Monoclinic–orthorhombic first-order phase transition in K₂ZnSi₅O₁₂ leucite analogue; transition mechanism and spontaneous strain analysis

Abstract Hydrothermally synthesised K 2 ZnSi 5 O 12 has a polymerised framework structure with the same topology as leucite (KAlSi 6 , tetragonal I 4 1 / ), which two tetrahedrally coordinated Al 3+ cations replaced by Zn 2+ and Si 4+ . At 293 it cation-ordered P c monoclinic lattice parameters = 13.1773(2) Å, b 13.6106(2) 13.0248(2) Å β 91.6981(9)°. This is isostructural MgSi first analogue characterised. With increasing temperature, transforms reversibly to orthorhombic Pbca. transition takes place over temperature range 848−863 where both phases coexist; there an ~1.2% increase in unit cell volume between 843 ( ) 868 Pbca characteristic of first-order, displacive, ferroelastic phase transition. Spontaneous strain analysis defines symmetry- non-symmetry related changes shows that mechanism weakly order; two-phase region consistent being strain-related martensitic