Cation Distribution in ZnCr2O4 Nanocrystals Investigated by X-ray Absorption Fine Structure Spectroscopy

ZnCr2O4 nanocrystals with different sizes were synthesized by a coprecipitation and postcalcined method. X-ray powder diffraction and transmission electron microscopy showed that the nanocrystals annealed at different temperatures have the same crystal structure and their size increases with increasing annealing temperature. Cr and Zn K-edge X-ray absorption near edge spectroscopy (XANES) and extended X-ray absorption fine structure (EXAFS) was used to investigate the change of the inversion parameter vs the annealing temperature. The inversion parameter is found to decrease with increasing annealing temperature. In particular, the sample annealed at 750 degrees C has a normal spinel structure, like bulk ZnCr2O4. On the contrary, the inversion parameter of the sample annealed at 300 degrees C can get 0.24. This study of ZnCr2O4 shows for the first time a variation of the inversion degree with annealing temperature, and provides a method to obtain ZnCr2O4 with different inversion parameters.