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

A series of perovskites Sr3-xCaxFe2TeO9 (0 ≤ x ≤  1) have been prepared in polycrystalline form by solid-state reaction method in air. These materials have been studied by X-ray 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)2aO6 and (Fe/Te)2bO6 octahedra, tilted in anti-phase in the basal ab-plane. 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 high-temperature. Analysis of Raman spectra recorded at several temperatures shows that this phase transition appears near ∼375 °C for (x = 0), ∼435 °C for (x = 0.5) and ∼451 °C for (x = 1). A proportional and gradual increase of temperature phase transition is observed as function of the calcium amount.