XANES analyses on minor elements and X–ray single crystal structure analyses of Ce– and Nb–perovskite

Abstract

Structural analysis of Ce– and Nb–perovskites containing Fe, Zr, Nb, and rare earth elements (REEs) in CaTiO₃ perovskite was performed using single–crystal X–ray diffraction and X–ray absorption near–edge structure (XANES) analyses. Based on chemical analysis results, XANES measurements and the site–occupation of elements at A– and B–sites showed the chemical formula:
(Ca²⁺_0.817REE³⁺_0.087Na⁺_0.081Sr²⁺_0.005Th⁴⁺_0.003)^1.998+_0.993
(Ti⁴⁺_0.941Nb⁵⁺_0.017Fe³⁺_0.013V⁵⁺_0.010Fe²⁺_0.007Sc³⁺_0.006Zn²⁺_0.005
Al³⁺_0.002Ge⁴⁺_0.001W⁶⁺_0.001)^3.996+_1.003O₃ for Ce–perovskite and
(Ca²⁺_0.937Ce³⁺_0.021Na⁺_0.020La³⁺_0.015Sr²⁺_0.003)^2.008+_0.996
(Ti⁴⁺_0.730Nb⁵⁺_0.122Fe³⁺_0.108Al³⁺_0.020Zr⁴⁺_0.009V⁵⁺_0.008)^3.990+_0.997O₃
for Nb–perovskite. In Ce– and Nb–perovskites, the total charges at the A– and B–sites achieved near–ideal divalent and tetravalent states such as Ca²⁺Ti⁴⁺O₃, respectively, due to complex elemental substitutions. Local distortions around Ti in the perovskite solid solutions were greater, and the pre–edge features of the Ti atoms in Ce– and Nb–perovskites were different from those in pure CaTiO₃. The valence states and local structures of Fe in Ce– and Nb–perovskites were significantly different. The existence of divalent Fe²⁺ at the B–site in Ce–perovskite was confirmed. It is presumed that the displacement ellipsoids of all atoms and local irregularities in Ce–perovskite increase owing to the radiative decay of the actinoid element Th. We reconfirmed that the composition and three–dimensional structure of perovskite–type structures were flexible and caused various electrical, structural changes.