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. 2022 Jun 21;12(28):18102-18106.
doi: 10.1039/d2ra02114e. eCollection 2022 Jun 14.

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

Ao Zhang  1   2 , Yaqian Dan  1 , Han Liu  1   2 , Siyuan Liu  3 , Jincheng Yue  1 , Junda Li  1 , Yanping Huang  1 , Yanhui Liu  1 , Tian Cui  1
Affiliations

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

Ao Zhang et al. RSC Adv. .

Abstract

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.

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Conflict of interest statement

There are no conflicts to declare.

Figures

Fig. 1
Fig. 1. Relative enthalpies of formation of Co–As phases with respect to elemental cobalt and arsenic solids. The convex hulls connecting stable phases (solid star) are shown by solid lines. Metastable phases are shown by open star.
Fig. 2
Fig. 2. Predicted pressure-composition phase diagram of Co–As crystal phases. Cyan and red colours represent the metallic and non-metallic phases, respectively. The solid (dash) lines represent stable (metastable) phases.
Fig. 3
Fig. 3. Structures of predicted Co–As system for (a) Co2As-Pnma at 1.28 GPa; (b) CoAs2-Pnnm at 74.5 GPa, and (c) CoAs3-C2/m at 45.7 GPa. The blue and pink spheres are Co atoms and As atoms, respectively.
Fig. 4
Fig. 4. Phonon dispersion relations and phonon density of states projected on Co atoms and As atoms for (a) Co2As-Pnma at 1.28 GPa (b) CoAs2-Pnnm at 74.5 GPa, and (c) CoAs3-C2/m at 45.7 GPa.
Fig. 5
Fig. 5. Electronic band structure and the projected electronic DOS on Co atoms and As atoms for (a) Co2As-Pnma at 1.28 GPa; (b) CoAs2-Pnnm at 74.5 GPa; (c) CoAs3-C2/m at 45.7 GPa, and (d) CoAs3-C2/m at 48 GPa. Note that Zero energy is at the Fermi level.
Fig. 6
Fig. 6. Contours of the ELF for the structures of (a) Co2As-Pnma at 1.28 GPa; (b) CoAs2-Pnnm at 74.5 GPa, and (c) CoAs3-C2/m at 45.7 GPa with isosurface of 0.8.
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