Growth, characterization, and Raman spectra of the 1T phases of TiTe₂, TiSe₂, and TiS₂

Abstract

High-quality large 1T phase of TiX 2 (X = Te, Se, and S) single crystals have been grown by chemical vapor transport using iodine as a transport agent. The samples are characterized by compositional and structural analyses, and their properties are investigated by Raman spectroscopy. Several phonon modes have been observed, including the widely reported A 1g and Eg modes, the rarely reported Eu mode (∼183 cm−1 for TiTe2, and ∼185 cm−1 for TiS2), and even the unexpected K mode (∼85 cm−1) of TiTe2. Most phonons harden with the decrease of temperature, except that the K mode of TiTe2 and the Eu and “A 2u /Sh” modes of TiS2 soften with the decrease of temperature. In addition, we also found phonon changes in TiSe2 that may be related to charge density wave phase transition. Our results on TiX 2 phonons will help to understand their charge density wave and superconductivity.

Pressure-modulated lattice structural evolution in TiS2

“…The E g mode is associated with the in-plane anti-phase movement of S atoms, while the A 1g mode is related to the out-of-plane oscillation of the S atoms in an anti-phase manner. 42 As shown in Fig. 2, two sharp Raman peaks E g (∼234.4 cm −1 ) and A 1g (∼332.5 cm −1 ) modes are obtained in TiS 2 , which are well consistent with the previous experiments.…”

“…According to the group-theoretical analysis, six vibrational modes are associated with TiS 2 with the following irreducible representation 42,43 Γ = 2A 2u + 2E u + A 1g + E g ,where E g and A 1g are Raman active; while E u and A 2u are infrared active. The E g mode is associated with the in-plane anti-phase movement of S atoms, while the A 1g mode is related to the out-of-plane oscillation of the S atoms in an anti-phase manner.…”

“…2, two sharp Raman peaks E g (∼234.4 cm −1 ) and A 1g (∼332.5 cm −1 ) modes are obtained in TiS 2 , which are well consistent with the previous experiments. 37,38,42,43 Additionally, two shoulder peaks were observed at the left side of the E g mode and the right side of the A 1g mode, which are labeled as Sh(E g ) and Sh(A 1g ), respectively. According to the previous report, both the Sh(E g ) and Sh(A 1g ) are associated with the spontaneous excess of interlayer Ti atoms in TiS 2 .…”

Single-crystal growth of layered metallic materials of TiTe2 based on a polytelluride flux method

“…2b displays the Raman spectrum of TiTe 2 , where three prominent resonance peaks could be observed at 140, 123, and 97 cm −1 , corresponding to the out-of-plane A 1g , zone-folded Raman-active M, and in-plane E g vibration modes, indicating the 1T-type structure of the TiTe 2 obtained in this work. 43…”

Investigation of the Electron–Phonon Coupling in Dirac Semimetal PdTe2 via Temperature‐Dependent Raman Spectroscopy

“…Accompanying graphene, layered transition metal dichalcogenides (TMDs) are extensively investigated in academic and industrial communications. [ 1–3 ] Among them, the emerging noble TMDs (NTMDs) with noble metals (Pt and Pd) and chalcogenides (S, Se, and Te) with almost filled d orbitals and a strongly hybridized p z orbital of interlayer chalcogen atoms have gained considerable attention in the past few years. [ 4,5 ] As one of NTMDs, metallic layered palladium ditelluride (PdTe 2 ) exhibits high electrical (≈4.3 × 10 6 S m −1 ) and thermal (≈130 W m −1 K −1 ) conductivity, high charge carrier mobility (2735 ± 112 and 2570 ± 234 cm 2 V −1 s −1 in c ‐ and ab ‐axes), excellent ambient and thermal stability, anisotropic in‐plane properties, and distinct topological superconductivity ( T c = ≈1.7 K) due to the increased electron–phonon (e–ph) coupling.…”