标题： 偶极向列态在弛豫铁电体中 显示英文标题

标题： Dipolar Nematic State in Relaxor Ferroelectrics

摘要： 弛豫铁电体表现出优异的介电和机电性能，但由于分层极性结构和化学复杂性的相互作用，其微观起源仍然难以捉摸。 虽然基于极性纳米区域或纳米畴的模型提供了有价值的表观见解，但它们通常缺乏必要的第一性原理预测能力，以定量描述压电系数等功能特性。 在这里，我们利用大规模分子动力学模拟，借助一种通用的第一性原理机器学习原子间势能，研究典型铅基、铋基和钡基弛豫铁电体中的原子尺度极性动力学。 在所有系统中，我们发现了一种普遍的偶极向列态，其特征是局部极化的长程取向有序，而没有局部对齐，这挑战了传统的基于极性团簇的范式。 我们引入了一个普遍的序参数，该参数来源于局部极化自相关函数分布的偏度，能够在一个主曲线上捕捉铅基和无铅系统的热演化。 这种向列序及其在电场循环下的强结构记忆，支撑了关键的弛豫铁电现象，包括弥散相变、频率依赖的介电色散和可逆的大压电性。 我们的研究结果建立了一个统一的微观框架来解释弛豫铁电体，并提出了一种广泛适用的统计方法来理解复杂的无序材料。 显示英文摘要

摘要： Relaxor ferroelectrics exhibit exceptional dielectric and electromechanical properties, yet their microscopic origins remain elusive due to the interplay of hierarchical polar structures and chemical complexity. While models based on polar nanoregions or nanodomains offer valuable phenomenological insights, they often lack the first-principles predictive capability necessary for quantitatively describing functional properties such as piezoelectric coefficients. Here, we use large-scale molecular dynamics simulations, enabled by a universal first-principles-based machine-learning interatomic potential, to investigate atomic-scale polar dynamics in canonical Pb-, Bi-, and Ba-based relaxors. Across all systems, we uncover a universal dipolar nematic state, characterized by long-range orientational order of local polarizations without local alignment, challenging conventional polar cluster-based paradigms. We introduce a universal order parameter, derived from the skewness of the distributions of the local polarization autocorrelation functions, that captures the thermal evolution of both lead-based and lead-free systems within a single master curve. This nematic order, and its robust structural memory under electric field cycling, underpins key relaxor phenomena, including diffuse phase transition, frequency-dependent dielectric dispersion, and reversible giant piezoelectricity. Our findings establish a unified microscopic framework for relaxors and present a broadly applicable statistical approach to understanding complex disordered materials.