Design of electrocaloric multilayer refrigerators via multi-scale modeling

通过将提供显着电热容量的弛豫铁电体与由具有可调导热系数的铁电材料组成的热开关相结合，可以构建不需要固体或流体部件运动的冷却装置。本项目旨在对这种代表低电压微冷却系统的多层固态冷却装置进行概念设计和优化。连续尺度和原子模拟都计划用于支持材料设计和优化多层堆的冷却性能。在连续体水平上，对电冰箱内的瞬态热传导进行有限元建模研究。有限元模拟的新颖之处包括基于畴结构的EC热产生/吸收计算，考虑具有可调电导率的热交换层，以及基于原子模拟的界面传导模型。此外，有限元建模易于与静力学和力学相结合。在概念设计和数值优化中，几何参数如层厚度和电极配置将被研究。在原子尺度上计算特征材料参数。我们将探索ECE与\NBT \和\BST \弛豫行为之间的关系，并继续开发允许定量预测的模型哈密顿量。目标是建立具有不同复杂程度和效率的模型系统（ising型、landau型和基于ab-initio的），以系统地研究影响电热材料ECE的关键因素。一个新的方面将是模拟电热材料和热敏开关之间的界面。

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.