High pressure stability of the monosilicides of cobalt and the platinum group elements

The high pressure stability of CoSi, RuSi, RhSi, PdSi, OsSi, IrSi and PtSi was investigated by static first-principles calculations up to 300 GPa at 0 K. As found experimentally, at atmospheric pressure, CoSi, RuSi and OsSi were found to adopt the cubic epsilon-FeSi structure (P2(1)3) whereas RhSi, PdSi, IrSi and PtSi were found to adopt the orthorhombic MnP (Pnma) structure. At high pressure, CoSi, RuSi and OsSi show a phase transition to the CsCl structure (Pm (3) over barm) structure at 270 GPa, 7 GPa and 6 GPa respectively. RhSi and IrSi were found to transform to an e-FeSi structure at 10 GPa and 25 GPa. For PdSi and PtSi, a transformation from the MnP structure to the tetragonal CuTi structure (P4/nmm) occurs at 13 GPa and 20 GPa. The pressure dependence of the electronic density of states reveals that RuSi and OsSi are semiconductors in the epsilon-FeSi structure and become metallic in the CsCl structure. RhSi and IrSi are metals in the MnP structure and become semimetals in their high pressure epsilon-FeSi form. CoSi in the epsilon-FeSi configuration is a semimetal. PdSi and PtSi remain metallic throughout up to 300 GPa. (C) 2014 Elsevier B.V. All rights reserved.