Chemical and Thermal Modification of PMN-Type Relaxor Ferroelectrics

35年前，基于Pb(ml1 / 3nb2 /3)03 （PMN）的弛豫铁电体被发现后，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。然而，新型pmn型弛豫剂的发展受到其化学顺序明显的“冻结”性质的严重阻碍，这些化学顺序被认为是惰性的，对热处理没有反应。无法修改纳米级阳离子的顺序也使得试图表征局部原子结构或理解和模拟它们的弛豫反应变得复杂。通过对PMN弛豫剂家族的钽酸盐成员Pb(Mg1/3Ta2/3)03及其与PbZrO3的固溶体进行的实验，Davies教授已经确定了可以诱导化学有序畴大小发生两个数量级以上变化的热条件。与其他类型的钙钛矿弛豫剂相比，他还发现这些大域PMT系统的电子性质保持了弛豫剂类型的响应。这些新的观察结果不能与目前接受的pmn型体系结构的“空间电荷”模型相协调，而是支持阳离子顺序的“随机位点”模型。利用透射电镜、x射线和中子衍射的实验将用来表征大域体系的局部化学和结构。介质响应和铁电特性将被测量。其中一些实验将与宾夕法尼亚州立大学的克莱夫·兰德尔教授合作进行。Davies教授发现的改变阳离子顺序的方法为弛豫铁电体PMN家族开辟了一条新的研究途径。在这个更新项目中，先前项目的发现将用于开发一类新的大域、化学有序的铌酸盐、钽酸盐和钨酸盐弛豫剂，这些弛豫剂将比现有的弛豫剂具有更好的性能。与宾夕法尼亚州立大学Clive Randall教授的合作将提高PI小组的实验能力

Davies9809035Following their discovery over thirty five years ago, relaxor ferroelectrics based on Pb(Mg1/3Nb2/3)03 (PMN) have attracted widespread interest for applications in multi-layer capacitors, transducers, electro-optic devices, and thin film memories. However, advances in the development of new PMN-type relaxors have been severely impeded by the apparent "frozen" nature of their chemical order, which has been assumed to be inert and unresponsive to thermal treatment. The inability to modify the nano-level cation order has also complicated attempts to characterize the local atomic structure or understand and model their relaxor response. Through experiments conducted on tantalate members of the PMN family of relaxors, Pb(Mg1/3Ta2/3)03 and its solid solutions with PbZrO3, Professor Davies has identified thermal conditions that can induce more than two orders of magnitude changes in the size of the chemically ordered domains. In contrast to other classes of perovskite relaxors, he has also found that the electronic properties of these large domain PMT systems retain a relaxor type response. These new observations cannot be reconciled in terms of the currently accepted "space charge" models for the structures of the PMN-type systems, and instead support a "random site" model for the cation order. Experiments using TEM and X-ray and neutron diffraction will be used to characterize the local chemistry and structure of the large domain systems. The dielectric response and ferroelectric properties will be measured. Several of the experiments will be carried out in collaboration with Professor Clive Randall of the Pennsylvania State University.%%%Professor Davies' discovery of methods to modify the cation order opens a new avenue of research for the PMN family of relaxor ferroelectrics. In this renewal project, the findings from the previous project will be utilized to develop a new class of large domain, chemically ordered niobate, tantalate, and tungstate relaxors that will have improved properties over those currently available. Collaboration with Professor Clive Randall of the Pennsylvania State University will enhance the experimental capability of the PI's group.***