School of Engineering and Materials Science
Research Student Awards
PhD Thesis: Domain switching dynamics in ferroelastic and ferroelastic/ferroelectric perovskites
Author: VIOLA, Giuseppe
Supervisor(s): Mike Reece
A comprehensive study of domain switching process in different ferroelastic and ferroelastic/ferroelectric perovskite structured ceramics has been performed.
Compression tests were carried out to characterise the ferroelastic properties, such as coercive stress, hysteresis loop and irreversible strain. Creep experiments were performed to study the domain switching time dependence at different stress levels. Domain switching kinetics during creep was characterised by implementing a rate model, based on thermal activation rate theory, which allowed the activation volume to be estimated. A Rayleigh-type analysis was performed to study the effects of stress amplitude, loading rate, temperature and composition on ferroelastic switching. Rayleigh-type relationships were proposed to fit the results and the rate model developed was applied to quantify the effect of the loading rate on the Rayleigh loops. Alternative methodologies were developed to assess the effects of rate and temperature on the coercive stress. A further application of the rate model provided an estimation of the activation parameters (volume and enthalpy). In PZT 5A at the coercive field the activation volume was calculated to be 2.44nm3, with a reasonable consistency with the value obtained from creep tests (7.49 nm3).
In the ferroelectric case, domain switching was studied by generating P-E and butterfly hysteresis loops and by analysing creep-relaxation curves. An insight into the evolution of domain structure and on domain switching mechanisms was gained. Experiments at different frequencies allowed the activation volume to be estimated at the coercive field (77 nm3). The relatively large value indicates small rate dependence and suggests a domain structure with broad and mobile domain walls, being the preferred sites for the nucleation.