Understanding pressure-induced depolarization and energy harvesting in ferroelectric and antiferroelectric crystals by fast compression experiments

铁电材料可以在非常短的时间尺度内释放非常大量的存储电能，因为压力诱导的相变在冲击压缩期间产生强烈的脉冲电流。 后者通常由气枪或炸药引起。然而，由冲击波触发的能量释放过程的详细表征在这样的实验中是困难的，因为它们遭受许多问题，如电击穿，漏电流，需要只能使用一次的大样品，以及热加热的影响。在这里，我们建议使用动态金刚石对顶砧单元（dDAC）和激光诱导冲击波的快速压缩研究，以了解在铁电和反铁电材料的能量转换过程中的高功率密度在压力诱导相变。在使用dDAC的实验中，可以达到非常高的压缩率，并且可以重复使用非常小的μ m大小的样本。由于其高导热性，金刚石砧减轻了压缩过程中样品的加热，并使我们能够将压力的影响与温度的影响分开。激光诱导冲击波可以为小μ m或更大尺寸的样品提供高达几GPa的压力，从而补充了dDAC研究。在铁电材料中，压力诱导相变期间的能量释放和电极化的压力依赖行为取决于几个方面，包括相变类型（铁电或反铁电）、相变性质（位移或有序-无序）和相变路径（四方-立方或菱方-立方）。因此，我们打算研究BaTiO 3基和BiFeO 3基铁电体以及Bi 0. 5 Na 0. 5 TiO 3基反铁电体，以便对所有这些方面进行研究。对于样品的表征，我们将使用二次谐波产生（SHG）方法、电学测量、拉曼光谱和X射线衍射。的SHG测量将提供信息的相变和压力引起的极化行为的字符，并进一步允许弛豫铁电体中的纳米畴或极性纳米区域的评估。方法的发展将允许新的SHG测量的偏振在快速压缩dDAC和激光诱导冲击波实验。结合原位二次谐波产生和电荷密度测量，将有助于我们理解快速压缩过程中电极化、电子电导率、击穿场和漏电流之间的相互依赖关系。拉曼光谱和X射线衍射将提供关于局部结构、长程有序和纹理的信息，从而使我们能够理解结构修改和偏振变化之间的相关性。

Ferroelectric materials can release very large amounts of stored electrical energy in a very short time scale as pressure-induced phase transitions generate an intense pulsed current during shock compression. The latter is typically induced by gas guns or explosives. However, a detailed characterisation of the energy release processes triggered by the shock waves is difficult in such experiments, as they suffer from numerous problems such as electric breakdowns, leakage currents, the need for large samples which can only be used once, and the effect of thermal heating. Here, we propose to use dynamic diamond anvil cells (dDAC) and laser-induced shock waves for fast compression studies in order to understand energy conversion processes in ferroelectric and antiferroelectric materials with high power densities during pressure-induced phase transitions. In experiments with dDACs very high compression rates can be reached and very small µm-sized samples can repeatedly be used. Due to their high thermal conductivity, diamond anvils alleviate the heating of the samples during the compression processes and will allow us to separate the influence of pressure from that of temperature. Laser-induced shock waves can provide pressures up to several GPa for small µm-sized or larger samples and thus complement the dDAC studies.This energy release and pressure-dependent behaviour of the electric polarization during pressure-induced phase transitions in ferroelectric materials depends on several aspects, including type of the phase transition (ferroelectric or antiferroelectric), the character of phase transition (displacive or order-disorder) and the transition path (tetragonal-cubic or rhombohedral-cubic). We therefore propose to study BaTiO3- and BiFeO3-based ferroelectrics and Bi0.5Na0.5TiO3- based antiferroelectrics, in order to allow investigations of all these aspects.For the characterisation of samples, we will employ the second harmonic generation (SHG) method, electric measurements, Raman spectroscopy and x-ray diffraction. The SHG measurements will provide information on the character of the phase transitions and the pressure-induced behaviour of polarization and furthermore allow an evaluation of nanodomains or polar nanoregions in relaxor ferroelectrics. Methodological developments will allow novel SHG measurements of the polarization during fast compression in dDAC- and laser-induced shock wave experiments. The combination of in situ second harmonic generation and charge density measurements will help us to understand the interdependence between electric polarization, electronic conductivities, breakdown field and leakage current during the fast compression. Raman spectroscopy and x-ray diffraction will provide information on the local structure, long-range order and texture, and thus allow us to understand the correlation between structural modifications and polarization changes.