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The pressure-induced phase transition of bismuth telluride, Bi 2 Te 3 , has been studied by synchrotron x-ray diffraction measurements at room temperature using a diamond-anvil cell (DAC) with loading pressures up to 29.8 GPa. We found a high-pressure body-centered cubic (bcc) phase in Bi 2 Te 3 at 25.2 GPa, which is denoted as phase IV, and this phase apperars above 14.5 GPa.Upon releasing the pressure from 29.8 GPa, the diffraction pattern changes with pressure hysteresis. The original rhombohedral phase is recovered at 2.43 GPa. The bcc structure can explain the phase IV peaks. We assumed that the structural model of phase IV is analogous to a substitutional binary alloy; the Bi and Te atoms are distributed in the bcc-lattice sites with space group Im3m.The results of Rietveld analysis based on this model agree well with both the experimental data and calculated results. Therefore, the structure of phase IV in Bi 2 Te 3 can be explained by a solid solution with a bcc lattice in the Bi−Te (60 atomic% tellurium) binary system.

The Dirac semimetal PdTe2 was recently reported to be a type-I superconductor (Tc =1.64 K, µ0Hc(0) = 13.6 mT) with unusual superconductivity of the surface sheath. We here report a high-pressure study, p ≤ 2.5 GPa, of the superconducting phase diagram extracted from acsusceptibility and transport measurements on single crystalline samples. Tc(p) shows a pronounced non-monotonous variation with a maximum Tc =1.91 K around 0.91 GPa, followed by a gradual decrease to 1.27 K at 2.5 GPa. The critical field of bulk superconductivity in the limit T → 0, Hc(0, p), follows a similar trend and consequently the Hc(T, p)-curves under pressure collapse on a single curve: Hc(T, p) = Hc(0, p)[1 − (T /Tc(p)) 2 ]. Surface superconductivity is robust under pressure as demonstrated by the large superconducting screening signal that persists for applied dc-fields Ha > Hc. Surprisingly, for p ≥ 1.41 GPa the superconducting transition temperature at the surface T S c is larger than Tc of the bulk. Therefore surface superconductivity may possibly have a non-trivial nature and is connected to the topological surface states detected by ARPES. We compare the measured pressure variation of Tc with recent results from band structure calculations and discuss the importance of a Van Hove singularity.

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Infrared vibrational absorption spectra are measured for yttrium trihydride at room temperature and pressures up to 30 GPa. The spectral change that begins near 12 GPa is interpreted in terms of a hcp-fcc structural transition, which agrees with previous x-ray diffraction measurements. For the hydrogen vibrations in the low-pressure hcp phase, the mode Grüneisen parameters are derived from the observed peak frequency shifts with pressure and the reported bulk modulus. The value of 1.91 for the octahedral-site vibration is three times larger than those for the tetrahedral-site vibrations, suggesting hybridization between the hydrogen 1s and yttrium 4d orbitals at the octahedral site. The infrared transmission spectra collapse when the high-pressure fcc phase is compressed beyond 23 GPa. The band gap abruptly closes without a structural change in the fcc metal lattice. The experimental results are in contrast to the previous theoretical calculations predicting the electronic transition either with hcp-fcc structural change or in the hcp low-pressure phase without structural change. The transition mechanism is still inconclusive.

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The location of the liquidus in the low-pressure crystalline phase of SnI(4) was determined utilizing in situ x-ray diffraction measurements under pressures up to approximately 3.5 GPa. The liquidus is not well fitted to a monotonically increasing curve such as Simon's equation, but breaks near 1.5 GPa and then becomes almost flat. The results are compared to those from molecular dynamics simulations. Ways to improve the model potential adopted in the simulations are discussed.