Gorsky relaxation in the presence of traps

Abstract

It has been shown recently that a linear response theoretic formalism leads to a straightforward derivation of the theory of the Gorsky effect at low interstitial concentrations, for arbitrary specimen geometry and applied stress inhomogeneity. We now extend this formalism to the practically important situation in which traps (e.g., N interstitials) inhibit the diffusion of the H interstitials, in order to motivate the experimental application of the Gorsky relaxation technique to the determination of the trap parameters. An explicit calculation is done for a typical specimen geometry, using Schroeder's phenomenological model for diffusion in the presence of traps. Exact expressions are obtained for the anelastic creep function, the relaxation strength and the internal friction. The structure and physical implications of these expressions are discussed using numerical values for the parameters deduced by other methods (in particular, neutron scattering). Noteworthy features of the predicted dynamic response include shifts in the position and height of the Gorsky peak owing to the occurrence of an effective diffusion constant and the difference in the values of the trace of the elastic dipole tensor in the free and trapped states; and an additional Snoek-like contribution due to local free ↔ trapped transitions of the diffusing particles.