New High-Pressure Phases of MoSe and MoTe
arXiv:1611.07757 · doi:10.1103/PhysRevB.95.054105
Abstract
Three Mo-based transition metal dichalcogenides MoS, MoSe and MoTe share at ambient conditions the same structure 2H, 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 MoSe and MoTe. The latter materials do not undergo a layer-sliding transition 2H 2H known in MoS and currently no other stable phase besides 2H is known in these systems at room temperature. Employing evolutionary crystal structure prediction in combination with \textit{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 \textit{P4/mmm}, previously predicted in MoS, to become stable in MoSe at 118 GPa. In MoTe we predict at 50 GPa a transition to a new layered tetragonal structure with space group \textit{I4/mmm}, similar to CaC, 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 MoTe likely offers the easiest route towards the post-2H phases.
6 pages, 9 figures