We report the structural, vibrational and electrical transport properties up to ~ 16 GPa of the 1T-TiTe2, a prominent layered 2D system, which is predicted to show a series of topologically trivial -nontrivial transitions under hydrostatic compression. We clearly show signatures of two iso-structural transition at ~ 2 GPa and ~ 4 GPa obtained from the minima in c/a ratio concomitant with the phonon linewidth anomalies of Eg and A1g modes at around the same pressures, providing strong indication of unusual electron-phonon coupling associated to these transitions. Resistivity presents nonlinear behavior over similar pressure ranges providing a strong indication of the electronic origin of these pressure driven isostructural transitions. Our data thus provide clear evidences of topological changes at A and L point of the Brillouin zone predicted to be present in the compressed 1T-TiTe2. Between 4 GPa and ~ 8 GPa, the c/a ratio shows a plateau suggesting a transformation from an anisotropic 2D layer to a quasi 3D crystal network. First principles calculations suggest that the 2D to quasi 3D evolution without any structural phase transitions is mainly due to the increased interlayer Te-Te interactions (bridging) via the charge density overlap. In addition to the pressure dependent isostructural phase transitions, our data also evidences the occurrence of a first order structural phase transition from the trigonal (P3 ̅ m1) phase at higher pressures. We estimate the start of this structural phase transition to be ~ 8 GPa and the symmetric of the new high-pressure phase to be monoclinic (C2/m).2
Pressure induced electronic topological transitions in the wide band gap semiconductor Sb 2 S 3 (E g = 1.7-1.8 eV) with similar crystal symmetry (SG: Pnma) to its illustrious analog, Sb 2 Se 3 , has been studied using Raman spectroscopy, resistivity and the available literature on the xray diffraction studies. In this report, the vibrational and the transport properties of Sb 2 S 3 have been studied up to 22 GPa and 11 GPa, respectively. We observed the softening of phonon modes A g (2), A g (3) and B 2g and a sharp anomaly in their line widths at 4 GPa. The resistivity studies also shows an anomaly around this pressure. The changes in resistivity as well as Raman line widths can be ascribed to the changes in the topology of the Fermi surface which induces the electron-phonon and the strong phonon-phonon coupling, indicating a clear evidence of the electronic topological transition (ETT) in Sb 2 S 3 . The pressure dependence of a/c ratio plot obtained from the literature showed a minimum at ~ 5 GPa, which is consistent with our high pressure Raman and resistivity results. Finally, we give the plausible reasons for the non-existence of a non-trivial topological state in Sb 2 S 3 at high pressures.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.