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

摘要

Raman and Mossbauer spectra from Sn-119 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.