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Diffusion at Grain Boundaries

J. Harding and D. Harris
Department of Physics and Astronomy
University College London

W. Smith
CSE Department, Daresbury Laboratory

The project will use the biased-potential hyperdynamics method of Voter [1] and kinetic Monte Carlo methods to study diffusion processes with rates too low for conventional molecular dynamics to be used. The hyperdynamics methods will be incorporated in the DL_POLY program [2] developed at Daresbury laboratory. The kinetic Monte Carlo methods will be written as a stand-alone program. These programs will then be used to study diffusion problems in grain boundaries in ceramics.

A number of generic problems will be addressed. First, we will obtain values for the effective width of a grain boundary for diffusion (considering how it varies for different boundaries and crystal structures). Second, we will calculate the variation of the diffusion coefficient with boundary tilt angle. In particular, we will consider how the anisotropy of the diffusion coefficient in the boundary varies with tilt angle and how useful it is to consider the boundary as an array of dislocations. Third, we will consider variations of the diffusion coefficient with structure and, for a given structure, the variation with ion size. Finally, we shall calculate the effect of impurities on the diffusion rate and mechanism. In particular, we shall calculate the diffusion rate of dopants in boundaries.

References

[1] A.F. Voter, J. Chem. Phys. 112 (2000) 9599.

[2] T.R. Forester and W. Smith, The DL_POLY Molecular Simulation Package, J. Molec. Graphics 14 (1996) 136.

 
For more information about the work of the Computational Chemistry Group please contact Paul Sherwood p.sherwood@dl.ac.uk.

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