Temperature-induced phase transition of Ca2AlSiO5.5: Raman spectroscopic study

Abstract

The Raman spectra of low-pressure and high-pressure Ca2AlSiO5.5 oxygen-deficient perovskites have been investigated in the temperature range of 153–1273 K at ambient pressure. No phase transition was observed for low-pressure Ca2AlSiO5.5 in this study, but an irreversible phase transition was observed for high-pressure Ca2AlSiO5.5 at 1223 K. The recovered sample of high-pressure Ca2AlSiO5.5 from 1273 K was confirmed as a single homogeneous phase (high-temperature Ca2AlSiO5.5). The Raman spectra of high-temperature Ca2AlSiO5.5 phase have also been studied in the temperature range of 153–1273 K at ambient pressure. All the observed Raman active bands of the three samples showed linear temperature dependence with different slopes. The quantitative temperature dependences of Raman bands are -2.90 × 10−2 ˜ -0.31 × 10−2, -3.56 × 10−2 ˜ -0.50 × 10−2, and -3.20 × 10−2 ˜ 0.28 × 10−2 cm-1 K-1 for low-pressure, high-pressure and high-temperature Ca2AlSiO5.5, respectively. The isobaric mode Grüneisen parameters of low-pressure Ca2AlSiO5.5 were calculated by using present high-temperature Raman spectra combined with a previous result of the thermal expansion coefficient, varying from 0.08 to 1.10 with an average of 0.35.