Tilting structures in perovskites

Thirty five low-symmetry tilting phases of the octahedra in which the atoms located at the initial octahedral position remain equivalent are derived for the perovskite structure at the k₁₀(X), k₁₁(M), and k₁₃(R) points of the Brillouin zone. For each low-symmetry phase, structural data are presented and a relationship between the atomic displacements and the order parameters is deduced. All the low-symmetry phases can be obtained by considering only one or two order parameters.