The elastocaloric effect in the Bi4Ti3O12(BIT) ferroelectric nanoparticle with vortex domain structure was studied using a phase field simulation in this work. A transformation from the negative elastocaloric effect to positive elastocaloric effect which is associated with vortex domain structure is found under the uniaxial stress in the BIT nanoparticle. In addition, the negative adiabatic temperature change is found under the biaxial compressive stress, and the positive adiabatic temperature change is found under the biaxial tensile stress. The results of this study provide an explanation of the mechanism of the negative/positive elastocaloric effect in the low-dimensional ferroelectrics from the viewpoint of the domain structure.

The effects of grain boundary thickness and grain orientation on the electrical behavior of a ferroelectric field effect transistor with a polycrystalline gate are investigated using a phase field model in conjunction with the basic device equations of the field effect transistor. It is found that the grain boundary and grain orientation have a significant effect on the C-V relation curve and the output characteristic curve through the remnant polarization value and the coercive field of polycrystalline ferroelectric thin film. The grain orientation and grain boundary cause the memory window of the C-V relation curves to narrow. And the grain orientation and grain boundary have an influence on the on/off state source-drain current, decrease their on-off ratio of the output characteristics curves in the ferroelectric field effect transistor.