Phase stability and pressure-induced structural transitions in ZnSiO3 and Zn2SiO4

Using density functional total energy calculations the structural phase stability and pressureinduced structural transition in different polymorphs of ZnSiO3 and Zn2SiO4 have been studied. Among the considered possible ZnSiO3 polymorphs, monoclinic phase with space group P21/c is found to be the most stable one. At high pressure monoclinic ZnSiO3 (C2/c) can coexist with orthorhombic (Pbca) modification. Difference in equilibrium volume and total energy of these two polymorphs are very small, which indicates that fluctuation of pressure or temperature can be sufficient to cause transformation between them. It can also explain the experimentally established result of metastability of the orthorhombic phase under all conditions. The following sequence of pressure induced structural phase transitions are found for ZnSiO3 polymorphs: monoclinic (P21/c) → monoclinic (C2/c) → rhombohedral ( 3 R ). Among the Zn2SiO4 polymorphs considered, rhombohedral phase is found to be the ground state. For this chemical composition of the zinc silicates the following sequence of structural phase transitions is found: rhombohedral ( 3 R ) → tetragonal ( d I 2 4 ) → orthorhombic (Pbca) → orthorhombic (Imma) → cubic ( m Fd3 ) → orthorhombic (Pbnm)→monoclinic (P21/n). Based on the analogy of crystal structures of magnesium and zinc silicates and using the lattice and positional parameters of MgSiO3 and Mg2SiO4 as input, structural properties of corundum ZnSiO3 and spinel Zn2SiO4 have also been studied.