Raman Fingerprint of Pressure-Induced Phase Transitions in TiS₃Nanoribbons: Implications for Thermal Measurements under Extreme Stress Conditions

Two-dimensional layered trichalcogenide materials have recently attracted the attention of the scientific community because of their robust mechanical and thermal properties and applications in opto- and nanoelectronics devices. We report the pressure dependence of out-of-plane Ag Raman modes in high quality few-layer titanium trisulfide (TiS3) nanoribbons grown using a direct solid-gas reaction method and infer their cross-plane thermal expansion coefficient. Both mechanical stability and thermal properties of the TiS3 nanoribbons are elucidated by using phonon-spectrum analyses. Raman spectroscopic studies at high pressure (up to 34 GPa) using a diamond anvil cell identify four prominent Ag Raman bands; a band at 557 cm-1 softens under compression, and others at 175, 300, and 370 cm-1 show normal hardening. Anomalies in phonon mode frequencies and excessive broadening in line width of the soft phonon about 13 GPa are attributed to the possible onset of a reversible structural transition. A complete structural phase transition at 43 GPa is inferred from the Ag soft mode frequency (557 cm-1) versus pressure extrapolation curve, consistent with recently reported theoretical predictions. Using the experimental mode Grüneisen parameters γi of Raman modes, we estimated the cross-plane thermal expansion coefficient Cv of the TiS3 nanoribbons at ambient phase to be 1.321 × 10-6 K-1. The observed results are expected to be useful in calibration and performance of next-generation nanoelectronics and optical devices under extreme stress conditions.