Development of perovskite-type ceramics and device structures for electrocaloric applications

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This proposal is part of the topical key area dealing with the development of electrocaloric materials for ferroic cooling systems. Specific emphasis is given to the implementation of known and novel electro-ceramic materials into future device structures by using ceramic processes. Two different perovskite-type formulations will be considered: first PMN-PT and secondly BaTiO3. For both compositions, electrocaloric effect has been reported in literature. Modifications of chemical composition in correlation to the specific technology requirements and performance of elements are done as part of own research. In order to limit the operation voltage, reduced thickness of the refrigerant material is necessary. Complimentary to the thin film approach we here consider ceramic powder technologies, which allow for high volume refrigerants. To achieve film thicknesses of 5-50 µm multilayer technology will be applied to build electrocaloric (EC) elements. Influence of multilayer structure (geometrical size, thickness and number of layers; material and thickness of inner electrodes) on dielectric, ferroelectric and electrocaloric properties will be investigated in detail. The development of device structures will be accompanied by a productive and hierarchical structured characterization methodology for measurement of dielectric and ferroelectric properties. Besides, measuring set-up for direct determination of EC effect on large components (< 500 mm2) will be developed. Exchange of test samples and comparison of measurement results contribute to the development of guidelines for reliable measurements and characterization of electrocaloric materials within SPP 1599. The cooling performance of prepared device structures will be systematically characterized aiming at knowledge gain on the correlation between chemical composition, microstructure, device design and operational modes. In view of the development of electrocaloric cooling systems in the consortium, experimental investigations of rate dependent heat release and heat adsorption in dependence of the applied voltage signal will be performed. Results will be compared to simulated data using coupled electrical and thermal analysis. Kinetic approaches are proved to see if they are useful for simplified cooling systems without mechanical switches. Suitable application areas will be identified. In cooperation with project partners of the SPP consortium EC cooling elements in form of ceramic multilayer structures will be integrated into cooling systems. Therefore, we will consider key problems of performance increase and stability under practical operation conditions in experimental studies. Materials, device design and operation modes are tailored to increase cooling efficiency.