Pressure-induced 1T to 3R structural phase transition in metallic VSe2: X-ray diffraction and first-principles theory

Abstract

We study pressure-induced structural evolution of vanadium diselenide (VSe2), a 1T polymorphic member of the transition metal dichalcogenide (TMD) family, using synchrotron-based powder x-ray diffraction (XRD) and first-principles density functional theory (DFT). Our XRD results reveal anomalies at P∼4GPa in the c/a ratio, V-Se bond length, and Se-V-Se bond angle, signaling an isostructural transition. This transition is followed by a first-order structural transition from the 1T (space group P¯3m1) phase to a 3R (space group R¯3m) phase at P∼11GPa due to sliding of adjacent Se-V-Se layers. Both the transitions at ∼4 and 11 GPa are cognate with associated changes in the Debye-Waller factors not reported so far. We present various scenarios to understand the experimental results within DFT and find that the 1T to 3R transition is captured using spin-polarized calculations with Hubbard correction (Ueff=U−J=8eV), giving a transition pressure of ∼9 GPa, close to the experimental value.