Dynamics and microscopic origin of the electrocaloric effect in relaxor ferroelectrics

我们将研究弛豫铁电体中热电效应的复杂动力学行为。通过检测热辐射直接非接触测量绝热温度变化δ T将与低于毫秒的时间分辨结构数据和时间分辨极化数据P(E)相关联。结构和对称的变化将由激光脉冲产生的光学二次谐波灵敏地探测，这允许极快地监测，例如，在电场循环期间材料中极性区域的变化和热平衡中的结构波动。这三种方法的独特结合将为弛豫材料中所谓的极性纳米区域的快速动力学提供新的见解，弛豫材料被认为是这些材料中巨大的电热效应的原因。此外，将研究松弛剂中发现的延缓衰老和恢复青春的行为，旨在为松弛剂材料如何抑制衰老提供指导。我们将把测量带宽扩展到1mhz以上，这将使我们能够快速地将热扩散到衬底中，并系统地研究（在开发的早期阶段）只能以层或薄膜形式提供的新电热材料。

We will study the complex dynamic behavior of the electrocaloric effect in relaxor ferroelectrics. Direct contactless measurements of the adiabatic temperature change Delta T via detection of thermal radiation will be correlated with below millisecond time-resolved structural data and time-resolved polarization data P(E). The structural and symmetry changes will be sensitively probed by optical second harmonic generation from laser pulses which allows for an extremely fast monitoring of, e.g., the change of polar regions in a material during electric field cycling and of structural fluctuations in thermal equilibrium. The unique combination of all three methods will give new insights into the fast dynamics of the so-called polar nano-regions in relaxor materials that are thought to be responsible for the huge electrocaloric effect in theses materials. Moreover, the slow aging and rejuvenation behavior found in relaxors will be investigated, aiming for guidelines for how to suppress aging in relaxor materials. We will extend the measurement bandwidth to beyond 1 MHz, which will allow us to beat fast heat diffusion into the substrate and to systematically investigate also new electrocaloric materials that (in their early stage of development) are only available as layers or thin-films.