Phase stability and pressure-induced structural transitions at zero temperature inZnSiO3 andZn2SiO4

Abstract

Using density functional total energy calculations the structural phasestability and pressure-induced structural transition in different polymorphs ofZnSiO3 andZn2SiO4 have been studied. Among the considered monoclinic phase with space groups(P 21/c) and(C 2/c), rhombohedral and orthorhombic (Pbca) modifications the monoclinic phase(P 21/c) ofZnSiO3 is found to be the most stable one. At high pressure monoclinicZnSiO3 (C 2/c) can co-exist with orthorhombic (Pbca) modification. Differences in equilibrium volumeand total energy of these two polymorphs are very small, which indicates thatit is relatively easier to transform between these two phases by temperature,pressure or chemical composition. It can also explain the experimentally establishedresult of metastability of the orthorhombic phase under all conditions. Thefollowing sequence of pressure-induced structural phase transitions is found forZnSiO3 polymorphs: monoclinic monoclinic rhombohedral . Among the rhombohedral (), tetragonal , orthorhombic (Pbca), orthorhombic (Imma), cubic and orthorhombic (Pbnm) modifications ofZn2SiO4, the rhombohedral phase is found to be the ground state. For this chemical composition ofzinc silicate the following sequence of structural phase transitions is found: rhombohedral tetragonal orthorhombic orthorhombic (Imma) cubic orthorhombic (Pbnm). Based on the analogy of crystal structures ofmagnesium and zinc silicates and using the lattice and positional parameters ofMg2SiO4 as input, structuralproperties of spinel Zn2SiO4 have also been studied.