In-situ X-ray analysis and smart materials
Smart materials have the capability to both sense and respond with some useful action to changes in the physical and/or chemical conditions of their surroundings. The materials used in smart devices are highly responsive because of some inherent, persistent 'disequilibrium' related to their crystallographic state; they are, in a sense, 'quivering inside' in anticipation of a state change initiated by relatively subtle changes in their physical and/or chemical environment. Smart materials such as piezoelectric lead-zirconate titanate [Pb(Zr,Ti)O3] and the shape-memory alloy Nitinol [NiTi] possessing active domain walls, and two phase transformations which also allow for the ability to further 'tune' a smart response of the materials. They typically possess a structural or morphotropic phase boundary [MPB], separating two phases of distinctly different symmetry. Compositions from these solid solutions remaining active and responsive over a wide range of temperatures.
The relaxor ferroelectric materials are a special class of ferroelectrics. They exhibit a more diffuse temperature dependence of their dielectric properties as they undergo the paraelectric - ferroelectric phase transition over a range of temperatures as opposed to the relatively sharp transition that is manifested for the 'normal' ferroelectrics. Materials of this type tend to have exceptionally high dielectric, electromechanical, and electrooptic properties in the vicinity of this phase transition. R. Guo (Penn State) presented the crystal structure analysis and the identification of polarization mechanisms in relaxor ferroelectric tungsten-bronze materials. This family of materials is well-suited for smart applications due to their ferroelectric nature and, the presence of both a paraelectric - ferroelectric phase transition and a morphotropic phase boundary [MPB].
T. Egami (U of Penn) uses pulsed neutron atomic pair-density function (PDF) analysis to probe the local ferroelectric structure of oxides. The results indicate that on a local scale the atomic structure of these materials is highly aperiodic, in contrast to the information typically obtained by standard crystallographic diffraction.
Q. Zhang (Penn State) discussed the first discovered relaxor ferroelectric polymer. The exceptionally high electrostrictive strains produced in these materials have been attributed to their relaxor nature, a significant lattice strain difference between polar and nonpolar regions, and the polymer's inherent capacity to accommodate larger strains without experiencing mechanical failure. S. Pilgrim (Alfred U.) spoke about the development of electroactive smart materials for control systems of communications satellites and interplanetary probes. Relaxor electrostrictive materials with transition temperatures within the range of 30 - 100 K are desirable for these purposes.
W. Soffa (U. of Pittsburgh) addressed the relationship between microstructure, defect-structure and properties of ferromagnetic alloys which are responsive to changes in magnetic field. The identification of the effects on domain structure and wall mobility have become key elements in the development of magnetic smart materials. J. Levy (U of Pittsburgh) spoke on high resolution optical techniques for real-time imaging of domain wall movement in activated ferroelectric thin films. P. Phulé (U of Pittsburgh) described magnetorheological (MR) smart fluids that undergo a rapid and significant increase in viscosity with the application of an external magnetic field. Even though this material is referred to as a 'fluid,' it assumes a periodic structure that can be probed by X-ray diffraction. With the removal of the magnetic field, the material reverts back to its fluid form very much resembling ordinary paint in terms of its viscosity and physical appearance.Jayne Giniewicz
From the ACA Newsletter, Winter 1998