| Refrigeration technology has a very wide range of applications in today’s human activities. For more than one hundred years, the vapor compression technology as the main refrigeration technology has played a huge role in promoting the development of human civilization. But because of the compressor working such as friction, leakage, harmful heat transfer etc. factors, actual work efficiency of a compressor is difficult to achieve 50% of Carnot cycle efficiency, and the gases. Freon or CFCs used as compressor refrigerant which are easy to leak to destruct the ozone layer. Weakening of the ozone layer of UV filtering effect will not only cause global greenhouse effect, will increase the incidence of skin cancer in humans and threaten to human public health. With the energy and environmental problems become more and more important, the vapor compression technology is facing severe challenges. It is urgent to explore an efficient and environmentally friendly refrigeration technology. This paper is to investigate the electrocaloric effect of ferroelectric materials, which is expected to replace the vapor compression refrigeration, by selecting the ferroelectric materials in typical lanthanum doped lead zirconate titanate(PLZT) ceramic thickfilms.The electrocaloric effect is the adiabatic temperature change and the isothermal entropy change in the polar dielectric material due to the change of the electric field induced by the change of the polarization state. In the doped PZT ceramics, lanthanum substituted lead was obtained, which has excellent dielectric, piezoelectric, pyroelectric and electro-optic properties, conductivity and phase transition temperature can be changed by varying the composition or adding impurities to be adjusted, and is an ideal electrocaloric material. The preparation technology of thick film ferroelectric electrocaloric device can withstand larger electric field, not to be broken down. Inaddition, thick film devices work at low voltages and frequencies of a wide range of advantages, and can be compatible with semiconductor integrated circuit technology, and it is expected to have excellent electrocaloric effect.In this paper, PbO, La2O3, ZrO2 and TiO2 oxides were used for high temperature solid-phase synthesis of PLZT powder. Then the PLZT powders were made of green tape by tape-casting, and further sintered under suitable conditions. In the meantime, we design a method to remove the bubbles in the PLZT slurry before tape-casting. For the thick film ceramics obtained, by X-ray diffraction (XRD), scanning electron microscopy (SEM) and other characterization techniques were used to characterize the sample phase composition, ceramic density and grain size and grain boundary structure etc. The dielectric and ferroelectric properties were tested by the precision Impedance analyzer and Sawyer-Tower circuit. Results show that the thick film ceramics have good electrocaloric effect at room temperature (at 293K, △S=1.08J/(kg-K), AT=0.96K). In addition, the relaxor ferroelectric PLZT 11/70/30 and anti-ferroelectric PLZT7/82/18 ferroelectric thick films were also fabricated and their electrocaloric effects were measured. The results show that PLZT11/70/30 has a △T=2.21K at 423K and PLZT7/82/18 has a △T=1.04K at 414K. The electrocaloric efficiency △T/△E for these two compositions were calculated and found there are 0.32 and 0.30 respectively, which are larger than those reported recently. The larger electrocaloric efficiencies obtained may be clue to the synergic electrocaloric effect occurred in relaxor ferroelectric phase and anti-ferroelectric phase. The mechanism is further studying now. |
