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首页> 外文期刊>Physical review >Paraelectric and ferroelectric states in a model for relaxor ferroelectrics
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Paraelectric and ferroelectric states in a model for relaxor ferroelectrics

机译：弛豫铁电体模型中的顺电和铁电态

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摘要

We study the free-energy landscape of a minimal model for relaxor ferroelectrics. Using a variational method which includes leading correlations beyond the mean-field approximation as well as disorder averaging at the level of a simple replica theory, we find metastable paraelectric states with a stability region that extends to zero temperature. The free energy of such states exhibits an essential singularity for weak compositional disorder pointing to their necessary occurrence. Ferroelectric states appear as local minima in the free energy at high temperatures and become stable below a coexistence temperature T_c. We calculate the phase diagram in the electric-field-temperature plane and find a coexistence line of the polar and nonpolar phases which ends at a critical point. First-order phase transitions are induced for fields sufficiently large to cross the region of stability of the metastable paraelectric phase. These polar and nonpolar states have distinct structure factors from those of conventional ferroelectrics. We use this theoretical framework to compare and gain physical understanding of various experimental results in typical relaxors.
机译：我们研究松弛铁电最小模型的自由能态。使用一种变分方法，该方法包括超越平均场近似的领先相关性以及简单复制理论水平的无​​序平均，我们发现了亚稳顺电态，其稳定区延伸至零温度。这种状态的自由能对于弱的组成紊乱表现出必不可少的奇异性，指出它们必然发生。铁电态在高温下表现为自由能中的局部最小值，并在共存温度T_c以下变得稳定。我们计算了电场-温度平面中的相图，并找到了在临界点处终止的极性相和非极性相的共存线。对于足够大以穿过亚稳态顺电相的稳定区域的场，感应出一阶相变。这些极性和非极性状态具有与常规铁电体不同的结构因素。我们使用此理论框架来比较并获得对典型松弛器中各种实验结果的物理理解。

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