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

The strontium tantalate Sr₂Ta₂O₇ is a ceramic with an orthogonal Cmcm space group. Due to its potential applications in the field of multiferroics, 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 by using in-situ high-pressure Raman spectroscopy, marking the highest pressure on this system to date. The results manifest that when the pressure reaches 5 GPa, significant changes occur in the Raman vibrational modes of the material. This phenomenon is attributed to a commensurate-to-incommensurate structural transition induced by symmetry breaking, consistent with previous research findings on Sr₂Ta₂O₇. As the pressure further increasing 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.