In the PhD research, phase field simulations were conducted to study the polarization behavior and properties of ferroelectric materials. Four aspects of ferroelectric materials were simulated, which are 1) electrocaloric effect, 2) the influence of dislocation walls, 3) fracture; and 4) the influence of {111} twins.

Electrocaloric effect of ferroelectric materials, which occurs significantly near the first-order paraelectric/ferroelectric transition (FOPFT) Curie temperature, has great potential in solid-state refrigeration. Most ferroelectric materials, however, bear the second-order paraelectric/ferroelectric transition. The simulations find two types of pseudo-first-order phase transition (PFOPT) and two types of electric-field-induced-pseudo-phase transition (EFIPPT), asso...[ Read more ]

In the PhD research, phase field simulations were conducted to study the polarization behavior and properties of ferroelectric materials. Four aspects of ferroelectric materials were simulated, which are 1) electrocaloric effect, 2) the influence of dislocation walls, 3) fracture; and 4) the influence of {111} twins.

Electrocaloric effect of ferroelectric materials, which occurs significantly near the first-order paraelectric/ferroelectric transition (FOPFT) Curie temperature, has great potential in solid-state refrigeration. Most ferroelectric materials, however, bear the second-order paraelectric/ferroelectric transition. The simulations find two types of pseudo-first-order phase transition (PFOPT) and two types of electric-field-induced-pseudo-phase transition (EFIPPT), associated with ultrahigh electrocaloric effect in ferroelectric nanoparticles, which compensate the scarcity of FOPFT. The PFOPT and EFIPPT should be general, applicable to all ferroelectric perovskite materials.

The influences of dislocation walls on the micro-structure signature and the macro-response of a ferroelectric single crystal were simulated in terms of the dislocation linear density, applied electric field amplitude, bias field, temperature and frequency. The micro-domain configuration and polarization switching are greatly changed for the existence of dislocation arrays, and correspondingly the macro-response is significantly influenced, which can explain many controversial or abnormal observations in experiments.

A novel surface energy potential was proposed to study the fracture behavior of single crystal ferroelectric materials. When the surface energy potential is added into the existing energetic phase field approach, one can simulate brittle fracture and polarization simultaneously.

The role of {111} lattice twins in the polarization switching of both single grain and polycrystalline ferroelectric materials was also simulated to explain and compare with the relevant experimental results by SG Cao. The simulation results show that {111} lattice twins can effectively reduce the coercive field while reserving the remnant polarization.

The new findings from the phase field simulations enhance the understanding of ferroelectric materials and provide novel physical perspectives for experiments.