Kim Jieun, Takenaka Hiroyuki, Qi Yubo, Damodaran Anoop R, Fernandez Abel, Gao Ran, McCarter Margaret R, Saremi Sahar, Chung Linh, Rappe Andrew M, Martin Lane W
Department of Materials Science and Engineering, University of California, Berkeley, Berkeley, CA, 94720, USA.
Department of Physics, University of Nebraska, Lincoln, Lincoln, NE, 68588, USA.
Adv Mater. 2019 May;31(21):e1901060. doi: 10.1002/adma.201901060. Epub 2019 Apr 10.
Understanding and ultimately controlling the large electromechanical effects in relaxor ferroelectrics requires intimate knowledge of how the local-polar order evolves under applied stimuli. Here, the biaxial-strain-induced evolution of and correlations between polar structures and properties in epitaxial films of the prototypical relaxor ferroelectric 0.68PbMg Nb O -0.32PbTiO are investigated. X-ray diffuse-scattering studies reveal an evolution from a butterfly- to disc-shaped pattern and an increase in the correlation-length from ≈8 to ≈25 nm with increasing compressive strain. Molecular-dynamics simulations reveal the origin of the changes in the diffuse-scattering patterns and that strain induces polarization rotation and the merging of the polar order. As the magnitude of the strain is increased, relaxor behavior is gradually suppressed but is not fully quenched. Analysis of the dynamic evolution of dipole alignment in the simulations reveals that, while, for most unit-cell chemistries and configurations, strain drives a tendency toward more ferroelectric-like order, there are certain unit cells that become more disordered under strain, resulting in stronger competition between ordered and disordered regions and enhanced overall susceptibilities. Ultimately, this implies that deterministic creation of specific local chemical configurations could be an effective way to enhance relaxor performance.
理解并最终控制弛豫铁电体中的大机电效应，需要深入了解局域极性有序在施加刺激下是如何演变的。在此，对典型弛豫铁电体0.68PbMgNbO - 0.32PbTiO外延膜中双轴应变诱导的极性结构演变以及极性结构与性能之间的相关性进行了研究。X射线漫散射研究表明，随着压缩应变的增加，漫散射图案从蝶形演变为盘形，相关长度从约8纳米增加到约25纳米。分子动力学模拟揭示了漫散射图案变化的起源，以及应变诱导极化旋转和极性有序的合并。随着应变幅度的增加，弛豫行为逐渐受到抑制，但并未完全消除。对模拟中偶极排列动态演变的分析表明，虽然对于大多数晶胞化学组成和构型而言，应变促使其趋向于更类似铁电体的有序状态，但存在某些晶胞在应变下变得更加无序，导致有序区域和无序区域之间的竞争加剧，整体磁化率增强。最终，这意味着确定性地创建特定的局部化学构型可能是提高弛豫性能的有效方法。
