The Abrahams - Kurtz - Jamieson relationship, derived for ferroelectrics, has been extended to ferroelastic materials. It is shown that such relationships often shed light on the structural mechanisms that cause ferroic distortions. The ferroelastic properties of the isostructural compounds NdNbO4 and NdTaO4 are considered, and it is shown that the ferroelastic transition temperatures and saturated spontaneous strain components are, respectively, proportional to the square of and linearly proportional to the saturated spontaneous displacements of the Nb5+ and Ta5+ ions. © 1983.
