Pressure-induced phase transitions in TmVO4 investigated by Raman spectroscopy

Abstract

The structural behavior of TmVO4 at pressures up to ∼ 55 GPa was investigated by Raman spectroscopy. The changes in Raman spectra suggest the existence of three phase transitions upon compression. The first phase transition appeared at ∼ 7.7 GPa, which was an irreversible phase transition from the ambient-pressure zircon phase to the scheelite phase, confirming previous X-ray measurements. Subsequently, the second reversible phase transition from the scheelite phase to the fergusonite phase occurred at ∼ 23 GPa. Additional changes in the Raman spectra were observed at ∼ 37 GPa, validating the third phase transition. Based on a comparison to related rare earth orthovanadates, we assumed that the post-fergusonite of TmVO4 has an orthorhombic structure described by space group Cmca. The wavenumbers of the Raman modes and their pressure coefficients for all four phases of TmVO4 are reported. Our study provides the vibrational difference in various polymorphs of TmVO4, which will refine our understanding of the structural behavior of rare-earth orthovanadates.