TECHNICAL: Hyperfine methods such as Nuclear Magnetic Resonance, Mossbauer, and Perturbed Angular Correlation (PAC) spectroscopies are sensitive to changes in electronic and magnetic structure within about 1 nm of the probe atoms that are used by the techniques. Hyperfine methods are therefore capable of detecting local atomic jumps. As a consequence, hyperfine methods have the potential to allow researchers to determine operative diffusion mechanisms in ordered alloys and to study atomic motion in nanocrystalline materials. At present, complications in analysis of data obtained by the hyperfine methods hold back widespread application of these techniques in studies of diffusion. The complications arise in the development of stochastic models that connect jumping of atoms to the time varying interactions they induce. PIs will expand on the approach set forth by Winkler and Gerdau to integrate the calculation of theoretical spectra for the hyperfine methods. In the past, constraints on computational power have required researchers who use Winkler and Gerdau's approach to perform time consuming activities such as (1) reducing large matrices analytically using symmetry arguments or (2) developing analytic approximations to numerical solutions of matrix eigenproblems. Modern computers are powerful enough that one can now incorporate numerical solution of the stochastic models directly into least-squares-fitting software for analyzing spectra directly from the stochastic model. Computer code that is sufficiently general to support stochastic models for all types of hyperfine interactions and for nuclei with any spin state will be developed, and aid cyberinfrastructure (CI) development. The code will allow calculation of theoretical spectra for the hyperfine methods that can be used in least-squares-fits of experimental data. In addition to helping in data analysis, the computer code will support simulation of spectra under varying experimental conditions such as for different crystal structures, defect models, compositions, temperatures, and diffusion mechanisms. A significant portion of the proposed work will utilize simulations to determine under what experimental conditions one can use hyperfine methods to distinguish one type of diffusion mechanism from another in ordered alloys. NON-TECHNICAL: The movement of atoms in solids is of fundamental importance in selection and processing of materials. While the emphasis of this work will be on diffusion in intermetallic compounds, the ability to quickly develop stochastic models for analysis and simulation of diffusion would benefit researchers interested in ceramic and semiconducting materials as well. Moreover, it would be beneficial for studies of atomic motion in nanoparticles and for studies of spin fluctuations.
