Relaxor ferroelectrics were discovered in the 1950s but many of their properties are not understood. In this review, we shall concentrate on materials such as PMN (PbMg1/3Nb2/3O3), which crystallize in the cubic perovskite structure but with the Mg ion, charge 2+, and the Nb ion, charge 5+, randomly distributed over the B site of the perovskite structure. The peak of the dielectric susceptibility for relaxors is much broader in temperature than that of conventional ferroelectrics, while below the maximum of the susceptibility most relaxors remain cubic and show no electric polarization, unlike that observed for conventional ferroelectrics. Because of the large width of the susceptibility, relaxors are often used as capacitors. Recently, there have been many X-ray and neutron scattering studies of relaxors and the results have enabled a more detailed picture to be obtained. An important conclusion is that relaxors can exist in a random field state, as initially proposed by Westphal, Kleemann and Glinchuk, similar to that which has been studied for diluted antiferromagnets. If a relaxor is cooled from a high temperature, then the Burns temperature is a measure of when slow fluctuations become evident. These fluctuations are connected with the disorder and are known as nano-domains. The Burns temperature is not a well-defined transition temperature. At a lower temperature, there is a well-defined boundary to a so-called random field state when the nano-domains become static but there is no long-range periodic order. This phase may have both history-dependent properties and a skin effect in which the surface of the sample is different from that of the bulk material, as also found in experiments on magnetic systems. Section 1 is an introduction to the review, to ferroelectricity and to relaxors. Section 2 gives a description of the results obtained by dielectric, optical, specific heat and other macroscopic properties. These long-wavelength properties give a variety of different characteristic temperatures and do not directly probe the random field state. In Section 3, we describe the results of neutron and X-ray scattering and show that they strongly support the interpretation that relaxors have a random field state. In Section 4, we briefly describe the results for other relaxor systems such as (PMN)1−x (PT) x for which PMN is mixed with different amounts of the ferroelectric lead titanate (PT), and we show that the existence of a random field state enables us also to describe the experimental results for these mixed materials. We hope that this review will inspire further theoretical and experimental work to understand the nature of the random field states and to compare the experimental results more satisfactorily with theory.

中文翻译：

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用弛豫器放松：弛豫铁电体综述

弛豫铁电体在 1950 年代被发现，但它们的许多特性尚不清楚。在这篇综述中，我们将专注于 PMN (PbMg1/3Nb2/3O3) 等材料，它们在立方钙钛矿结构中结晶，但 Mg 离子，电荷为 2+，Nb 离子，电荷为 5+，随机分布在钙钛矿结构的B位。弛豫的介电磁化率峰值在温度上比传统铁电体的要宽得多，而在磁化率最大值以下，大多数弛豫保持立方并且没有电极化，这与传统铁电体观察到的不同。由于磁化率的宽度很大，因此通常使用弛豫器作为电容器。最近，已有许多关于弛豫的 X 射线和中子散射研究，其结果能够获得更详细的图片。一个重要的结论是弛豫可以以随机场态存在，正如 Westphal、Kleemann 和 Glinchuk 最初提出的那样，类似于稀释反铁磁体的研究。如果弛豫器从高温冷却，那么伯恩斯温度是衡量缓慢波动何时变得明显的指标。这些波动与无序有关，被称为纳米域。伯恩斯温度不是一个明确定义的转变温度。在较低温度下，当纳米域变为静态但没有长程周期顺序时，所谓的随机场状态存在明确的边界。该相可能具有历史相关特性和集肤效应，其中样品的表面与散装材料的表面不同，这在磁系统实验中也发现。第 1 节是对综述、铁电性和弛豫剂的介绍。第 2 节描述了通过介电、光学、比热和其他宏观特性获得的结果。这些长波长特性给出了各种不同的特征温度，并且不直接探测随机场状态。在第 3 节中，我们描述了中子和 X 射线散射的结果，并表明它们强烈支持弛豫具有随机场状态的解释。在第 4 节中，我们简要描述了其他弛豫系统的结果，例如 (PMN)1-x (PT) x，其中 PMN 与不同量的铁电钛酸铅 (PT) 混合，我们表明随机场状态的存在使我们还描述了这些混合材料的实验结果。我们希望这篇综述能激发进一步的理论和实验工作，以了解随机场态的性质，并将实验结果与理论进行更令人满意的比较。