Synthesis, crystal Structure and temperature induced phase transition in (Ba1/5Sr4/5)2NiMoO6 double perovskite oxide: Study by X-ray diffraction and Raman spectroscopy

BaCO3, SrCO3, NiO, MoO3 precursors were used as starting materials in the synthesis of double perovskite (Ba1/5Sr4/5)2NiMoO6, and their crystal structure at room tempertaure was solved using X-ray powder diffraction. The Rietveld analysis of X–ray powder diffraction patterns show that both compounds adopt a tetragonal structure with space group I4/m, with unit cell parameters a= 5.58537(1) Å, c=7.9066(2) Å. The structure can be represented as a three-dimensional network of alternating NiO6 and MoO6 octahedra, with Ba and Sr atoms occupying the interstitial spaces. Temperature-induced phase transitions of (Ba1/5Sr4/5)2NiMoO6 were investigated by mean of Raman spectroscopy technique at high temperature up to 392 °C. remarkable in the behaviuor of temperature dependence of the modes has been interpreted as a phase transition from the tetragonal (I4/m) to the cubic (3Fmm) structure