Structural and Mössbauer Studies of Sr1.5Ca1.5Fe2.25Mo0.75O9−δ and Sr1.92Ca1.08Fe2.04W9−δ Double Perovskites

Sr1.50Ca1.50Fe2.25Mo0.75O9−δ and Sr1.92Ca1.08Fe1.04W0.96O9−δ double perovskites are synthesized in the polycrystalline form by a solid-state reaction route in air and studied at room temperature using the of PXRD, Raman and Mossbauer spectroscopy techniques. The Rietveld refinement analysis reveals that both compounds adopt a tetragonal system with the space group I4/m and lattice parameters a = b = 5.5176(1) A and c = 7.8065(2) A for Sr1.50Ca1.50Fe2.25Mo0.75O9−δ and a = b = 5.5453(1) A and c = 7.8388(1) A for Sr1.92Ca1.08Fe2.04W0.96O9−δ. Raman spectra are consistent with the group theoretical analysis predicted for tetragonal symmetry I4/m (point group C 4 5 ). 57Fe Mossbauer spectra recorded at room temperature show a paramagnetic behavior for Sr1.50Ca1.50Fe2.25Mo0.75O9−δ, and magnetic ordering for Sr1.92Ca1.08Fe2.04W0.96O9−δ. The isomer shift (δ) and quadrupole splitting (Δ) values are characteristic of high-spin Fe3+ in a distorted octahedral coordination.