Raman Scattering Study of Lattice Dynamics and Phase Transitions in Layered Perovskite Sr2Ta2O7 Ceramics under High Pressure

Strontium tantalate (Sr₂Ta₂O₇) is a ceramic with an orthogonal Cmcm space group phase. Due to its potential applications in the field of multiferroic materials, it has become a research hotspot in recent years. However, the regulatory mechanism and phase transition behavior of hydrostatic pressure on its complex lattice structure remain unclear, which, to some extent, limits the in-depth understanding of the "structure-property" relationship of this material. This study systematically investigates the lattice dynamic response characteristics of orthogonal Cmcm Sr₂Ta₂O₇ under high pressure up to 30 GPa using in-situ high-pressure Raman spectroscopy, marking the highest pressure study conducted on this system to date. The results indicate that when the pressure reaches 5 GPa, significant changes occur in the Raman vibrational modes of the material, a phenomenon attributed to a structural phase transition induced by symmetry breaking, corresponding to a transition from a commensurate phase to an incommensurate phase, consistent with previous research findings on Sr₂Ta₂O₇. As the pressure further increases to 20 GPa, a second phase transition may occur, which is identified as a first-order phase transition closely related to lattice disordering. However, the specific crystal structure of this high-pressure phase remains to be further confirmed in future studies. The Raman spectroscopy analysis suggests that the structural distortion of this high-pressure phase may follow a transformation pathway from orthogonal to monoclinic.