Structural studies of SrFeO/sub 3/ and SrFe/sub 0.5/Nb/sub 0.5/O/sub 3/

Complex iron based perovskite type materials having general A(Fe/sub 0.5/B/sub 0.5/)O/sub 3/ where A = Ca, Ba, Sr; B = Nb, Ta, Sb, have attracted considerable attention due to the high dielectric permittivity over wide temperature ranges. The complex perovskites have many important applications in various fields such as gas sensors, catalysts, electrical conductors, magnetoresistance, solid oxide fuel cells (SOFCs), memory devices, multilayer capacitors and ferroelectric relaxers. In these materials, the crystal structure and concentrations of oxygen defects are critical parameters which have pronounced effects on electrical, transport and mechanical properties of these materials. The structural properties of SrFeO/sub 3/ and SrFe/sub 0.5/Nb/sub 0.5/O/sub 3/ were investigated using a combination of X-ray diffraction and X-ray absorption fine structure spectroscopic techniques. Rietveld refinement of the X-ray diffraction data revealed that SrFeO/sub 3/ has a simple cubic perovskite structure, space group Pm-3m; whereas SrFe/sub 0.5/Nb/sub 0.5/O/sub 3/ shows a tetragonal structure within P4mm space group. X-ray absorption results demonstrate that the valence state of Fe in SrFeO/sub 3/, however, it changes to when 50% Nb/sub 5+/ is substituted at the Fe sites. (Orig./A.B.)