Investigation of Nanostructured CaO-ZnO Solid Solutions by X-ray Diffraction

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 CaO-ZnO 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.