Kinetics of Interfaces in Nonequilibrium Materials
P. Bellon,* R. Enrique, D. Le Floc'h, S. Zghal
U.S. Department of Energy, DE-FG02-96ER45439 (In cooperation with the Materials Research Laboratory)

The goals of this study are (1) to develop the basic understanding of the behavior of interfaces in nonequilibrium materials and (2) to investigate the consequences for the microstructure-properties relationship in these materials. Two behaviors are currently being investigated by atomistic computer simulations and experiments: the coarsening of ordered domains during isothermal annealing and two-phase dynamical equilibrium in alloys under irradiation. In the second situation, we have determined that irradiation can induce a nonequilibrium roughening as well as a nonequilibrium faceting of precipitates at steady-state.

Mesoscale Phase Separation in Alloys under Plastic Deformation
P. Bellon,* F. Wu
National Science Foundation, DMR 97-33582

Severe plastic deformation can force immiscible elements into solid solution, as observed during low-temperature ball milling of Cu-Co or Cu-Ag powder blends. At moderate milling temperatures, however, dynamical phase separation is expected to take place at a mesoscale. We are developping a program that uses analytical techniques with atomic resolution in order to elucidate the mechanisms controlling such transformations. This is combined with modeling and computer simulations to rationalize existing behavior and to anticipate possible new microstructures or properties.

Displacive Transformation in Ceramics
H. H. Chen,* V. Gosula, A. Tkachuk
U.S. Department of Energy, DE-FG02-96ER45439; Illinois Board of Higher Education HECA Grant (In cooperation with the Materials Research Laboratory)

This is a comprehensive interdisciplinary program of basic research on displacive transformations in ceramics. The ultimate aim is to raise the level of understanding of these transformations to that comparable with martensitic transformations in metallic systems. The program involves studies concerning precursor phenomena and phonon effects, elasticity properties, transformation crystallography, static displacements, chemical and structure ordering, and kinetics. Systems currently being studied are KNbO3, PbTiO3, and BaT:O3, as well as relaxor ferroelectrics PMN, PST, and PLZT.

Development of Advanced Photon Source Beamlines for Scattering Science
H. H. Chen,* H. Hong, P. Jemtan, P. Zschack, G. Kavapetrova, A. Tkachuk, T. Gungoren, Z. Wu
Illinois Board of Higher Education HECA Grant; U.S. Department of Energy, DE-FG02-96ER45439; UOP Corp.; National Institute of Standards and Technology (In cooperation with the Materials Research Laboratory)

The Materials Research Laboratory is engaged in a collaborative effort with personnel from the Oak Ridge National Laboratory, National Institute of Standards and Technology, and UOP Research Inc. for the development of two beam lines of the Advanced Photon Source (APS) being constructed at the Argonne National Laboratory. The foci of this effort are to do research and to educate new generations of scientists and engineers at the cutting edge of the science and engineering in various disciplines. Particular efforts presently underway and planned are in surface/interface diffraction, magnetic scattering, inelastic scattering, Mössbauer effect, diffuse scattering, and macromolecular crystallography. H. Chen is the director of this APS beam-line development project.

Determination of the Atomic Mechanism Evolution of Relaxor Ferroelectrics
H. H. Chen,* V. Gosula, A. Tkachuk
Illinois Board of Higher Education HECA Grant; U.S. Department of Energy, DE-FG02-96ER45439 (In cooperation with the Materials Research Laboratory)

Anomalous x-ray scattering studies of a lead-magnesium-biobate (PMN) single crystal were carried out to study its superstructure. Ordering was observed by the presence of 1/2(111) type superlattice peaks. By tuning the energy of the synchrotron radiation to values close to the Pb LIII absorption edge, the superstructure was shown to include Pb, either by atomic exchange or large displacements. Recent synchrotron x-ray data show the Bragg peak intensities changed not only with temperature but also with aging time. Further work is needed to separate these two effects and to understand the ordering-temperature relationship.

In Situ Scattering Studies of Crystallization of Zeolites
H. H. Chen,* S. Han
UOP Research Center Grant; U.S. Department of Energy, DE-FG02-96ER45439 (In cooperation with the Materials Research Laboratory)

Zeolites find wide applications in petrochemical industries owing to their unique properties, such as absorbents, catalysts, and ion exchangers. Many studies have concentrated on the synthesis of new zeolite types and possible applications for zeolites. The underlying molecular events which govern crystallization are still poorly understood. With the brilliant synchrotron radiation source at APS available as well as state-of-the-art position-sensitive detectors, it becomes possible to carry out the in situ studies using SAXS and WAXS techniques to monitor the whole process of zeolite crystallization, with the precursor gel transformation monitored by SAXS and crystallization by WAXS simultaneously.

Mesoscale Materials Physics-Dynamics and Microstructural Evolution
H. Chen,* in collaboration with G. E. Ice, D. E. Jesson, J. D. Budai, B. C. Larson at ORNL
Subcontract from Oak Ridge National Laboratory, DOE-BES

The goal of this project is to provide a fundamentally new understanding of the physics of mesoscopic structure and microstructural evolution of materials at length scales of tenths to tens of microns. Examples are the structure and dynamics of grain boundaries, dislocations, inclusions, and microstructural inhomogeneities at these length scales. High-brilliance, third generation synchrotron sources now provide an unprecedented opportunity to address this emerging area using ultrahigh spatial resolution x-ray diffraction probes. Microbeam x-ray diffraction will allow three-dimensional mapping of materials properties, including local strain and orientation, with spatial resolution previously not possible.

Theory of Compositional Ordering in Ternary Metallic Alloys
D. D. Johnson,* F. J. Pinski, J. B. Staunton
U.S. Department of Energy, DE-FG02-96ER45439 (In cooperation with the Materials Research Laboratory and Sandia National Laboratories)

The degree to which ordering exists in high-temperature alloys can be probed by diffuse scattering experiments in which pair-correlations for compositional and/or magnetic order are measured. We will develop and apply a first-principles theory of alloys which directly determines these correlations, based on the underlying electronic and magnetic interactions. For the first time, the results of the scattering experiments can be related directly to the electronic structure of metallic alloys, thereby elucidating the microscopic reasons for the structural ordering. Identifying the underlying mechanisms responsible for the observed short-range order provides valuable guidance in the design of new and improved alloys and represents a significant advance in alloy theory.

Thermodynamic Phase Stability of HCP Al-Ag Alloys
D. D. Johnson*
ALCOA Science and Technology Center

Monte Carlo simulation using formation energetic calculated from a first-principles DFT method on the fully ordered, partially ordered, and disordered phases are being used to distinguish between proposed (but conflicting) chemical configuration determined via x-ray and transmission electron microscopy data.

Electronic and Energetic Properties of Materials
D. D. Johnson*
University of Illinois; U.S. Department of Energy, DE-FG02-96ER45439 (In cooperation with the Materials Research Laboratory)

Within a Green's function formalism, electronic density functional theory (DFT) techniques are used to investigate disordered, partially ordered, and fully ordered phases of multicomponent alloy systems. The underlying electronic origin of various materials properties (electronic, magnetic, thermodynamic, elastic) are then determined. Additional schemes are being developed to investigate larger-scale phenomena, such as microstructure and kinetics, which are ultimately based on such DFT results, thus allowing a connection of length scales: micro- to macroscale.

Molecular Dynamic Simulations of Phase Transformations
J. Kieffer,* L. Duffrène
Saint-Gobain Recherche

Large-scale molecular dynamic simulations of inorganic compounds are carried out to study the mechanisms of phase transformations. Phase transitions are induced by simulated pressure or temperature changes. The unstable modes of motion on a local scale are identified by Fourier filtering particle trajectories and by performing normal mode analysis on static structure. Because of the size of the systems, it is possible to study the propagation of transformation fronts and the formation of domains. This research targets issues which arise in conjunction with wear-resistant hard coatings, high-temperature structural ceramics, amorphization under pressure, and relaxor ferroelectrics.