弛豫体PMN中的极性振动激发与类玻璃响应
Polar vibrational excitations and glass-like response in relaxor PMN
- Princeton University（普林斯顿大学）
- Lawrence Berkeley National Laboratory（劳伦斯伯克利国家实验室）
机构由 AI 辅助整理，请以论文原文为准。
AI总结：
本研究通过第一性原理训练的原子模型，揭示了弛豫铁电体PMN中无序诱导的极性振动激发谱，解释了其介电、光学和热异常，并关联了类玻璃响应。
AI中文摘要：
弛豫铁电体在保持晶体有序性的同时，展现出类玻璃的介电和热响应。利用基于第一性原理数据训练的原子级模型，我们研究了典型弛豫体Pb(Mg_{1/3}Nb_{2/3})O_3 (PMN)中的这些响应。成分无序将弹性运动与电极化耦合，产生连续的极性振动激发谱，这与传统铁电体PbTiO_3中离散的极性光学模式不同。模拟定性地再现了低频磁化率的温度依赖性，而计算得到的远红外光谱与实验密切吻合。在低频下，PMN中的无序产生了一个玻色峰，包含过剩的类声子模式和准局域激发。后者表现出其态密度的四次方频率依赖性以及显著的非谐性，如同结构玻璃中的情形。这些过剩模式解释了PMN在温度高于5 K时比热中的反常行为。这些结果通过无序诱导的极性激发谱，将晶体弛豫体的介电、光学和热异常联系起来。
英文摘要：
Relaxor ferroelectrics retain crystalline order while exhibiting glass-like dielectric and thermal responses. Using atomistic models trained on first-principles data, we investigate these responses in the prototypical relaxor Pb(Mg_{1/3}Nb_{2/3})O_3 (PMN). Compositional disorder couples elastic motion to electric polarization, producing a continuum of polar vibrational excitations, unlike the discrete polar optical modes of conventional ferroelectric PbTiO_3. The simulations qualitatively reproduce the temperature dependence of the low-frequency susceptibility, while the calculated far-infrared spectra agree closely with experiments. At low frequencies, disorder in PMN generates a boson peak comprising excess phonon-like modes and quasi-localized excitations. The latter exhibit a quartic frequency dependence of their density of states and pronounced anharmonicity, as in structural glasses. These excess modes account for PMN's anomalous behavior in the specific heat for temperature higher than 5 K. These results connect the dielectric, optical, and thermal anomalies of a crystalline relaxor through its disorder-induced polar excitation spectrum.
