High-temperature polar clusters in perovskite-type relaxor ferroelectrics and their response to an electric field

弛豫铁电体是一种局部非均匀材料，由于其特殊的介电、机电和电光响应而引起了人们的极大关注。这种独特的弛豫性能与分散在整个立方结构中的极性纳米团簇的存在有关。对于凝聚态物理学家和材料科学家来说，理解实际的极性原子团簇及其与弛豫性质的相互作用是一个巨大的挑战。这个项目的目的是分析在高于介电常数最大温度的温度下，形成极性纳米区域的优先极性原子移动和耦合过程。为此，我们将利用共振拉曼光谱技术在670-80K的温度范围内对模型化合物(化学计量比和掺Ba的PbSc0.5Ta0.503和PbSc0.5Nb0.503)进行分析，以分析通过增强的纵向光学模式的变化来分析极性物种的平均尺寸和分布的演变。此外，还将在850-80K的外电场作用下，用原位常规拉曼光谱对同一化合物进行研究，以阐明相干极性原子位移的择优结晶方向和极性团簇的可切换性。此外，还将用拉曼光谱和椭圆偏振光谱仪分析新合成的含Ru的PbSc0.5Ta0.5O3、PbSc0.5Nb0.503和0.9PbZn1/3Nb2/3O3-PbTiO3的声子态和价电子态的温度演化。

Relaxor ferroelectrics are locally inhomogeneous materials that have been attracted tremendous attention due to their exceptional dielectric, electromechanical and electrooptic response. The unique relaxor properties are related to the existence of polar nanoclusters dispersed in the overall cubic structure. The understanding of the actual polar atomic clustering and its interplay with the relaxor properties is a great challenge to condensed-matter physicists and materials scientists. This project aims to analyze the preferential polar atomic shifts and coupling processes to form polar nanoregions at temperatures above the temperature of the dielectric permittivity maximum. For the purpose, resonance Raman spectroscopy will be applied to model compounds (stoichiometric and Ba-doped PbSc0.5Ta0.5O3 and PbSc0.5Nb0.5O3) in the temperature range 670 – 80 K to analyze the evolution of the mean size and distribution of polar species via the changes in the enhanced longitudinal optical modes. Further, the same compounds will be studied by in situ conventional Raman spectroscopy under an external electric field at temperatures between 850 and 80 K to elucidate the preferred crystallographic direction of coherent polar atomic displacements and the switchability of polar clusters. In addition, the temperature evolution of phonon and valence-electron states of newly synthesized Ru-containing PbSc0.5Ta0.5O3, PbSc0.5Nb0.5O3 and 0.9PbZn1/3Nb2/3O3-PbTiO3 will be analyzed by Raman spectroscopy and optical ellipsometry.