Abstract
Both relaxor ferroelectric and antiferroelectric materials can individually demonstrate large electrocaloric effects (ECE). However, in order to further enhance the ECE it is crucial to find a material system, which can exhibit simultaneously both relaxor ferroelectric and antiferroelectric properties, or easily convert from one into another in terms of the compositional tailoring. Here we report on a system, in which the structure can readily change from antiferroelectric into relaxor ferroelectric and vice versa. To this end relaxor ferroelectric Pb0.89La0.11(Zr0.7Ti0.3)0.9725O3 and antiferroelectric Pb0.93La0.07(Zr0.82Ti0.18)0.9825O3 ceramics were designed near the antiferroelectric-ferroelectric phase boundary line in the La2O3-PbZrO3-PbTiO3 phase diagram. Conventional solid state reaction processing was used to prepare the two compositions. The ECE properties were deduced from Maxwell relations and Landau-Ginzburg-Devonshire (LGD) phenomenological theory, respectively, and also directly controlled by a computer and measured by thermometry. Large electrocaloric efficiencies were obtained and comparable with the results calculated via the phenomenological theory. Results show great potential in achieving large cooling power as refrigerants.
Highlights
Cooling technologies have been widely used in industry, agriculture and human daily life
When the external electric field is removed, the entropy of the electric dipoles increases due to the transition from an ordered to a disordered state, the temperature of the electrocaloric effect (ECE) material will be reduced under adiabatic conditions[4,5,7]
It was suggested that the addition of La3+ ions produces a significant number of lattice vacancies and results in the enhancement of the densification in the PLZT ceramics[13]
Summary
Cooling technologies have been widely used in industry, agriculture and human daily life. When an electric field is applied to the electrocaloric material, the electric dipoles become ordered from a disordered state, which leads to the reduction of entropy associated with the polarization. When the external electric field is removed, the entropy of the electric dipoles increases due to the transition from an ordered to a disordered state, the temperature of the ECE material will be reduced under adiabatic conditions[4,5,7]. An antiferroelectric to ferroelectric phase transition will be induced when a large enough electric field is applied. During this process, the reorientation of the two opposite dipoles in a unit cell may lead to a large entropy change. The predictions deduced from Maxwell relation and phenomenological LGD theory are compared to the results obtained by the direct measurements
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