Proceedings:

This winter workshop focused on the experimental and theoretical understanding of ferroelectrics. Ferroelectrics are exceedingly useful materials in modern technology, with applications as transducers, actuators, dielectrics, and nonvolatile memories. In addition, they present fundamental problems in the behavior of insulators in electric fields, spontaneous polarization, piezoelectricity, phase transitions, extreme sensitivity to temperature, composition, and pressure. Experimental and theoretical advances in the last decade have stimulated a major resurgence of interest in this classic problem of condensed matter physics. The number of papers in the field has been growing steadily since 1986, and there were more papers published last year in ferroelectrics (over 2000) than in superconductivity.    In 1998, activity received a further boost from the observation of giant piezoelectric response in single crystals of a particular family of single crystal relaxor ferroelectrics. The origin of this behavior is yet to be understood and further significant optimization is likely.

This workshop was the sequel to a series of alternating experimental and theoretical meetings on fundamental issues in ferroelectrics held in Colonial Williamsburg each year since 1990. The workshop jointly addressed experimental and theoretical issues in synthesizing, measuring, understanding, and predicting the behavior of these fascinating materials. A central goal was to assess the state of the field and identify future directions for research.

Key problems addressed included:

• Polarization. It was only recently that a fundamental theory of polarization in solids was developed. Previously there was a mistaken notion that bulk polarization could be found from the charge density. The latter approach is correct only for finite crystals, and then is dominated by surface effects. Questions have also arisen about polarization dependence of the exchange- correlation in Kohn-Sham theory, and several approaches are being explored.
• Mechanisms, properties and dynamics of relaxors. Relaxor ferroelectrics exhibit a characteristic set of static and dynamical properties. Many questions remain regarding a microscopic understanding of relaxor properties and the nature of the ferroelectric transition in relaxors.
• Temperature. New techniques are being developed to study ferroelectric phase transitions and piezoelectricity as functions of temperature using model Hamiltonians and Monte Carlo methods. Questions of interest include temperature dependence of the equilibrium state and dynamical behavior of bulk crystals and interfacial structures in ferroelectric and ferroelastic materials, one example being the transport and pinning of oxygen vacancies along twin boundaries.
• Electric fields. There are significant conceptual and technical problems problems in understanding crystal behavior under finite external macroscopic electric fields.
• Piezoelectricity. With first-principles computations of piezoelectricity, it is possible to obtain the intrinsic response and understand the relative roles of crystal structure and microstructure in producing the measured values. Piezoelectricity is one of the central useful properties of ferroelectrics, and ferroelectrics are widely used in actuators and transducers. Design improvements in materials based on microscopic information can potentially lead to significant improvements in these devices.
• Solid solutions. Most ferroelectrics, including the recently discovered single-crystal piezoelectrics Pb(Mg,Nb)O3--PbTiO3, are complex solid solutions. The nature and effect of medium range and short-range order in these materials can be explored using state-of-the-art spectroscopic techniques, and theoretical modeling presents particular challenges.
• New materials. Compilations of known ferroelectric materials include hundreds of compounds and solid solutions. While many of these are distortions of the perovskite structure, there are a number of other families of oxide ferroelectrics, as well as hydrogen-bonded ferroelectrics, semiconductor ferroelectrics, organics, and other materials. The perovskite structure itself displays an enormous and only partially explored compositional range, and coupled with the fact that ferroelectric properties are very sensitive to composition an effectively unlimited range of tunable properties. This diversity offers virtually unlimited opportunity for exploration in search of new ferroelectrics and related materials with desired properties, including high piezoelectric and dielectric constants.
• Thin films, interfaces and heterostructures. Thin films and related structures are central to electronics applications of ferroelectrics. The synthesis of these structures via MBE, sputtering, and other methods has seen rapid advances, yielding devices of high quality and reproducibility. The properties of these systems are largely determined by surface effects, finite size effects, and the atomic and electronic structure of interfaces between ferroelectrics and metals or ferroelectrics and other dielectrics. Thus, they pose fundamental experimental and theoretical problems, progress in which can contribute in significant ways to technological applications.
• Loss mechanisms, fatigue, and aging. These aspects of ferroelectric materials are crucial for device applications, but their complexity presents both experimental and theoretical challenges. Defect and domain structures appear to play an important role. The electronic structure of these features must be established to predict the behavior of space charge limited currents and dielectric breakdown. The role of disorder has been further explored through studies of dipolar glasses.
• Formation and dynamics of microstructures. Advances in experimental technique and computational modelling are driven by the problem of the characterization and control of microstructures, including twin boundaries, needle domains, and surface structures.

Scientific Advisory Committee:

Organizing committee:

For further information, contact Ronald Cohen or Karin Rabe.