First-principles calculations to investigate pressure-driven phase transition and elastic properties of TlGaSe2

Abstract The optimized crystal structure, Raman spectra, and elastic properties of layered TlGaSe₂ crystal are determined using the first-principles method at pressures between 0 and 12 GPa. The results of the calculations indicate that the lattice constants change sharply at around 0.9 GPa and the c-axis is more compressible than the a- and b-axes. We observe the most striking changes in interatomic Tl–Ga distances. Our investigation results show that TlGaSe₂ undergoes a pressure-induced isostructural phase transition. We have calculated how elastic constants and different elastic properties, like bulk modulus, shear modulus, Young’s modulus, Poisson’s ratio, and Raman active modes, change with pressure. By clarifying the pressure-dependent behavior of TlGaSe₂, this work contributes to the broader understanding of layered semiconductors under compression. Beyond clarifying the pressure-induced phase transition mechanism, our results provide theoretical support for the use of TlGaSe₂ under high pressure in radiation detection, photoacoustic devices, and broadband photodetectors, as suggested in earlier experimental studies.