| dc.description.abstract | A comprehensive study of domain switching process in different ferroelastic and
ferroelastic/ferroelectric perovskite structured ceramics has been performed. The
effects of thermal fluctuations on domain switching dynamics were investigated in the
ferroelastic and in the ferroelectric case under static and dynamic electric and
mechanical conditions.
In the ferroelastic case, domain switching behaviour was investigated for different
compositions, using different types of mechanical tests. Compression tests were
carried out to characterize 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 characterized 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, providing original sets of data. 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 2.44 nm3, 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. In creep
experiments, the polarization and the strain were measured simultaneously, during the
application of a constant electric field. An insight into the evolution of domain
structure and on domain switching mechanisms was gained, highlighting analogies
and differences with the ferroelastic case. 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. | en_US |
