PARAMETERIZATION OF THE CRYSTAL STRUCTURES OF CENTROSYMMETRIC ZONE-BOUNDARY-TILTED PEROVSKITES: AN ANALYSIS IN TERMS OF SYMMETRY-ADAPTED BASIS-VECTORS OF THE CUBIC ARISTOTYPE PHASE

摘要: The methods of group theory have been used to decompose the crystal structures centrosymmetric perovskites, ABX 3 , that exhibit zone-boundary tilting BX 6 octahedra. For fourteen space-groups consistent with these phenomena, associated are decomposed in terms magnitudes an appropriate set symmetry-adapted basis-vectors primitive cubic aristotype phase perovskite at high-symmetry points on surface Brillouin zone. advantage this parameterization is twofold; firstly, octahedron tilt angles can be determined precisely and independently effects distortion, secondly, degrees freedom required by structure rigorously derived. method outlined using results a neutron-diffraction investigation CaTiO space Pbnm example where structural found one less than group. Full very simply utilised decomposition other thirteen tabulated. advantages decomposing perovskite-structured phases way further illustrated temperature dependence KCaF between 4.2 542 K.