Boundary Conditions for Shape Memory in Ceramic Material Systems

Piezoelectric ceramics have excellent transduction capability in elastoelectric conversion and are widely used as both sensors and actuators for smart materials and systems. The very high authority in actuation (tons/in2) is limited in application by the very short throw (strains = 10-3) and there is urgent need to improve this strain capability. Since the polarization related piezoelectric and electrostriction constants in perovskites have a very limited range, to improve strain it is necessary to switch larger values of polarization. In this paper, phase change and domain switching systems which mimic the high strain of the metallic martensite shape memory alloys will be reviewed. Characteristic features necessary to ensure electrical control of the shape will be discussed and illustrated by three different families of perovskites. It is speculated that at very high switching speeds the electrostrictive domain strain may become 'uncoupled' from the polarization and evidence that this occurs in bismuth titanate is presented.