Chemical and Thermal Modification of PMN-Type Relaxor Ferroelectrics

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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.***