Synthesis, structure, and high temperature Mössbauer and Raman spectroscopy studies of Ba1.6Sr1.4Fe2WO9 double perovskite

Ba1.6Sr1.4Fe2WO9 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 Ba1.6Sr1.4Fe2WO9 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 A3B′2B″O9 (A = Ba, Sr; B′ = Fe/W, and B″ = Fe/W) structure described by the crystallographic formula (Ba1.07Sr0.93)4d(Fe0.744W0.256)2a(Fe0.585W0.415)2bO6. The structure contains alternating [(Fe/W)2aO6] and [(Fe/W)2bO6] 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 ΔE 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.

Research highlights▶ Synthesis and characterization of new double perovskites, apatites, orthophosphates and orthovanadates. ▶ High pressure and high temperature studies of double perovskite, orthophosphates, orthovanadates and MAX phases, using XRD, synchrotron radiations, Raman spectroscopy, magnetism, Mössbauer. ▶ Pressure, temperature and compositions induced phase transitions in these materials. ▶ Structural determination/refinement of these compounds as a function of temperature, pressure and composition.