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。通过检测热辐射对绝热温度变化Δ T的直接非接触测量将与毫秒以下的时间分辨结构数据和时间分辨偏振数据P（E）相关。结构和对称性变化将通过激光脉冲的光学二次谐波产生灵敏地探测，这允许非常快速地监测，例如，电场循环过程中材料极性区域的变化和热平衡中结构波动的变化。所有三种方法的独特组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，这些区域被认为是这些材料中巨大电热效应的原因。此外，还将研究弛豫材料中发现的缓慢老化和再生行为，旨在为如何抑制弛豫材料的老化提供指导。我们将把测量带宽扩展到1 MHz以上，这将使我们能够击败快速热扩散到衬底中，并系统地研究新的电热材料，这些材料（在其开发的早期阶段）只能作为层或薄膜使用。

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.