Ilias Efthimiopoulos

Sb2Se3 under pressure

Selected members of the A2B3 (A = Sb, Bi; B = Se, Te) family are topological insulators. The Sb2Se3 compound does not exhibit any topological properties at ambient conditions; a recent high-pressure study, however, indicated that pressure transforms Sb2Se3 from a band insulator into a topological insulator above ~2 GPa; in addition, three structural transitions were proposed to occur up to 25 GPa. Partly motivated by these results, we have performed x-ray diffraction and Raman spectroscopy investigations on Sb2Se3 under pressure up to 65 GPa. We have identified only one reversible structural transition: the initial Pnma structure transforms into a disordered cubic bcc alloy above 51 GPa. On the other hand, our high-pressure Raman study did not reproduce the previous results; we attribute the discrepancies to the effects of the different pressure transmitting media used in the high-pressure experiments. We discuss the structural behavior of Sb2Se3 within the A2B3 (A = Sb, Bi; B = Se, Te) series.

Sb 2 Se 3 under pressure

Selected members of the A2B3 (A = Sb, Bi; B = Se, Te) family are topological insulators. The Sb2Se3 compound does not exhibit any topological properties at ambient conditions; a recent high-pressure study, however, indicated that pressure transforms Sb2Se3 from a band insulator into a topological insulator above ~2 GPa; in addition, three structural transitions were proposed to occur up to 25 GPa. Partly motivated by these results, we have performed x-ray diffraction and Raman spectroscopy investigations on Sb2Se3 under pressure up to 65 GPa. We have identified only one reversible structural transition: the initial Pnma structure transforms into a disordered cubic bcc alloy above 51 GPa. On the other hand, our high-pressure Raman study did not reproduce the previous results; we attribute the discrepancies to the effects of the different pressure transmitting media used in the high-pressure experiments. We discuss the structural behavior of Sb2Se3 within the A2B3 (A = Sb, Bi; B = Se, Te) series.

High-pressure studies of Bi2S3.

The high-pressure structural and vibrational properties of Bi2S3 have been probed up to 65 GPa with a combination of experimental and theoretical methods. The ambient-pressure Pnma structure is found to persist up to 50 GPa; further compression leads to structural disorder. Closer inspection of our structural and Raman spectroscopic results reveals notable compressibility changes in specific structural parameters of the Pnma phase beyond 4-6 GPa. By taking the available literature into account, we speculate that a second-order isostructural transition is realized near that pressure, originating probably from a topological modification of the Bi2S3 electronic structure near that pressure. Finally, the Bi(3+) lone-electron pair (LEP) stereochemical activity decreases against pressure increase; an utter vanishing, however, is not expected until 1 Mbar. This persistence of the Bi(3+) LEP activity in Bi2S3 can explain the absence of any structural transitions toward higher crystalline symmetries in the investigated pressure range.

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.

Multiple pressure-induced transitions in HgCr2S4

We have performed combined experimental and theoretical high-pressure investigations on magnetoelectric HgCr2S4 spinel. Overall, HgCr2S4 exhibits three reversible structural transitions under pressure: the starting Fd-3m phase adopts a tetragonal I41/amd structure at 20 GPa, an orthorhombic distortion occurs above 26 GPa, whereas a third structural transition takes place beyond 37 GPa. During the Fd-3m to I41/amd structural transition, HgCr2S4 experiences a volume change of 4% which is unexpected from space group symmetry considerations alone. Furthermore, the Fd-3m to I41/amd transformation appears to be concomitant with an insulator-to-metal transition whereas compression of HgCr2S4 leads to a gradual suppression of its ferromagnetism.

Pressurizing the HgCr2Se4 spinel at room temperature

The cubic HgCr2Se4 spinel undergoes two structural transitions upon pressure increase. Initially, the ambient-pressure Fd-3m phase transforms into a tetragonal I41/amd structure above 15 GPa. We speculate that this Fd-3m-I41/amd transition is accompanied by an insulator-to-metal transition, resulting in the vanishing of the Raman signal after the structural transformation. Further compression of HgCr2Se4 leads to structural disorder beyond 21 GPa. Our spin-resolved band structure calculations reveal significant changes in the electronic structure of HgCr2Se4 after the Fd-3m-I41/amd transition, whereas the ferromagnetic interactions are found to dominate in both structures.

Evidence for a pressure-induced spin transition in olivine-type

We present a combination of first-principles and experimental results regarding the structural and magnetic properties of olivine-type LiFePO

\mathrm{LiFePO_{4}}

_4

triphylite

under pressure. Our investigations indicate that the starting

Pressure-induced transition in the multiferroic CoC r 2 O 4 spinel

Pbnm