Synthesis, structure, and high temperature Mössbauer and Raman spectroscopy studies of Ba 1.6Sr 1.4Fe 2WO 9 double perovskite

Abstract

Ba 1.6Sr 1.4Fe 2WO 9 has been prepared in polycrystalline form by solid-state reaction method in air, and has been studied by X-ray powder diffraction method (XRPD), and high temperature Mössbauer and Raman spectroscopies. The crystal structure was resolved at room temperature by the Rietveld refinement method, and revealed that Ba 1.6Sr 1.4Fe 2WO 9 crystallizes in a tetragonal system, space group I4/m, with a = b = 5.6489(10)Å, c = 7.9833(2)Å and adopts a double perovskite-type A 3B′ 2B″O 9 (A = Ba, Sr; B′ = Fe/W, and B″ = Fe/W) structure described by the crystallographic formula (Ba 1.07Sr 0.93) 4d(Fe 0.744W 0.256) 2a(Fe 0.585W 0.415) 2bO 6. The structure contains alternating [(Fe/W) 2aO 6] and [(Fe/W) 2bO 6] octahedra. Mössbauer studies reveal the presence of iron in the 3+ oxidation state. The high temperature Mössbauer measurements showed a magnetic to paramagnetic transition around 405 ± 10 K. The transition is gradual over the temperature interval. The decrease in isomer shift is in line with the general temperature dependence. While the isomer shift is rather linear over the whole temperature range, the quadratic dipolar Δ E temperature dependence shows an abrupt change at 405 K. The latter results allow concluding that a temperature-induced phase transition had occurred. The high temperature Raman study confirms the Mössbauer results on the magnetic to paramagnetic transition.