Structural, vibrational, and electrical properties of 1T−TiTe2 under hydrostatic pressure: Experiments and theory

Abstract

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

Room Temperature Commensurate Charge Density Wave in Epitaxial Strained TiTe2 Multilayer Films

“…In our epitaxial films though the situation is different, because a significant interaction with the substrate is established as evidenced from the Moiré pattern (Figure a,b) and the perfect rotational alignment of the epilayer with the substrate (Figure ). The latter interaction produces anisotropic strain such that the in‐plane parameter is enlarged and the out of plane parameter along the c ‐axis is compressed by 2.3% as accurately measured by synchrotron GIXD, yielding an estimated stress ≈0.6–0.8 GPa if a measured bulk modulus B ≈ 0.28–0.40 GPa is assumed. The compression results in an appreciable reduction of van der Waals gap from ≈3.2 Å to the value of 3.1 Å that we measured by STEM bringing the Te–Ti–Te trilayers closer between each other thus enhancing interlayer Te–Te interactions, signifying a transition from a 2D to a 3D‐like TiTe 2 crystal.…”

Novel Superstructure-Phase Two-Dimensional Material 1T-VSe2 at High Pressure

“…According to the XRD results and first-principles calculations, the highpressure superstructure phase is associated with both the distortion of the structure and Fermisurface nesting. The isostructural transitions in TMDs are commonly observed under high pressure 23,24 . However, it is unusual that application of high pressure induces a new symmetrized phase with a super-lattice, when pressure commonly suppresses such superstructures.…”

Real and virtual polymorphism of titanium selenide with robust interatomic potentials

“…47) as shown by the evolution of the characteristic Raman signatures of fundamental optical phonon modes in TiSe 2 . It is proposed that as with 1T-TiTe 2 and IrTe 2 , 48,49 the TiSe 2 undergoes a transition to a non-layered monoclinic C2/m phase structure. We have checked this hypothesis using both our newly developed PSM IP and ab initio calculations in the range of relevant pressures.…”