Ideal halide perovskites adopt a cubic ABX₃ lattice (space group Pm3̅m), but most undergo distortions (to tetragonal or orthorhombic symmetry) as a function of temperature, composition and ionic sizes. In the cubic form the B cation is octahedrally coordinated (6-fold) by X, and the A cation sits in a 12-fold cuboctahedral site formed by the vertices of eight adjacent BX₆ octahedra. (This can be quantified by the Goldschmidt tolerance factor t = (r_A + r_X) / √2(r_B + r_X), which must be ≈0.8–1 for a stable perovskite.)

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