Structural phase transition and potential superconductivity initiated by pressure-driven in 1T-CrSe2.

The exploration of the superconducting properties of antiferromagnetic parent compounds containing transition metals under pressure provides a unique idea for finding and designing superconducting materials with better performance. In this paper, the close relationship between the possible superconductivity and structure phase transition of the typical van der Waals layered material 1T-CrSe2induced by pressure is studied by means of electrical transport and x-ray diffraction for the first time. We introduce the possibility of pressure-induced superconductivity at 20 GPa, with a criticalTcof approximately at 4 K. The superconductivity persists up to the highest measured pressure of 70 GPa, with a maximumTc∼ 5 K at 24 GPa. We observed a structure phase transition fromP-3m1 toC2/mspace group in the range of 9.4-11.7 GPa. The results show that the structural phase transition leads to the metallization of 1T-CrSe2and the further pressure effect makes the superconductivity appear in the new structure. The material undergoes a transition from a two-dimensional layered structure to a three-dimensional structure under pressure. This is the first time that possible superconductivity has been observed in 1T-CrSe2.

Phase transition and electronic properties of Co-As binary compounds at high pressure.

New stable stoichiometries in the Co-As system are investigated up to 100 GPa by the CALYPSO structure prediction method. In particular, we found three novel stable compounds of Co2As-Pnma, CoAs2-Pnnm, and CoAs3-C2/m at high pressure. According to the theoretical electronic band structures, the structures of Co2As-Pnma, CoAs2-Pnnm, and CoAs3-C2/m have metallic characters, and a pressure-induced electronic topological transition was found in CoAs3-C2/m, which is not shown in other stoichiometries of the Co-As system. The calculated results of the electron localization function show that there are polar covalent bond interactions between Co atoms and As atoms in CoAs2-Pnnm and CoAs3-C2/m. The present results can be helpful for understanding diverse structures and properties of Co-As binary compounds under high pressure.

First-Principles Study of High-Pressure Phase Stability and Electron Properties of Be-P Compounds.

New, stable stoichiometries in Be-P systems are investigated up to 100 GPa by the CALYPSO structure prediction method. Along with the BeP2-I41/amd structure, we identify two novel compounds of Be3P2-P-421m and Be3P2-C2/m. It should be noted that the Be-P compounds are predicted to be energetically unfavorable above 40 GPa. As can be seen, interesting structures may be experimentally synthesizable at modest pressure. Our results indicate that at 33.2 GPa, the most stable ambient-pressure tetragonal Be3P2-P-421m transitions to the monoclinic Be3P2-C2/m structure. Moreover, the predicted Be3P2-P-421m and Be3P2-C2/m phases are energetically favored compared with the Be3P2-Ia-3 structure synthesized experimentally. Electronic structure calculations reveal that BeP2-I41/amd, Be3P2-P-421m, and Be3P2-C2/m are all semiconductors with a narrow band gap. The present findings offer insight and guidance for exploration toward further fundamental understanding and potential applications in the semiconductor field.