Domain Growth in PMN-type Relaxor Ferroelectric Oxides

对pmn -弛豫家族成员PMT Pb(Mg1/3Ta2/3)03进行的初步实验表明，在之前所有促进畴生长的尝试中使用的退火温度都在钙钛矿的动力学惰性范围内。通过采取特殊的预防措施来抑制PbO的挥发，高温热处理表明，结构域的大小和阳离子有序度可以增加一个数量级以上。这些观察结果明确地表明，目前公认的PMN弛豫量的“空间电荷”模型是无效的。在这个模型中，钙钛矿结构中b位金属阳离子排列的精细尺度不均匀性被解释为在带正电的无序基质中分散形成带负电的有序纳米畴。这种解释的主要实验支持来自于延长热处理后明显没有任何域的生长或有序程度的变化。该项目将探索从这些结果中产生的几个新的研究途径，并将重点放在选定的铌酸盐和钽酸盐弛豫系统的结构和性质上。这些研究的目的是：(1)建立pmn型弛豫剂的结构状态对不同高温处理的响应；(2)建立与这些观测结果相一致的新的阳离子有序晶体化学模型；(3)表征有序度和畴尺寸这一新变量对PMN弛豫器和的介电响应的影响；(4)利用这些模型开发新型弛豫陶瓷。自从35年前发现弛豫铁电体以来，它在多层电容器、换能器、电光器件和薄膜存储器等领域的应用引起了广泛的兴趣。现在大家都知道弛豫系统的介电性质与其晶体结构的局域无序密切相关。然而，对结构不均匀性的起源及其与弛豫反应的物理关系的充分理解尚不存在。对于铅基PMN（铅-镁-氧化铌）复合钙钛矿弛缓剂尤其如此，这是最知名和广泛研究的弛缓剂家族，也是本探索性研究的重点。对PMN系统进行的广泛研究已经导致建立和接受一种模型，作为解释其结构和特性的基础。首席研究员的初步工作表明，这个模型可能不正确。该项目将进行实验，以确认PI的模型，然后将用于开发新的弛豫材料。＊＊＊

9703550 Davies Preliminary experiments that have been conducted on a member of the PMN-relaxor family, PMT Pb(Mg1/3Ta2/3)03 indicate that the annealing temperatures utilized in all the previous attempts to promote domain growth lie in a range where the perovskite is kinetically inert. By taking special precautions that inhibit the volatilization of PbO, higher temperature heat treatments reveal that the size of the domains and degree of cation ordering can be increased by more than an order of magnitude. These observations unambiguously show that the currently accepted "space charge" models for the PMN relaxors are invalid. In this model the fine-scale inhomogeneities in the arrangements of the metal cations in the "B-sites" of the perovskite structure are interpreted in terms of the formation of negatively charged ordered nano-domains dispersed in a positively charged disordered matrix. The primary experimental support for this interpretation comes from the apparent absence of any growth of the domains or change in the degree of ordering with extended thermal treatment. This project will explore several new avenues of research that emanate from these results and focuses on the structure and properties of selected niobate and tantalate relaxor systems. The goals of these studies are: (1) to establish how the structural state of PMN-type relaxors respond to different high temperature treatments; (2) to develop new crystal chemical models for the cation ordering that are consistent with these observations; (3) to characterize how the new variable of degree of order and domain size affects the dielectric response of the PMN relaxers and; (4) to exploit these models to develop new relaxor ceramics. %%% Since their discovery over 35 years ago, relaxor ferroelectrics have attracted widespread interest for applications in multi-layer capacitors, transducers, electro-optic devices, and thin film memories. It is now well known that the dielectric properties of relaxor systems are intimately linked to the localized disorder in their crystal structures. However, a full understanding of the origins of the structural inhomogeneities and their relationship to the physics of the relaxor response does not yet exist. This is particularly true for the lead-based PMN (lead-magnesium-niobium oxide) complex perovskite relaxors, the most well known and widely studied family of relaxors, which are the focus of this exploratory study. The extensive studies that have been conducted on the PMN systems have led to the establishment and acceptance of one model as a basis for explaining their structures and properties. Preliminary work by the Principal Investigator has shown that this model may not be correct. The project will perform experiments to confirm the PI's model that will then be used to develop new relaxor materials. ***