Evolution of Raman and Mössbauer spectra at high pressures up to 75 GPa and a phase transition in CaSnO3 perovskite

Abstract

Raman and Mossbauer spectra from 119Sn nuclei in CaSnO3 perovskite have been studied at high pressures up to 75 GPa. A linear increase in the frequency of the main Raman modes and a monotonic decrease in the isomer shift in Mossbauer spectra in the pressure range of 0–40 GPa are established. It is shown that the pressure-induced increase in Raman frequencies can be associated with the variation of the angle between the Sn–O–Sn bonds in chains of oxygen octahedra SnO6 along the c axis. The sharp variation of the parameters of the Raman and Mossbauer spectra is observed in the pressure region of 40–55 GPa, indicating the structural phase transformations, which can be associated with the transition into the post-perovskite state. Raman spectra of CaSnO3 samples with the ilmenite structure have been obtained for the first time.