Ferroelastic phase transitions—well-known results and new perspectives

Abstract

Chapter 2 provides an overview of the thermodynamics governing ferroelastic and antiferroelectric systems and formulates some open questions on these topics. Ferroelastic materials are defined by the reversible phase transition they undergo from a high-symmetry (high-temperature) paraelastic phase to a low-symmetry (low-temperature) ferroelastic phase, giving rise to spontaneous strain. If the two phases are group–subgroup related, this transition is described with a high accuracy by Landau-type theories, where coupling between order parameters and spontaneous strain is considered. Landau–Ginzburg theory can also be used to discuss the effects from inhomogeneous structures such as domains, domain walls or precursor structures. In contrast to the ferroelastic phase transitions that give rise to macroscopic tensors coupled to macroscopic fields, the criteria defining antiferroelectric phase transitions (that are also observed in ferroelastic materials) are still under discussion due to the absence of specific symmetry properties characterizing their existence. Recent approaches based on Landau-type theories tackle this issue.