Dynamics and microscopic origin of the electrocaloric effect in relaxor ferroelectrics

我们将研究弛豫铁电体中电热效应的复杂动力学行为。通过探测热辐射对绝热温度变化Delta T的直接非接触测量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。结构和对称性的变化将通过激光脉冲的光学二次谐波产生来灵敏地探测，这允许极快地监测例如，在电场循环期间材料中的极区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松弛材料中所谓的极性纳米区域的快速动力学提供新的见解，这些纳米区域被认为是这些材料中巨大的电热效应的原因。此外，还将调查松弛剂中发现的缓慢衰老和返老还童的行为，旨在为如何抑制松弛材料中的衰老提供指导。我们将把测量带宽扩展到超过1 MHz，这将使我们能够快速地将热扩散到衬底，并系统地研究新的电热材料(在其开发的早期阶段)，这些材料只能以层或薄膜的形式提供。

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.