New High-Pressure Phases of MoSe2 and MoTe2
Abstract
Three Mo-based transition metal dichalcogenides MoS2, MoSe2 and MoTe2 share at ambient conditions the same structure 2Hc, consisting of layers where Mo atoms are surrounded by six chalcogen atoms in trigonal prism coordination. The knowledge of their high-pressure behaviour is, however, limited, particularly in case of MoSe2 and MoTe2. The latter materials do not undergo a layer-sliding transition 2Hc → 2Ha known in MoS2 and currently no other stable phase besides 2Hc is known in these systems at room temperature. Employing evolutionary crystal structure prediction in combination with ab initio calculations we study the zero-temperature phase diagram of both materials up to Mbar pressures. We find a tetragonal phase with space group P4/mmm, previously predicted in MoS2, to become stable in MoSe2 at 118 GPa. In MoTe2 we predict at 50 GPa a transition to a new layered tetragonal structure with space group I4/mmm, similar to CaC2, where Mo atoms are surrounded by eight Te atoms. The phase is metallic already at the transition pressure and becomes a good metal beyond 1 Mbar. We discuss chemical trends in the family of Mo-based transition metal dichalcogenides and suggest that MoTe2 likely offers the easiest route towards the post-2H phases.
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