Temperature induced structural phase transition in Sr3-xCaxFe2TeO9 (0 ≤ x ≤ 1) probed by Raman and Mossbauer techniques

A series of perovskites Sr 3ex Ca x Fe 2 TeO 9 (0 x 1) have been prepared in polycrystalline form by solid estate reaction method in air. These materials have been studied by Xeray powder diffraction method (XRPD) and Raman spectroscopy. An analysis of the XRD patterns at room temperature has shown that these compounds crystallize in a tetragonal system, space group I4/m. The structure contains alternating (Fe/Te) 2a O 6 and (Fe/Te) 2b O 6 octahedra, tilted in antiephase in the basal abeplane. The study of Raman spectroscopy at various temperatures shows a transition from tetragonal to cubic phase: I4/m / Fm3 m. This phase transition occurs at highetemperature. Analysis of Raman spectra recorded at several temperatures shows that this phase transition appears near ~375 C for (x ¼ 0), ~435 C for (x ¼ 0.5) and ~451 C for (x ¼ 1). A proportional and gradual increase of temperature phase transition is observed as function of the calcium amount.