ABX3formule

ABX3 formula denotes a class of compounds composed of an A-site cation, a B-site cation, and X an anion, combined in a 1:1:3 ratio. The A and B cations differ in size and charge, and X is an anion such as oxide O2− or halide X−. The ABX3 composition is widely used to describe perovskite-related structures in solid-state chemistry and materials science.

In many ABX3 compounds, particularly perovskites, BX6 octahedra form a three-dimensional framework with corner-sharing octahedra. The larger A cation sits in cuboctahedral cavities between the octahedra. The geometry can be ideal cubic but often shows distortions due to ionic radii differences; the tolerance factor t is used to predict stability: t = (rA + rX)/√2(rB + rX). Values near 1 favor a cubic arrangement; smaller values lead to tilting and lower symmetry.

Oxide ABX3 perovskites (X = O2−) include SrTiO3, BaTiO3, and related compounds; they exhibit ferroelectricity, dielectric properties, and catalytic activity. Halide ABX3 perovskites (X = halide) have gained prominence in optoelectronics, notably CsPbI3, FAPbBr3, and MAPbI3, used in solar cells and light-emitting devices. The A cation can be inorganic (Cs+, Sr2+) or organic (methylammonium MA+, formamidinium FA+), while B is typically a transition metal in oxides or a metal like Pb2+ or Sn2+ in halides.

Synthesis commonly involves high-temperature solid-state methods for oxides; halide ABX3 materials are often prepared by solution processing, crystallization, and deposition techniques. Their properties depend on composition, cation size, and X type, enabling tunable band gaps, dielectric performance, and stability concerns such as moisture sensitivity in halide variants and tolerance to ionic substitution.