Chemical and Thermal Modification of PMN-Type Relaxor Ferroelectrics

继35年前他们的发现之后，基于Pb1/3Nb2/3(PMN)03(PMN)的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。然而，新的PMN类弛豫剂的发展已经严重阻碍了它们的化学秩序的明显的“冻结”性质的发展，这种化学秩序被认为是惰性的，对热处理没有反应。无法改变纳米级的阳离子顺序也使表征局部原子结构或理解和模拟其弛豫响应的尝试变得复杂。戴维斯教授通过对弛豫剂PMN家族中的钽酸盐成员、Pb(Mg1/3Ta2/3)03及其与PbZrO3的固溶体进行的实验，确定了可以导致化学有序磁区大小发生两个数量级以上变化的热条件。与其他类别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型响应。这些新的观测结果不能用目前公认的PMN型系统结构的“空间电荷”模型来协调，而是支持阳离子有序的“随机位置”模型。使用电子显微镜、X射线和中子衍射的实验将被用来表征大磁区系统的局域化学和结构。将测量其介电响应和铁电性能。几个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。戴维斯教授发现了改变阳离子顺序的方法，为研究弛豫铁电体的PMN家族开辟了一条新的途径。在这个更新项目中，前一个项目的发现将被用来开发一类新的大磁区、化学有序的铌酸盐、钽酸盐和钨酸盐弛豫材料，这些材料的性能将比目前可用的材料有所改善。与宾夕法尼亚州立大学的克莱夫·兰德尔教授的合作将增强PI团队的实验能力。

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.***