Lattice relaxation around interstitial hydrogen in aluminium

Abstract

The lattice deformation in a simple metal host due to an interstitial hydrogen-like impurity is studied by extending the jellium density approximation of Popovic et al. (1976) to calculate displacing forces and the method of lattice statics to find equilibrium. The validity of the approach is discussed in the framework of the perturbed electron liquid formalism. It is shown, in particular, that the method is incomplete for the long-wavelength components of the strain field, a generalisation of the earlier result concerning the special case of linear screening. In determining the volume dilatation, the 'slope theorem' connecting density distribution with the derivative of the impurity energy in jellium, recently derived by Stott and Zaremba (1980), proves to be essential. The energy of lattice relaxation around a tetrahedral interstitial is found to be -0.18 eV, the heat of solution is 0.71 eV, near to the experimental value (0.66 eV). The energy minimum is at the tetrahedral site, but the barrier is extremely low so that the energetics seem to allow an almost free motion of the proton along the cubic diagonal. The individual displacements of near neighbours are in reasonable agreement with the available experimental data.