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离效应及其表征的批量无铅材料。在第一个项目阶段的过程中，我们建立了两个设置，用于直接测量电源效应。一个是基于差分扫描热量表的等温设置，另一个是定制的绝热设置。两种设置均已调整为可靠的可重复性结果。我们发现，电源系统的通常间接计算出的冷却能力与它们实际变化的特性之间存在很大差异。休闲剂中典型的差异为50％。在第二个项目阶段，我们打算系统地研究铅游离弛豫铁电气中的电脑效应。放松状态提供额外的自由度，在应用电场下导致熵变化。放松剂的最大优势是相似冷却能力的广泛温度范围。与经典的铁电系统相比，这提供了更大的制冷剂能力。我们选择了系统，除了放松状态，相位过渡发生在室温附近。当查看电源应用时，这是一种高度有价值的特性。不仅可以解决组成的效果，而且还可以解决微观结构对电局效应的影响，即：晶体学方向，晶粒尺寸和陶瓷密度必须应用于最大的冷却。为了能够做到这一点，陶瓷必须表现出很高的抗崩溃阻力。我们正在通过高致密化来寻求此属性。第二种方法使用复合材料。我们已经开发了一种化学途径，以产生Batio3及其替代宽松系统的疏水纳米和微源。这些被整合到铁电聚合物系统PVDF-TRFE中，该系统本身是一种很好的电代码材料。材料（填充物和矩阵）都提供了近距离点。我们的希望是，这将允许在室温或接近室温下构造更高冷却能力的材料。最大的优势是聚合物的巨大分解强度，我们希望能够转移到复合材料中。结果将与优先计​​划的其他组开发的理论模型进行比较。我们将我们在Schwerpunktrpogramm中的作用视为散装材料电流表征的中心测量项目。在看到建立可靠的设置所需的工作质量之后，我们认为这对整个Schwerpunkt做出了最重要的贡献。此外，我们提供热传输，电气和结构表征。特别是压电显微镜是我们的优势之一。此外，我们为Schwerpunktprogramm的近设备项目提供了最好的材料。