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Displacive phase transformations can be Workshop on First-Order either first- or second-order; the former are Displacive Phase usually subdivided into strong, moderate, Transformations and weak. Examples of second-order Proceedings published in Materials transformations are the ferroelectric insulaScience & Engineering, Volume A127, tors strontium titanate and barium niobate. No. 2, August 1, 1990 Strong first-order transformations appear A workshop on First-Order Displacive Phase Transformations was held under the auspices of the Materials Sciences Division, Office of Basic Energies Sciences, U.S. Department of Energy, at the Claremont Resort Hôtel—reputedly the largest wood frame structure in the world—in Oakland, California, on October 24-28, 1988. It was co-chaired by Lee E. Tanner of Lawrence Livermore National Laboratory and by M. Wuttig of the University of Maryland. The proceedings, with a long but not uncommon delay of over 21 months, appeared last August as a full issue of Materials Science & Engineering. Displacive phase transformations in solids are fascinating phenomena which hâve, so far, refused to yield to a thorough basic understanding, even though they are of fundamental importance in many materials applications and hâve been the subject of intensive investigationsexpérimental and theoretical, basic and applied, fundamental and phenomenological—for well over a century. Thèse transformations proceed by means of a coopérative displacement of the atoms from their original lattice sites: the displacements are a sizable fraction (approximately 10%) of the interatomic distance, very large in comparison with the ordinary lattice vibrations. During the transformation the crystal symmetry is profoundly altered, even though there is essentially no change in atomic order or chemical composition of the material.
in steels—the primordial martensites—as well as in some ceramics (e.g. zirconia). Moderate first-order transformations are présent in a large variety of alloys (the socalled shape memory alloys): In-Tl, Fe-Pd, Ni-Ti, Au-Cd, and (the prototypical example) the ft phase of Ni-Al. Finally, weak (almost second-order) first-order displacive transformations appear, for instance, in the A15 intermetallic superconductors (e.g. Nb3Sn and V3Si) in In-Tl solid solutions. The workshop, which aimed at crossdisciplinary stimulation and fertilization, could not completely eliminate the branching always présent in most fields of materials science; whereas for thèse transformations the theorist tends to study the second-order or weakly first-order phenomena, emphasizing a search for universality and common trends, the applied scientist is mostly concerned with spécifie Systems and well-defined phase diagrams with particular purposes in mind (thèse most frequently involve the alloys characterized by strong first-order effects); whereas the physicist mostly looks at precursors and order parameters which are susceptible to sensible—albeit not simple— mathematical formulations, the materials scientist examines the apparen
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