Domain Growth in PMN-type Relaxor Ferroelectric Oxides

小行星9703550 已经对PMN弛豫族的成员PMT Pb（Mg 1/3 Ta 2/3）O3进行的初步实验表明，在所有先前尝试中用于促进畴生长的退火温度处于钙钛矿动力学惰性的范围内。 通过采取特殊的预防措施，抑制PbO的挥发，较高的温度热处理表明，域的大小和阳离子有序度可以增加一个数量级以上。 这些观察明确地表明，目前接受的PMN弛豫的“空间电荷”模型是无效的。 在该模型中，在钙钛矿结构的“B-位点”中的金属阳离子的排列中的精细尺度不均匀性被解释为分散在带正电荷的无序基质中的带负电荷的有序纳米域的形成。 这种解释的主要实验支持来自于明显没有任何增长的领域或变化的程度与延长的热处理的有序。 该项目将探索这些结果产生的几种新的研究途径，并重点关注选定的铌酸盐和钽酸盐弛豫体系的结构和性质。 这些研究的目的是：（1）确定PMN型弛豫体的结构状态对不同高温处理的响应;（2）建立与这些观察一致的新的阳离子有序化的晶体化学模型;（3）表征有序度和畴大小的新变量如何影响PMN弛豫体的介电响应;（4）利用这些模型开发新型弛豫陶瓷。 自35年前发现以来，弛豫铁电体在多层电容器、换能器、电光器件和薄膜存储器中的应用引起了广泛的兴趣。 现在众所周知，弛豫系统的介电性质与其晶体结构中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响应物理学的关系的充分理解还不存在。 这对于铅基PMN（铅-镁-铌氧化物）复合钙钛矿弛豫剂尤其如此，这是最知名和最广泛研究的弛豫剂家族，这是本探索性研究的焦点。 对PMN系统进行的广泛研究已经导致了一个模型的建立和接受，作为解释其结构和性质的基础。 主要研究员的初步工作表明，这一模型可能不正确。 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. ***