Design of electrocaloric multilayer refrigerators via multi-scale modeling

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By combining relaxor ferroelectrics that provide a significant electrocaloric capacitywith thermal switches consisting of ferroelectric materials with tunable thermal conductivity cooling devices can be build, which do not require the motion of solid or fluid parts. This project aims at the conceptual design and optimization of such multilayer solid-state cooling units that represent micro-cooling systems operating at low voltage.Both, continuum scale and atomistic simulations are planned to support the materials design and to optimize the cooling performance of the multilayer stacks. On the continuum level, finite element modeling will be carried out to study the transient heat conduction in refrigerators. Novelties of the FE simulations include domain-structure-based calculation of the EC heat generation/absorption, consideration of thermal switch layer with tunable conductivity, and atomistic-simulation-based interface conduction model. Besides, the FE modeling is readily to be coupled with electrostatics and mechanics. In the conceptual design and numerical optimizations geometric parameters such as layers thickness and electrode configurations will be investigated. On the atomic scale characteristic materials parameters will be calculated. We will explore the relation between the ECE and the relaxor behaviorof \NBT \, and \BST \, and continue with the development of model Hamiltonians that allow for quantitativepredicitions. The goal is to have model systems with different levels of sophistication and efficiency (Ising-type, Landau-type andab-initio based) available to systematically study the key factors affecting the ECE in electrocaloric materials. A new aspect will be the modelling of interfaces between the electrocaloric material and the thermal switches.