Ferroelasticity, pseudoelasticity and shape memory effect in Pb3(PO4)2

We have found that ferroelastic Pb3(PO4)2 crystal exhibits pseudoelasticity and shape-memory effect which have been commonly observed in b.c.c. based alloys. Single crystals of Pb3(PO4)2 are observed to be deformed reversibly beyond ordinary elastic limit of ionic materials under the application of stress of specific type. The large deformation was found to be realized by the change in domain structure associated with the variants of the ferroelastic phase. Effective elastic constant (pseudoelastic constant) of Pb3(PO4)2 determined from the measurement of stress-strain curve of a bulk sample was found to be 10−3 times smaller than the intrinsic elastic constant of this material. By some aging treatment, the bistable state of domain structure was realized, which is interpreted to be a kind of two-way shape memory effect.