Investigation of Nanostructured CaO-ZnO Solid Solutions by X-ray Diffraction
Jesper T. N. KNIJNENBURG
Nanostructured zinc oxide (ZnO) is a versatile material with a wide range of applications ranging from nutrition to light-emitting devices, and doping of ZnO with calcium (Ca) may improve its performance. However, there is only a limited understanding of the crystalline properties of nanostructured CaO-ZnO systems. Here, nanostructured Ca-doped ZnO was produced by flame spray pyrolysis and characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). No Ca-Zn oxide phase with specific stoichiometry was formed, but an increase in the ZnO unit cell parameters was observed with increased Ca content. Using Vegard’s law, approximately 2.8 at% Ca was incorporated substitutionally for Zn in nano-ZnO, in agreement with solubility limits reported for bulk ZnO. These results indicate that there is no specific particle size effect for the formation of CaOZnO solid solutions. This Ca incorporation inside the ZnO wurtzite structure resulted in a transformation from slightly elongated to more spherical crystals, as indicated by the ZnO aspect ratio and TEM images.