the decrease in the cross-sectional area of the superconducting current transportable-filaments reduces the critical current, and the shunting current at the crack reduces the n-value. In addition, the decrease in the electrical resistance in the current shunting circuit increases the critical current slightly and decreases the n-value sharply. The experimentally measured relationship between the n-value and the critical current for two BSCCO samples from different manufacturers was described by the upper and lower bounds calculated with the current shunting circuit resistance as a variable. The experimentally measured relationship between the n-value and the critical current for two different coated conductors were described in a similar manner.
  • Sand Cementation Test using Plant-Derived Urease and Calcium Phosphate Compound

    pp. 1565-1572

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    DOI:10.2320/matertrans.M-M2015818

    The investigation of urease containing plant species and the calcium phosphate compounds (CPCs) precipitation along with plant derived urease were performed at laboratory scale. At first, small scale laboratory samples (height, h = 10 cm & inner diameter, ϕ = 5 cm) were made using Toyoura sand and only from CPC solution having different Ca/P ratios to use as control samples. Afterward, another Toyoura sand test pieces were made by mixing watermelon seed extract, urea with different concentrations and CPC solution having different Ca/P ratios to study the optimal cementation. Test pieces were cured up to 28 days in an airtight container at high humidity at 25°C and carried out unconfined compressive strength (UCS) test. The UCS of the sand test pieces cemented by CPC with urease containing plant extract and urea were larger than that of the test pieces without plant extract. Furthermore, the best CPC solution mixture for highest cementation was with the concentration of Ca/P ratio of 0.5. In addition, pH content was measured after UCS test. Maintaining pH around 8 in the specimen at 28 days was significant to get optimal cementation.
  • Substance Flow Analysis of Indium in Taiwan

    pp. 1573-1578

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    DOI:10.2320/matertrans.M2015165

    As indium is an economically important and a limited resource, a better understanding of domestic indium flow in each country is needed. In this study, fate and management of indium in Taiwan, particularly in the manufacturing of light-emitting diode (LED) and thin film transistor-LCD for the year 2011, was carried out using a substance flow analysis (SFA). It was found out that the total consumption of indium by these two products in 2011 was around 271 t-In; out of which, 266 t-In was imported. However, only 10% of this indium was found in the products, and therefore 90% was a potential indium waste. Among these wastes, 53% was treated and recovered outside Taiwan and 47% was domestically recovered. This indicates that the management and recovery technology of indium is of paramount importance in view of the security of indium supply and Taiwan environmental sustainable development.
  • Fundamental Studies on a Recycling System for Precious and Rare Metals Using a Propylene Carbonate Solvent Containing CuBr2 and KBr

    pp. 1579-1584

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    DOI:10.2320/matertrans.M2015202

    Previously we studied a novel process for recycling gold from secondary sources: the leaching of gold using dimethyl sulfoxide solutions containing copper bromide and precipitation with water, which could offer a number of advantages, including eco-friendliness, ease of operation and low cost. In this study, we have further investigated a more environmentally benign solvent, Propylene Carbonate (PC), with CuBr2 and KBr for the leaching and recovery of precious and rare metals. The mechanism of dissolution was investigated using electrochemical measurements. Metal wires were dissolved in a PC solution with 0.2 M of CuBr2 and 0.2 M of KBr at 343 K. Next, 10 ml of dilute sulfuric acid aqueous solution at pH 1 was added to the solution at ambient temperature and shaken to biphasically separate the dissolved metals. The contents of each element in the sulfuric acid and PC phases were measured by ICP-OES. The results of the electrochemical measurements indicated that the anodic dissolution of sample metals in the PC containing CuBr2 occurred at relatively negative potentials and was paired with the cathodic reduction of Cu2+ to Cu+. It was found that Au, Pd, Cu, Sn, Co, Ni and Zn could be dissolved at relatively fast rate, while Ag, Ta, Ti and W could not be dissolved. In addition, 98% of Au and 94% of Pd remained in the PC phase, while most other dissolved metals migrated to the sulfuric acid phase. This indicated that the dissolved Au and Pd could be effectively separated from other metals via biphasic separation with sulfuric acid. Next, the gold in the PC phase was recovered by the reduction of ascorbic acid or calcination. The cost analysis for recovering gold by this system resulted in 0.34 USD/g-Au.
  • Microstructures and Mechanical Properties of 440C Stainless Steel Strengthened with TaC via Vacuum Sintering and Heat Treatments

    pp. 1585-1590

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    DOI:10.2320/matertrans.M2015147

    In this study, different amounts of tantalum carbide (TaC) powders (10, 20 and 30 mass%) were mixed and added to 440C steel powders. The composite powders were sintered at 1270, 1280 and 1290°C, respectively, for 1 h. The experimental results showed that a suitable amount of TaC particle addition was effective in improving the strength and hardness of the composite materials. Conversely, excess TaC hindered the liquid diffusion of the Fe elements. As a result, the 440C specimens with 30% TaC addition still had 1.3% porosity. The 440C specimens with 10% TaC addition sintered at 1270°C possessed the highest TRS values (2260.3 MPa), while those with 20% TaC addition sintered at 1290°C had the highest hardness values (HRA 85.2). The microstructural evaluation of the 440C specimens with 10% TaC addition revealed that all the rod-shaped M7C3 carbides transformed to M23C6 carbides and precipitated within the grains as a strengthening phase after heat treatment, which was advantageous to the transverse rupture strength (TRS). Consequently, the TRS value of the 440C specimens with 10% TaC addition was significantly increased (2260.3 → 2458.4 MPa) after heat treatment, thus possessing a high hardness (HRA 83.8).
  • Effects of Heat Treatment and Extrusion on Microstructure and Properties of A390 Alloy Hollow Billet Fabricated via DC Casting

    pp. 1591-1598

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    DOI:10.2320/matertrans.M2015132

    An A390 alloy hollow billet was fabricated via a DC casting process prior to heat treatment and extrusion. The microstructural evolution and properties of the A390 alloy were studied by means of optical microscopy, scanning electron microscopy (SEM), electrical conductivity, tensile and hardness tests. The results show that primary Si particles experienced a slight change in that the sharp edges and corners became smooth. The eutectic Si particles were partially modified, the morphology changed from needle-like to rod-like and granular and the particle size increased during homogenization and T6 heat treatment. Some coarse primary Si particles fractured with cracks inside or separated into smaller ones, while fine eutectic Si particles being uniformly distributed in the matrix with a more rounded morphology after the extrusion process. Intermetallic phases were still distributed at the grain boundary after homogenization and T6 heat treatment, while the extrusion process was successful in changing the distribution of intermetallic phases to be uniform in the matrix. The Al8FeMg3Si6 (π) phase disappeared and it was substituted by the Al5Cu2Mg8Si6 (Q) and θ phase during homogenization, and Fe was dissolved into the Q phase. The electrical conductivity increased after the heat treatment and extrusion process. The ultimate tensile strength (UTS) and hardness significantly increased after the T6 heat treatment as a result of precipitate hardening. The tensile strength and hardness value were reduced after the extrusion process and that can be ascribed to a small portion of primary Si particles being fractured with crack inside during the extrusion process. However, the elongation increased significantly after the extrusion process and it can be attributed to the microstructural evolution, especially the changes of eutectic Si improved the continuity of the matrix.
  • Electrochemical Corrosion Behavior of AISI 409L Stainless Steel Aluminized by Hot-Dip Coating Method in Automotive Exhaust Gas Solution

    pp. 1599-1604

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    DOI:10.2320/matertrans.M2015134

    This paper focuses on the pitting resistance of hot-dip aluminized (HDA) stainless steel after the depletion of the coating layer formed in the exhaust condensed solution. HDA stainless steel is composed of a coating layer, an interdiffusion layer, and a substrate. In the interdiffusion layer which is mainly composed of Al7(Fe,Cr)2Si and (Fe,Cr)(Al,Si)3, microcracks were observed in the (Fe,Cr)(Al,Si)3 layer. From electrochemical tests, the corrosion potential of the Al-10Si coating-removed 409L is higher than that of the interdiffusion layer-removed 409L. The pit depth of the substrate (anode) exposed by microcracks of the interdiffusion layer (cathode) is drastically increased when the coating layer is extinct.
  • Improvement of Riser Efficiency Using High-Intensity Ultrasonic Treatment in A356 Alloy

    pp. 1605-1608

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    DOI:10.2320/matertrans.M2015141

    We have investigated the effect of ultrasonic vibration on the alloy riser thus reducing the volume and improving the microstructure of molten A356 alloy. A unique horn shape and shrinkage cavity mold was designed for this study. High power ultrasonic vibration was then introduced into the riser of the molten aluminum during solidification of the A356 alloy. As a result, the shrinkage cavities are decreased and the riser efficiency is improved. In addition, the morphology of primary α-Al phase in the casting alloy changes from dendrite to granule in nature after the ultrasonic vibration treatment. This study suggests that ultrasonic vibration can be used to reduce the riser volume in an A356 alloy casting sample.
  • Effect of Zn Content and Solution Treatment on Damping Capacities of Mg–Zn Casting Alloys

    pp. 1609-1612

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    DOI:10.2320/matertrans.M2015203

    The effects of Zn content and solution treatment on the damping capacities of Mg–(0–6)%Zn casting alloys were investigated. In the as-cast state, increasing Zn content led to an increase in the volume fraction of the MgZn phase, and to the deterioration of the damping levels, both in the strain-amplitude-independent and strain-amplitude-dependent regions. The microstructural evaluation indicated that the increased Zn concentration in the α-(Mg) matrix and increased number of MgZn particles are responsible for the deterioration of the damping in the strain-amplitude-independent and strain-amplitude-dependent regions, respectively. The solution-treated Mg–6%Zn alloy exhibited better strain-amplitude-dependent damping than the as-cast one, but the tendency was reversed in the strain-amplitude-independent region. The dissolution of the MgZn phase and the correspondingly increased Zn concentration in the α-(Mg) matrix after the solution treatment can explain the reversed damping behaviors in the strain-amplitude-dependent and strain-amplitude-independent regions, respectively.
  • Editor’s Announcement

    pp. 1613-1613

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    DOI:10.2320/matertrans.EAM2015701

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