Chemical ordering and pressure-induced isostructural and electronic transitions in MoSSe crystal (original) (raw)
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Journal of physics. Condensed matter : an Institute of Physics journal, 2017
High pressure Raman spectroscopy of bulk 2H-MoTe2 up to ∼29 GPa is shown to reveal two phase transitions (at ∼6 and 16.5 GPa), which are analyzed using first-principles density functional theoretical calculations. The transition at 6 GPa is marked by changes in the pressure coefficients of A 1g and [Formula: see text] Raman mode frequencies as well as in their relative intensity. Our calculations show that this is an isostructural semiconductor to a semimetal transition. The transition at ∼16.5 GPa is identified with the changes in linewidths of the Raman modes as well as in the pressure coefficients of their frequencies. Our theoretical analysis clearly shows that the structure remains the same up to 30 GPa. However, the topology of the Fermi-surface evolves as a function of pressure, and abrupt appearance of electron and hole pockets at [Formula: see text] GPa marks a Lifshitz transition.
High pressure phase transition in metallic LaB 6: Raman and X-ray diffraction studies
Solid State Communications, 2004
High pressure Raman and angle dispersive X-ray diffraction (ADXRD) measurements on the metallic hexaboride LaB 6 have been carried out upto the pressures of about 20 GPa. The subtle phase transition around 10 GPa indicated in Raman measurements is confirmed by ADXRD experiments to be a structural change from cubic to orthorhombic phase. Ab-initio electronic band structure calculations using full potential linear augmented plane wave method carried out as a function of pressure show that this transition is driven by the interception of Fermi level by electronic band minimum around the transition pressure.
Physical Review B, 2018
We report high-pressure Raman scattering measurements on the tetragonal phase of InTe corroborated with the first-principles density functional theory and synchrotron x-ray diffraction measurements. Anomalous pressuredependent linewidths of the A 1g and E g phonon modes provide evidence of an isostructural electronic transition at ∼3.6 GPa. The first-principles theoretical analysis reveals that it is associated with a semiconductor-to-metal transition due to increased density of states near the Fermi level. Further, this pressure induced metallization acts as a precursor for structural phase transition to a face centered cubic phase (F m3m) at ∼6.0 GPa. Interestingly, theoretical results reveal a pressure induced band inversion at the Z and M points of the Brillouin zone corresponding to pressures ∼1.0 and ∼1.4 GPa, respectively. As the parity of bands undergoing inversions is the same, the topology of the electronic state remains unchanged, and hence InTe retains its trivial band topology (Z 2 = 0). The pressure dependent behavior of the A 1g and E g modes can be understood based on the results from the synchrotron x-ray diffraction, which shows anisotropic compressibility of the lattice in the a and c directions. Our Raman measurements up to ∼19 GPa further confirms the pressure induced structural phase transition from a face-centered to primitive cubic (F m3m to P m3m) at P ∼ 15 GPa.
Vibrational study of HgGa2S4 under high pressure
Journal of Applied Physics, 2013
Stimulated crystallization of melt-quenched Ge2Sb2Te5 films employing femtosecond laser double pulses J. Appl. Phys. 112, 123520 (2012) Controlled joining of Ag nanoparticles with femtosecond laser radiation J. Appl. Phys. 112, 123519 (2012) Structural, elastic, and vibrational properties of layered titanium dichalcogenides: A van der Waals density functional study
Pressure-induced topological phase transitions in rocksalt chalcogenides
Physical Review B, 2013
By means of a comprehensive theoretical investigation, we show that external pressure can induce topological phase transitions in IV-VI semiconducting chalcogenides with rock-salt structure. These materials satisfy mirror symmetries that are needed to sustain topologically protected surface states, at variance with time-reversal symmetry responsible for gapless edge states in Z2 topological insulators. The band inversions at high-symmetry points in the Brillouin zone that are related by mirror symmetry, are brought about by an "asymmetric" hybridization between cation and anion sp orbitals. By working out the microscopic conditions to be fulfilled in order to maximize this hybridization, we identify materials in the rock-salt chalcogenide class that are prone to undergo a topological phase transition induced by pressure and/or alloying. Our model analysis is fully comfirmed by complementary advanced first-principles calculations and ab initio-based tight-binding simulations.
Broadband Infrared Study of Pressure-Tunable Fano Resonance and Metallization Transition in 2H-MoTe2
2021
High pressure is a proven effective tool for modulating inter-layer interactions in semiconducting transition metal dichalcogenides, which leads to significant band structure changes. Here we present an extended infrared study of the pressure-induced semiconductor-to-metal transition in 2H-MoTe2, which reveals that the metallization process at 13÷15 GPa is not associated with the indirect band gap closure, occuring at 24 GPa. A coherent picture is drawn where n-type doping levels just below the conduction band minimum play a crucial role in the early metallization transition. Doping levels are also responsible for the asymmetric Fano line-shape of the E1u infrared-active mode, which has been here detected and analyzed for the first time in a Transition Metal Dichalcogenide compound. The pressure evolution of the phonon profile under pressure shows a symmetrization in the 13÷15 GPa pressure range, which occurs simultaneously with the metallization and confirms the scenario proposed f...
1996
Triclinic rhenium disulphide (ReS 2) is a promising candidate for postsilicon electronics because of its unique optic-electronic properties. The electrical and optical properties of ReS 2 under high pressure, however, remain unclear. Here we present a joint experimental and theoretical study on the structure, electronic, and vibrational properties, and visible-light responses of ReS 2 up to 50 GPa. There is a direct-to-indirect band-gap transition in 1T-ReS 2 under low-pressure regime up to 5 GPa. Upon further compression, 1T-ReS 2 undergoes a structural transition to distorted-1T phase at 7.7 GPa, followed by the isostructural metallization at 38.5 GPa. Both in situ Raman spectrum and electronic structure analysis reveal that interlayer sulfur-sulfur interaction is greatly enhanced during compression, leading to the remarkable modifications on the electronic properties observed in our subsequent experimental measurements, such as band-gap closure and enhanced photoresponsiveness. This study demonstrates the critical role of pressure in tuning materials properties and the potential usage of layered ReS 2 for pressure-responsive optoelectronic applications.
Cornell University - arXiv, 2020
A detailed high pressure study is carried out on 1T ′ MoTe 2 using X-ray diffraction(XRD) and Raman spectroscopy measurements upto about 30.5 GPa. High pressure XRD measurements show no structural transition. All the lattice parameters exhibit anomalous changes in the pressure region 8.4 to 12.7 GPa. Compressibility of the sample is found to be reduced by almost four times above 12.7 GPa with respect to that below 8.4 GPa. The anomalies in the Raman mode corresponding to the out of plane vibrations of Mo atoms sitting in the unit cell surface indicate a strong electron phonon coupling possibly mediated by differential strain inside the unit cell.
Infrared Study of the Pressure-Induced Isostructural Metallic Transition in Mo0.5W0.5S2
Ternary compounds of Transition Metal Dichalcogenides are emerging as an interesting class of crystals with tunable electronic properties, which make them attractive for nano-electronic and optoelectronic applications. Among them, Mo x W 1−x S 2 is one of the most studied alloys, due to the well-known, remarkable features of its binary constituents, MoS 2 and WS 2. The band-gap of this compound can be modelled varying Mo and W percentages in the sample, and its vibrational modes result from a combination of MoS 2 and WS 2 phonons. In this work, we report transmission measurements on a Mo 0.5 W 0.5 S 2 single crystal in the far-infrared range. Absorbance spectra collected at ambient conditions enabled, for the first time, a classification of the infrared-active phonons, complementary to Raman studies. High-pressure measurements allowed to study the evolution of both the lattice dynamics and the free carrier density up to 31 GPa, indicating the occurrence of an isostructural semiconductor-to-metal transition above 18 GPa.