| The works reported in this thesis address three basic problem areas which are associated with different practical uses of ferroelectric type materials for electromechanical actuator applications.; In a low strain precision system such as the Lead Magnesium Niobate: Lead Titanate (PMN:PT) family of electrostrictors, precise reproducibility of the electrostrictive strain and the absence of dielectric hysteresis are essential attractions for the use of these materials. Ageing, which is the slow stabilization of an existing ferroic internal structure, is a phenomenon which effects all normal ferroelectric ceramics, and destroys the reproducibility of electrically induced strain in these systems. In this study, it has been shown that by careful fabrication using high purity oxides, 0.9PMN0.1PT ceramic can be made which shows no ageing. Furthermore, by deliberate doping with Manganese oxide (MnO), ageing can be reintroduced. Through a sequence of studies on isothermal ageing and on ageing under bias fields, the nature of the effective internal bias field associated with ordering the defects induced by doping has been explored and the nature of the ageing process delineated.; For very high strain actuators, it is necessary to make use of the spontaneous strains induced by ferroic phase changes, or by domain switching in a spontaneous polarized state. For these systems, the strain versus field relations are hysteretic but in certain cases the strain is a unique function of polarization, so that charge control of dimensions is now possible. Systems explored in this work included paraelectric: ferroelectric switching above the Curie temperature in single crystal BaTiO{dollar}sb3{dollar} (0.36% strain), 90{dollar}spcirc{dollar} domain switching in single crystal BaTiO{dollar}sb3{dollar} (0.65% strain), antiferroelectric: ferroelectric switching in modified Lead Zirconate Titanate Stannate ceramics (0.85% strain) and ferroelectric switching of morphotropic phase boundary compositions in the PLZT ceramic family (0.54% maximum longitudinal strain). Charge control, coercivity and stability of the remanent strain have been explored and the fatigue effects associated with repeated switching examined.; The kinetics of field induced polarization and strain have been investigated for Pb(Ti,Zr)O{dollar}sb3{dollar} family of ferroelectrics, and for the phase switching in the modified Lead Zirconate Titanate Stannate antiferroelectric ceramics. For both families, switching can be accomplished in microsecond switching times under high fields and kinetics of switching does not limit potential applications. |
