Atoms, Defects and Diffusion in Solids

Collins Research Group
Hyperfine Interactions Laboratory
Department of Physics and Astronomy, Washington State University, Pu ll man, WA, 99164-2814, USA
Welcome! We study the local structure of ordered solids through measurements of nuclear hyperfine interactions. Interactions between nuclear quadrupole moments and electric field gradients (EFG) "flag" local environments of radioactive probe atoms, including neighboring point defects. Signal amplitudes give site fractions of probes on the various sites from which can be determined defect concentrations and thermodynamic properties that include site enthalpies of probe atoms, formation and migration enthalpies of defects, and interaction enthalpies with solute atoms. Atom movement at jump frequencies in the the MHz to GHz range gives rise to measurable nuclear relaxation. We mostly study intermetallic compounds but methods are applicable to all crystalline solids. We especially apply perturbed angular correlation of gamma rays (PAC), and are essentially the only PAC group actively studying solids in North America. Current interests:

Lattice locations and energies of solutes in compounds. We measured how dilute solutes "switch" from one site to another in response to changes in temperature or composition through temperature dependences of site fractions. See our studies of indium solutes in Laves GdAl₂ and Ni₂Al₃ phases in the"papers" pages. More recently, we have measured enthalpy and entropy differences of solutes on inequivalent sites of a single element in compounds. The measurements can directly give the enthalpy difference of a solute atom on two sites with a precision of 0.01 eV, as shown in our study of indium solutes on inequivalent Al-sites in compounds having the Al3Ti and Al3Zr crystal structures. These are classic two- and three-level systems for solute atoms.
Diffusion of probe atoms: We have shown that jump frequencies of PAC probe atoms can be measured through nuclear quadrupolar relaxation. Such relaxation occurs when probe atoms jump among lattice sites having different orientations or magnitudes of electric field gradients. Jump frequencies in the MHz to GHz range can be determined by fitting observed nuclear relaxation. Temperature dependences yield jump-frequency activation enthalpies as precise as those obtained through the standard method of measuring diffusion constants through measurements of concentration profiles by sectioning--but with much less effort. See our papers on diffusion.

Click below to learn more about PAC and to download papers. Contact me for more information, to participate in our work, or to explore collaboration in a project.

What we do	Who we are
PAC spectroscopy Other methods Useful links	Research opportunities Sources of support
Papers 2006-2010 Papers 2001-2005 Papers 1995-2000 Selected publications to 1995	Powerpoints and research nuggets Meeting abstracts Pics
PAC links worldwide	Seventh International Conference on Diffusion in Materials, Lanzarote, Canary Islands, October 2008 11th Annual Meeting, Northwest Section of the American Physical Society, Vancouver, BC, May 2009 Diffusion in Solids and Liquids Conference, Rome, June 2009 Diffusion Fundamentals Conference, Athens, August 2009 Diffusion, Stresses and Segregation, Moscow, June 2010

June 2009. Send comments and suggestions to Professor Gary S. Collins at collins at wsu.edu. There have been roughly 70000 visitors since 1998. Material in this web site is based in part on work supported by the Metals Program of the National Science Foundation under Grant DMR 05-04843 and predecessor grants, for which we are most grateful. Additional support comes from the Praveen Sinha Fund for Physics Research. Any opinions, findings, and conclusions or recommendations expressed in these pages are those of the author(s) and do not necessarily reflect views of the National Science Foundation or of the Praveen Sinha Fund. Copyright© Gary S. Collins, 1995 and later years. Disclaimer.

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