Raman and first-principles study of the pressure-induced Mott-insulator to metal transition in bulk FePS3

Abstract

Members of a recently discovered class of two-dimensional materials based on transition metal phosphorous trichalcogenides exhibit an antiferromagnetic ground state and they have potential applications in spintronics. In particular, FePS3 is a Mott insulator with a band gap of ∼ 1.5 eV. In this study, we used Raman spectroscopy and first-principles density functional theoretical analysis to examine the stability of the structure and electronic properties of FePS3 under pressure. Raman spectroscopy detected two phase transitions at 4.6 GPa and 12 GPa, which were characterized by changes in the pressure coefficients of the mode frequencies and the number of symmetry allowed modes. FePS3 transformed from the ambient monoclinic C2/m phase with a band gap of 1.54 eV to another monoclinic C2/m (band gap of 0.1 eV) phase at 4.6 GPa, which was followed by another transition to the metallic trigonal P-31m phase at 12 GPa. Our findings complement those obtained recently in high pressure X-ray diffraction studies. The calculated elastic properties indicated increases in the bulk, shear, and Young's moduli, as well as a significant reduction in the universal elastic anisotropy index as the crystal changed from the ambient monoclinic C2/m phase to the high pressure trigonal P-31m phase.