Sequence of phase transitions induced by chemical composition and high temperature in [Ba2CaWO6](1−x)[Sr2CaWO6]x double perovskite tungsten oxides.

[Ba 2 CaWO 6 ] 1− x [Sr 2 CaWO 6 ] x (0≤ x ≤1) materials were synthesized by the high temperature solid state reaction and firing methods, and characterized using techniques of X-ray diffraction and Raman spectroscopy. The crystal structures were determined by Rietveld refinements on the laboratory X-ray powder diffraction data. As a function of composition, upon increasing the strontium content, the samples exhibit a sequence of three phase transitions: from cubic ( Fm 3 ̅ m ) to tetragonal ( I 4/ m ) to monoclinic structural phases ( I2/m , P2 1 /n ). These transitions have been confirmed by Raman studies Fm 3 ¯ m x = 0 → I 4 / m 0.1 ≤ x ≤ 0.2 → I 2 / m 0.3 ≤ x ≤ 0.5 → P 2 1 / n 0.6 ≤ x ≤ 1 Furthermore, increasing the temperature for the compositions [Ba 2 CaWO 6 ] 1− x [Sr 2 CaWO 6 ] x (0.1≤ x <1), manifests the P 2 1 / n to I 2/ m , the I 2/ m to I 4/ m and the I 4/ m to Fm 3 ̅ m phase transitions. For the compositions (0.1≤ x ≤0.2) the tetragonal to cubic phase transition is well illustrated. For the room temperature I 2/ m monoclinic compositions, two phase transitions were observed for all the compositions with x ranging from 0.3 to 0.5: from the monoclinic ( I 2/ m ) to tetragonal ( I 4/ m ), and from I 4/ m to Fm 3 ̅ m structures. Finally, for the room temperature P 2 1 /n monoclinic compositions, only two phase transitions are observed in the temperature range probed by Raman spectroscopy, the temperature was not high enough to reach the tetragonal-to-cubic phase transition. [ABSTRACT FROM AUTHOR]