Pressure-induced electronic topological transition in Sb2S3

Pressure induced topological and topological crystalline insulators

Research on topological and topological crystalline insulators (TCIs) is one of the most intense and exciting topics due to its fascinating fundamental science and potential technological applications. Pressure (strain) is one potential pathway to induce the non-trivial topological phases in some topologically trivial (normal) insulating or semiconducting materials. In the last ten years, there have been substantial theoretical and experimental efforts from condensed-matter scientists to characterize and understand pressure-induced topological quantum phase transitions (TQPTs). In particular, a promising enhancement of the thermoelectric performance through pressure-induced TQPT has been recently realized; thus evidencing the importance of this subject in society. Since the pressure effect can be mimicked by chemical doping or substitution in many cases, these results have opened a new route to develop more efficient materials for harvesting green energy at ambient conditions. Therefore, a detailed understanding of the mechanism of pressure-induced TQPTs in various classes of materials with spin-orbit interaction is crucial to improve their properties for technological implementations. Hence, this review focuses on the emerging area of pressure-induced TQPTs to provide a comprehensive understanding of this subject from both theoretical and experimental points of view. In particular, it covers the Raman signatures of detecting the topological transitions (under pressure), some of the important pressure-induced topological and TCIs of the various classes of spin-orbit coupling materials, and provide future research directions in this interesting field.

Interlaboratory study on Sb2S3 interplay between structure, dielectric function, and amorphous-to-crystalline phase change for photonics

Antimony sulfide, Sb2S3, is interesting as the phase-change material for applications requiring high transmission from the visible to telecom wavelengths, with its band gap tunable from 2.2 to 1.6 eV, depending on the amorphous and crystalline phase. Here we present results from an interlaboratory study on the interplay between the structural change and resulting optical contrast during the amorphous-to-crystalline transformation triggered both thermally and optically. By statistical analysis of Raman and ellipsometric spectroscopic data, we have identified two regimes of crystallization, namely 250°C ≤ T < 300°C, resulting in Type-I spherulitic crystallization yielding an optical contrast Δn ∼ 0.4, and 300 ≤ T < 350°C, yielding Type-II crystallization bended spherulitic structure with different dielectric function and optical contrast Δn ∼ 0.2 below 1.5 eV. Based on our findings, applications of on-chip reconfigurable nanophotonic phase modulators and of a reconfigurable high-refractive-index core/phase-change shell nanoantenna are designed and proposed.

Anomalous enhancement of atomic vibration induced by electronic transition in 2H-MoTe2under compression

In this work, we explore the atomic vibration and local structure in 2H-MoTe₂by using high-pressure x-ray absorption fine structure spectroscopy up to ∼20 GPa. The discrepancy between the Mo-Te and Mo-Mo bond length in 2H-MoTe₂obtained from extended-XAFS and other techniques shows abnormal increase at 7.3 and 14.8 GPa, which is mainly due to the abrupt enhancement of vibration perpendicular to the bond direction.Ab initiocalculations are performed to study the electronic structure of 2H-MoTe₂up to 20 GPa and confirm a semiconductor to semimetal transition around 8 GPa and a Lifshitz transition around 14 GPa. We attribute the anomalous enhancement of vibration perpendicular to the bond direction to electronic transitions. We find the electronic transition induced enhancement of local vibration for the first time. Our finding offers a novel insight into the local atomic vibration and provides a new platform for understanding the relationship between the electronic transition and atomic vibration.

Phase transition mechanism and bandgap engineering of Sb2S3 at gigapascal pressures

Earth-abundant antimony trisulfide (Sb2S3), or simply antimonite, is a promising material for capturing natural energies like solar power and heat flux. The layered structure, held up by weak van-der Waals forces, induces anisotropic behaviors in carrier transportation and thermal expansion. Here, we used stress as mechanical stimuli to destabilize the layered structure and observed the structural phase transition to a three-dimensional (3D) structure. We combined in situ x-ray diffraction (XRD), Raman spectroscopy, ultraviolet-visible spectroscopy, and first-principles calculations to study the evolution of structure and bandgap width up to 20.1 GPa. The optical band gap energy of Sb2S3 followed a two-step hierarchical sequence at approximately 4 and 11 GPa. We also revealed that the first step of change is mainly caused by the redistribution of band states near the conduction band maximum. The second transition is controlled by an isostructural phase transition, with collapsed layers and the formation of a higher coordinated bulky structure. The band gap reduced from 1.73 eV at ambient to 0.68 eV at 15 GPa, making it a promising thermoelectric material under high pressure.

Structural, Vibrational, and Electronic Properties of 1D-TlInTe2 under High Pressure: A Combined Experimental and Theoretical Study

Analogous to 2D layered transition-metal dichalcogenides, the TlSe family of quasi-one dimensional chain materials with the Zintl-type structure exhibits novel phenomena under high pressure. In the present work, we have systematically investigated the high-pressure behavior of TlInTe₂ using Raman spectroscopy, synchrotron X-ray diffraction (XRD), and transport measurements, in combination with first principles crystal structure prediction (CSP) based on evolutionary approach. We found that TlInTe₂ undergoes a pressure-induced semiconductor-to-semimetal transition at 4 GPa, followed by a superconducting transition at 5.7 GPa (with T_c = 3.8 K). An unusual giant phonon mode (A_g) softening appears at ∼10-12 GPa as a result of the interaction of optical phonons with the conduction electrons. The high-pressure XRD and Raman spectroscopy studies reveal that there is no structural phase transitions observed up to the maximum pressure achieved (33.5 GPa), which is in agreement with our CSP calculations. In addition, our calculations predict two high-pressure phases above 35 GPa following the phase transition sequence as I4/mcm (B37) → Pbcm → Pm3̅m (B2). Electronic structure calculations suggest Lifshitz (L1 & L2-type) transitions near the superconducting transition pressure. Our findings on TlInTe₂ open up a new avenue to study unexplored high-pressure novel phenomena in TlSe family induced by Lifshitz transition (electronic driven), giant phonon softening, and electron-phonon coupling.

Pressure-induced isostructural electronic topological transitions in 2H-MoTe2: x-ray diffraction and first-principles study

Synchrotron x-ray diffraction measurements on powder 2H-MoTe₂ (P6₃/mmc) up to ∼46 GPa have been performed along with first-principles based density functional theoretical analysis to probe the isostructural transition in low pressure regime and two electronic topological transitions (ETT) of Lifshitz-type in high pressure regime. The low pressure isostructural transition at ∼7 GPa is associated with the lattice parameter ratio c/a anomaly and the change in the compressibility of individual layers. The pressure dependence of the volume by linearizing the Birch-Murnaghan equation of state as a function of Eulerian strain shows a clear change of the bulk modulus at the ETT pressure of ∼20 GPa. The minimum of c/a ratio around 32 GPa is associated with the change in topology of electron pockets marked as second ETT of Lifshitz-type. We do not observe any structural transition up to the maximum applied pressure of ∼46 GPa under quasi-hydrostatic condition.

Sb2S3 Nanoparticles Anchored or Encapsulated by the Sulfur-Doped Carbon Sheet for High-Performance Supercapacitors

The specific capacitance and energy density of antimony trisulfide (Sb₂S₃)@carbon supercapacitors (SCs) have been limited and are in need of significant improvement. In this work, Sb₂S₃ nanoparticles were selectively encapsulated or anchored in a sulfur-doped carbon (S-carbon) sheet depending on the use of microwave-assisted synthesis. The microwave-triggered Sb₂S₃ nanoparticle growth resulted in core-shell hierarchical spherical particles of uniform diameter assembled with Sb₂S₃ as the core and an encapsulated S-carbon layer as the shell (Sb₂S₃-M@S-C). Without the microwave mediation, the other nanostructure was found to comprise fine Sb₂S₃ nanoparticles widely anchored in the S-carbon sheet (Sb₂S₃-P@S-C). Structural and morphological analyses confirmed the presence of encapsulated and anchored Sb₂S₃ nanoparticles in the carbon. These two materials exhibited higher specific capacitance values of 1179 (0 to +1.0 V) and 1380 F·g^-1 (-0.8 to 0 V) at a current density of 1 A·g^-1, respectively, than those previously reported for Sb₂S₃ nanomaterials in considerable SCs. Furthermore, both materials exhibited outstanding reversible capacitance and cycle stability when used as SC electrodes while retaining over 98% of the capacitance after 10 000 cycles, which indicates their long-term stability. Furthermore, a hybrid Sb₂S₃-M@S-C/Sb₂S₃-P@S-C device was designed, which delivers a remarkable energy density of 49 W·h·kg^-1 at a power density of 2.5 kW·kg^-1 with long-term cycle stability (94% over 10 000 cycles) and is comparable to SCs in the recent literature. Finally, a light-emitting diode (LED) panel comprising 32 LEDs was powered using three pencil-type hybrid SCs in series.

Experimental Observation of the High Pressure Induced Substitutional Solid Solution and Phase Transformation in Sb2S3

The substitutional solid solutions composed of group VA-VIA nonmetallic elements has attracted considerable scientific interest since they provide a pressure-induced route to search for novel types of solid solutions with potential applications. Yet, the pressure-induced solid solution phase is unprecedented in the sulfide family. In this paper, the structural behavior of antimony trisulfide, Sb₂S₃, has been investigated in order to testify whether or not it can also be driven into the substitutional solid solution phase by high pressures. The experiments were carried out by using a diamond anvil cell and angle dispersive synchrotron X-ray diffraction up to 50.2 GPa at room temperature. The experimental results indicate that Sb₂S₃ undergoes a series of phase transitions at 5.0, 12.6, 16.9, 21.3, and 28.2 GPa, and develops ultimately into an Sb-S substitutional solid solution, which adopts a body-centered cubic disordered structure. In this structure, the Sb and S atoms are distributed randomly on the bcc lattice sites with space group Im-3m. The structural behavior of Sb₂S₃ is tentatively assigned by comparison within the A₂B₃ (A = Sb, Bi; B = Se, Te, S) series under high pressures.

Structural properties of Sb2S3 under pressure: evidence of an electronic topological transition

High-pressure Raman spectroscopy and x-ray diffraction of Sb₂S₃ up to 53 GPa reveals two phase transitions at 5 GPa and 15 GPa. The first transition is evidenced by noticeable compressibility changes in distinct Raman-active modes, in the lattice parameter axial ratios, the unit cell volume, as well as in specific interatomic bond lengths and bond angles. By taking into account relevant results from the literature, we assign these effects to a second-order isostructural transition arising from an electronic topological transition in Sb₂S₃ near 5 GPa. Close comparison between Sb₂S₃ and Sb₂Se₃ up to 10 GPa reveals a slightly diverse structural behavior for these two compounds after the isostructural transition pressure. This structural diversity appears to account for the different pressure-induced electronic behavior of Sb₂S₃ and Sb₂Se₃ up to 10 GPa, i.e. the absence of an insulator-metal transition in Sb₂S₃ up to that pressure. Finally, the second high-pressure modification appearing above 15 GPa appears to trigger a structural disorder at ~20 GPa; full decompression from 53 GPa leads to the recovery of an amorphous state.