MST-8 People


Name	Steven D. Conradson
Team	Alloy Theory
Position	Technical Staff Member
Phone	(505) 667 9584
E-Mail	conradson@lanl.gov
Research Interests	Application of synchrotron x-ray methods, primarily X-ray Absorption Fine Structure (XAFS) spectrscopy, to determine chemical speciation and local structure in a multitude of systems, especially in the area of actinide environmental chemistry, solution and solid state chemistry, and materials science, but also including catalysts, cuprates, manganites, metals and alloys, ceramics, magnetic materials and heterostructures, etc. Also, the implications of these experimental data in terms of intrinsic nanoscience, collective and cooperative phenomena that result in strong interactions between inhomogeneities in solid solutions that result in composition and fluctuations and corollary nanoscale heterogeneity, which is likely to be a characteristic of complex functional materials that underlies many of their special or unique properties.
Research Highlights	Demonstrated that plutonium contamination in almost all sites at Rocky Flats was in the (IV) valence, indicating that transport was via colloids and not dissolution. This finding was instrumental in setting a limit for residual contamination that reduced the number of waste shipments to WIPP by an amount equivalent to ca. 300M. Identified the adventitious oxygen in PuO2+x as Pu(V)-oxo groups, analogous to solution chemistry, but also that although these result in unusual and continuous chemistry in the system that they do not increase the solubility of the Pu and thus do not increase its potential hazard as a contaminant above that of pure PuO2. Found that delta-stabilized Pu alloys are heterogeneous, with up to 20% of the Pu atoms in materials with low concentrations of Ga or other stabilizers occurring in the Ga-depleted regions as a second ordered structure in the form of nanoscale domains that diffract poorly to negligibly and thus do not give a recognizable signal in diffraction patterns. The collective behavior that fosters this heterogeneity is sufficiently strong that it also appears to be essential in aging processes, where at certain times the aging-induced defects appear to occupy the same volumes that the sigma phase originally did to create an additional type of ordered structure involving one-to-two orders of magnitude more atoms than predicted by other models. Showed that capping the Fe layer in the 110 Cu-Fe (110 ML) system causes the Fe in phase I to be fct and not twinned bcc but that this does not affect the spin ordering, so that the atomic and magnetic structures are decoupled. This is also the case in the 111 system which breaks up the Fe planes with parallel spins.
Education	B.S. Chemistry San Jose State University 1977 Ph.D. Physical Chemistry Stanford University 1983 NIH Post-doctoral fellowship Harvard University 1983-1985 LANL 1985-present
Curriculum Vitæ