Equivalent least deformation orientation variants by a phase transition between two structures with subgroups of the same point group

Abstract

In a phase transition occurring between a structure of a subgroup 1 and another of a subgroup 2, both subgroups of the same point group, the lattice (or unit cell) transformation from one variant of the parent structure to one variant of the daughter structure generally depends on the really appearing variant of the daughter phase. Then all the orientation variants of the daughter structure may not be equivalent from the point of view of the lattice (or unit cell) transformation. It can be expected that the least deformation variant(s) occur(s) preferentially. Generally several of these least deformation variants are equivalent for a transformation from one variant of the parent phase. Their number can be easily determined. When such a transformation occurs from structure 1 to structure 2 and back to structure 1 new variants of structure 1 may occur, with a probability that can be determined in each case. After several direct and reverse phase transitions some minimization of the free energy may occur for real crystals, giving rise to a possible memory effect.

Key Words:

• Subgroup-subgroup phase transition
• memory effect