The high-pressure phase transition in tin diselenide discovered by Raman scattering and X-ray diffraction analysis

Abstract

The two-dimensional (2D) semiconductor tin diselenide (SnSe₂) has recently gained great attention in electronic and optical attributed to its unique physical properties. Here, we present a pressure-dependent study on the phase transformation behavior of the SnSe₂ crystal range from ambient pressure up to 34.81 GPa. In order to study the phase transition behavior of SnSe₂, we employed In situ, high-pressure Raman spectroscopy and X-ray diffraction (XRD). The obtained single-crystal XRD data reveal that at 34.81 GPa, the lengths of the a and c axes are reduced by approximately 9.2 % and 21.7 %, respectively, compared to their values at 0 GPa. This indicates that the lattice parameter a is less affected by pressure compared to the lattice constant c. At a pressure of up to 8 GPa, the low-frequency vibrational mode (approximately 119 cm⁻¹) becomes significantly weaker and then undetectable. Surprisingly, a Raman band gradually emerges at around 80 cm⁻¹. Additionally, the high-frequency vibrational mode gradually splits into two modes, and the Raman signal weakens and broadens. These phenomena suggest a decrease in the crystalline symmetry of SnSe₂ and the occurrence of semiconductor-to-metal transitions from 8 GPa onward. Our findings offer a new avenue for further investigation into the complex phase transition mechanisms in transition metal dichalcogenides-related materials.