Structural and Transport Properties of 1T-VSe2 Single Crystal Under High Pressures

Abstract

Two-dimensional transition metal dichalcogenide 1T-VSe2 exhibits a unique three-dimensional charge density wave (CDW) order below ∼110 K at ambient pressure, which shows unusual evolution under pressure. Here we report on the high-pressure structural and transport properties of 1T-VSe2 by extending the pressure up to 57.8 GPa, through electrical transport, synchrotron X-ray diffraction (XRD) and Raman scattering measurements, which unravel two critical pressure points. The CDW transition is found to be enhanced under compression at a rate of 16.5 K/GPa up to the first critical pressure PC1 ∼ 12 GPa, at which a structural phase transition from hexagonal P-3m1 to monoclinic C2/m phase takes place. The second critical pressure PC2 ∼ 33 GPa corresponds to another structural transition from monoclinic C2/m to P21/m phase. These findings extend the phase diagram of pressurized 1T-VSe2 and may help to understand pressure tuning of structures in transition metal dichalcogenides.

Pressure-Induced Phase Transition in Multilayered Vanadium Diselenide Nanosheets

“…Similar softening of the A 1g phonon in multilayered MoS 2 is attributed to charge transfer between MoS 2 layers . In contrast, in bulk VSe 2 , the Raman bands are only hardened that is increase in frequency with pressure. New Raman bands at 157, 174, 225, and 233 cm –1 appear around 6.7 GPa (Figure a), probably indicating the onset of the structural transition to the monoclinic phase.…”

“…The newly observed peaks in the diffraction pattern at 7.8 GPa could be satisfactorily fitted in a monoclinic lattice ( C 2/ m ), in accord with an earlier report . The observed transition pressure around 7.8 GPa is found to be nearly half of that observed in bulk VSe 2 single crystal (transition pressure ∼13.2 GPa) . The refined unit cell parameters of high-pressure monoclinic ( C 2/ m ) phase are obtained as: a = 5.671(6) Å, b = 3.249(4) Å, c = 5.657(9) Å, β = 90.33(2)°, and V = 102.689(5) Å 3 with Z = 2 at 7.8 GPa.…”

From Two-, One-, to Zero-Dimensional Vacancies: A Densification Pattern for a Typcial Transition-Metal Dichalcogenide of TiSe2

“…Previous Raman experiment shows the structural stability of the trigonal (1 T ) phase is up to ∼15.0 GPa, and another phase proposed as a monoclinic phase (space group: C 2/ m ) starts to emerge above 15 GPa, which agrees with our calculations. In addition, the 1 T -TiTe 2 , which is isostructural to 1 T -TiSe 2 , has already been confirmed in several independent experiments within the structural transformation from the P -3 m 1 phase to the C 2/ m phase. − This structural transformation also occurs for other TMD materials such as TaS 2 , IrTe 2 , and VSe 2 , but with different transition pressures (20, 5, and 12 GPa for TaS 2 , IrTe 2 , and VSe 2 , respectively). Further increasing the pressure, TiSe 2 will then transform to a hexagonal Fe 2 P-type structure (space group P -62 m , No.…”

“…In addition, the 1T-TiTe 2 , which is isostructural to 1T-TiSe 2 , has already been confirmed in several independent experiments within the structural transformation from the P-3m1 phase to the C2/m phase. 33−35 This structural transformation also occurs for other TMD materials such as TaS 2 , 21 IrTe 2 , 22 and VSe 2 , 23 but with different transition pressures (20, 5, and 12 GPa for TaS 2 , IrTe 2 , and VSe 2 , respectively). Further increasing the pressure, TiSe 2 will then transform to a hexagonal Fe 2 P-type structure (space group P-62m, No.…”

“…18,19 As a basic thermodynamic variable, pressure would change the chemical bonding between the atoms, resulting in the occurrence of new structures with novel physical properties. For example, the ambient trigonal P-3m1 phase of TMDs undergoes a transformation to a monoclinic C2/m phase (TiTe 2 at 12 GPa, 20 TaS 2 at 20 GPa, 21 IrTe 2 at 5 GPa, 22 and VSe 2 at 12 GPa 23 ) and then to exhibit different phases at higher pressure such as the hexagonal Fe 2 P-type structure (TiTe 2 at 33 GPa 20 ) and the tetragonal I4/mmm phase (TaS 2 at 60 GPa, 21 TiS 2 at 52 GPa, 24 and HfSe 2 at 47.2 GPa 25 ). In spite of numerous studies on high-pressure phases of TMDs, a unified model to describe the structural transformations of TMDs is still absent, and thus, those high-pressure phases appear to be occasional and random.…”