Quantitative elaboration of the defect structure of iron doped nickel oxide (Ni0.955Fe0.045)1−δO by in situX-ray absorption spectroscopy

Abstract

We have performed in situ X-ray absorption spectroscopy (XAS) on single crystalline iron doped nickel oxide, (Ni_0.955Fe_0.045)_1−δO, at the Fe K-edge at high temperatures (T1273 K) and under defined low oxygen activities. The defect structure of the doped oxide was analyzed by a deconvolution of the extended X-ray absorption fine structure (EXAFS) into the contributions of two different absorber species: (1) substitutional iron ions, located on octahedral sites, and (2) interstitial iron ions, located on tetrahedral sites, and coordinated tetrahedrally by four oxygen ions and four cation vacancies ((4:1)-defect cluster). Cluster fractions and cluster iron–oxygen distances were determined quantitatively as a function of temperature and oxygen activity. Furthermore, it was possible to determine lattice constants and the thermal lattice expansion coefficient under in situ conditions.