Research On Electrocaloric Effect Of Polar Dielectric Materials Under Electric Field

The change of temperature and entropy produced by polar dielectric materials under electric field is called electrocaloric effects(ECE). For decades, polar dielectric materials have only been found to have a relatively small electrothermal effect, which can not be put into practical use. Recently, large electrocaloric effect of ferroelectric materials discovered by researchers arises the interest of study on the refrigeration mechanism which is designed based on the electrocaloric effect of dielectric materials. Compared to the traditional refrigeration technology, refrigerator designed and manufactured using the electrocaloric effect of dielectric materials has the advantages of no pollution and hi gher refrigeration efficiency, thus has a huge application prospect in refrigeration industry.In this paper, based on the Curie- Weiss law, Landau theory of phase transition and the Maxwell equation, the electrocaloric effect equation of polar dielectric materials is deduced, and the changes of temperature and entropy in paraelectric phase and ferroelectric phase(F-P) transition are obtained, meanwhile, comparison of the electrocaloric effect between the two phases are made. These results provide theoretical bases for the maximum temperature change, maximum entropy change and work capacity analysis etc. In addition, thermodynamic models of polar dielectric materials’ electrocaloric effect in paraelectric phase and ferroelectric phase are established. The theory indicates that as long as the working temperature is sufficiently close to the Curie temperature, the electrocaloric effect is relatively large, and larger than that in the paraelectric state. Based on this result, large electrocaloric effect of dielectric materials can be actualized when its Curie temperature is very close to the certain working temperature.The establishment of the typical thermodynamic cycle is the theoretical basis of the study on electrocaloric material’s energy conversion and work capability as refrigeration devices. Therefore, choosing the large polarity dielectric whose Curie temperature is close to room temperature, along with the improvement of design technology, the refrigerator application prospect using polar dielectric’s electrocaloric effect in its paraelectric phase will be greatly guaranteed. In this paper, the potential of large electrocaloric effect of polar dielectric at the temperature below or near its ferroelectric paraelectric phase transition Curie temperature i s verified. This is because the phase transition can lead to the polarity change of dielectric material, and polarity change can cause large entropy change.In the end, the thermodynamic theory of polar elastic dielectric with large thermal effect and large deformation is established. This theory characterizes the equilibrium requirements of polar dielectrics under the coupling of mechanical force, electric field and heat field. The mechanical properties and the large deformation of the dielectric considering the coupling effect of the elastic, polarization, electrostriction and thermal contribution of thermodynamic system are analysed. This study points out the direction of finding the dielectric material with the large electrocaloric effect under certain working temperature(such as room temperature or other special requirements of temperature). Moreover, it also provides a theory guidance for the design and fabrication of refrigerator based on the electrocaloric effect of polar dielectric.