Acquisition of an X-Ray CCD Defects System for Materials Research at Advanced Photon Source
H. H. Chen,* T.C. Chiang, H. Hong, R. Broach
National Science Foundation, DMR 98-02643 EQ.; Illinois Board of Higher Education; UOP LLCGFT (In cooperation with the Materials Research Laboratory)

NSF has provided an equipment grant, along with financial contributions from the state of Illinois and UOP LLC, to procure and develop a crystallography facility at the UNICAT organization. This facility includes an analytical x-ray CCD system, a 3-axis goniometer, a computer workstation, and a comprehensive software package for data acquisition and crystal structure determination. The CCD system will enhance our scientific project in three main areas: (1) microcrystal diffraction, (2) small-angle scattering, and (3) time-resolved surfaced interface scattering studies.

Determination of the Atomic Mechanism and Structure 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 and diffuse scatteray studies of lead-magnesium-biobate (PMN) and PMN-PbTiO3 solid-solution single crystals were carried out to study its superstructure. Ordering was observed by the presence of 1z(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 existance of weak spots at the face-centered locations representing in-phase tilt of the oxygen tetrahedra. Complex behavior in the temperature dependance of diffuse intensities suggests the interplay of various physical origins involving soft phonon modes, static displacements, and chemical ordering.

Development of Advanced Photon Source Beamlines for Scattering Science
H. H. Chen,* H. Hong, P. Jemian, 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, Mossbauer effect, diffuse scattering, and macromolecular crystallography. H. Chen is the director of this APS beam-line development project.

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 and Oak Ridge National 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.

Kinetics and Microstructures of Nonequilibrium Materials
P. Bellon,* R. Enrique, J.-M. Roussel, 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 and microstructures in nonequilibrium materials and (2) to investigate the consequences for the microstructure-properties relationship in these materials. Behaviors currently being investigated by atomistic computer simulations, theory and experiments are: the coarsening of precipitates during isothermal annealing, two-phase dynamical equilibrium in alloys under irradiation and under plastic deformation. In the second situation, we have determined that irradiation can induce self-organization of the compaction field at a nanometer scale.

Mesoscale Materials Physics-Dynamics and Microstructural Evolution
H. Chen,* J. S. Chung, L. Basile, in collaboration with G. E. Ice, D. E. Jesson, J. D. Budai, B. C. Larson at ORNL
U.S. Department of Energy, LM 4500010395 (In cooperation with the Materials Research Laboratory)

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.

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. Ball milled powders, in particular, are analyzed using atom probe field ion microscopy. This reveals the characteristics of atomic mixing at the nanometer scale as a function of the milling temperature. This is combined with modeling and computer simulations to rationalize existing behavior and to anticipate possible new microstructures or properties.

Molecular Dynamic Simulations of Phase Transformations
J. Kieffer,* L. Duffrene
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.

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 (chemical and magnetic) exists in high-temperature alloys can be probed by diffuse scattering experiments. We develop and apply a first-principles theory of alloys to compare directly and explain experimental data 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 and providing valuable guidance in the design of new and improved alloys, representing 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.