Electrocaloric effect in lead-free relaxor ceramics and composites

无铅弛豫陶瓷和复合材料中的电热效应

• 批准号: 226912369
• 负责人: Professor Dr. Doru Constantin Lupascu
• 金额: --
• 依托单位: Institut für Materialwissenschaft
• 依托单位国家: 德国
• 项目类别: Priority Programmes
• 财政年份: 2012
• 资助国家: 德国
• 起止时间: 2011-12-31 至 2017-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/226912369?language=en
• 关键词: Electrocaloric; effect; lead; free; relaxor

This proposal is focused on the search for bulk lead free materials exhibiting maximum electrocaloric effect in the vicinity of room temperature and their characterization. During the course of the first project phase, we have built two set-ups for the direct measurements of the electrocaloric effect. One is an isothermal set-up based on a differential scanning calorimeter the other one is a custom built adiabatic set-up. Both set-ups have been tuned for reliable reproducible results. We found that there is a large difference between the typically indirectly calculated cooling power of electrocaloric systems and their real heat changing properties. 50% difference is typical in relaxors. In the second project phase, we intend to systematically study the electrocaloric effect in lead free relaxor ferroelectrics. The relaxor state offers additional degrees of freedom contributing to entropy change under applied electric fields. The big advantage of relaxors is the broad temperature range of similar cooling capacity. This provides larger refrigerant capacity in comparison to classical ferroelectric systems. We have chosen systems where, additionally to the relaxor state, the phase transitions occur in the vicinity of room temperature. This is a highly valuable property when looking at electrocaloric application.Not only the effect of composition, but also the influence of the microstructure on the electrocaloric effect will be addressed, namely: crystallographic orientation, grain size, and density of ceramics.Large electric fields must be applied for maximum cooling. In order to be able to do so, the ceramics must show very high breakdown resistance. We are seeking this property by high densification. A second approach uses composites. We have developed a chemical route to generate hydrophobic nano- and micropowders of BaTiO3 and its vicinal relaxor systems. These are incorporated into the ferroelectric polymer system PVDF-TrFE which itself is a good electrocaloric material. Both materials, filler and matrix, offer close Curie points. Our hope is that this will permit to construct materials of even higher cooling power at or near room temperature. The big advantage is the large breakdown strength of the polymer which we hope to be able to transfer to the composite. The results will be compared with theoretical models developed by other groups of the Priority Program.We consider our role within the Schwerpunktrpogramm as a central measurement project for the electrocaloric characterization of bulk materials. Having seen the quality of work that is necessary to built reliable set-ups, we consider this our most important contribution to the overall Schwerpunkt. Furthermore, we offer thermal transport, electrical, and structural characterization. Particularly piezoforce microscopy is one of our strengths. We furthermore offer our best materials to the near device projects of the Schwerpunktprogramm.

该提案的重点是寻找在室温附近表现出最大电热效应的块状无铅材料及其表征。在第一个项目阶段的过程中，我们建立了两个用于直接测量电热效应的装置。一种是基于差示扫描量热计的等温装置，另一种是定制的绝热装置。两种设置均已针对可靠的可重复结果进行了调整。我们发现，通常间接计算的电热系统的冷却功率与其实际的热变化特性之间存在很大差异。 50% 的差异在松弛剂中是典型的。在项目第二阶段，我们打算系统地研究无铅弛豫铁电体的电热效应。弛豫态提供了额外的自由度，有助于在施加的电场下熵变。弛豫器的一大优点是相似冷却能力的宽温度范围。与传统的铁电系统相比，这提供了更大的制冷剂容量。我们选择的系统，除了弛豫态之外，相变还发生在室温附近。在考虑电热应用时，这是一个非常有价值的特性。不仅会讨论成分的影响，还会讨论微观结构对电热效应的影响，即：陶瓷的晶体取向、晶粒尺寸和密度。大电场必须采用最大程度的冷却。为了能够做到这一点，陶瓷必须具有非常高的击穿电阻。我们正在通过高密度化来寻求这种特性。第二种方法使用复合材料。我们开发了一种化学途径来生成 BaTiO3 及其邻位弛豫系统的疏水性纳米和微米粉末。这些被纳入铁电聚合物系统 PVDF-TrFE 中，该系统本身就是一种良好的电热材料。填料和基体这两种材料都具有接近的居里点。我们希望这将允许构建在室温或接近室温下具有更高冷却能力的材料。最大的优点是聚合物的高击穿强度，我们希望能够将其转移到复合材料中。结果将与优先计​​划其他小组开发的理论模型进行比较。我们认为我们在 Schwerpunktrpogramm 中的角色是散装材料电热表征的中心测量项目。在了解了建立可靠设置所需的工作质量后，我们认为这是我们对整个 Schwerpunkt 的最重要贡献。此外，我们还提供热传输、电学和结构表征。特别是压力显微镜是我们的优势之一。我们还为 Schwerpunktprogramm 的近设备项目提供最好的材料。