An Ising-like model of stacking-sequence polytypism in ABX3compounds

Abstract
The crystallographic structure of a large class of ABX3 compounds can be characterised by the stacking sequences of face- and corner-sharing BX6-octahedra chains on a hexagonal lattice. Many different polytypes described by this type of stacking have been observed in these and related materials. An axial Ising-type model free energy that includes terms linear and cubic in the pseudo-spin variable is proposed to describe the possible phases which result from interactions between octahedra. The model is also shown to account for the increase in corner-sharing sequences with increasing pressure observed in, for example, CsBF3B=Mn, Fe, Co, Ni.
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