The influence of lattice defects on the electrical resistivity of a gold-copper alloy (7 at. % Cu)

Abstract

Lattice defects were introduced in wires of a gold—7 at. % Cu alloy by quenching from 900°C or 450°C or by stretching 15 per cent at — 195°C. The effect of annealing at temperatures up to 300°C on the electrical resistivity was investigated. For comparison the same experiments were carried out on pure gold. In the annealed state short range order exists in the alloy, which causes an increase in the resistivity at — 195°C of about 3 per cent. This order is destroyed both by heating and quenching, and stretching the material; it may be restored by annealing between −40°C and +200°C, by means of a diffusion of lattice defects with an activation energy of 0.60 ± 0.05 eV. From the initial velocities of ordering on annealing after quenching from 900°C and from 450°C, the energy of formation of these defects is found to be 0.93 ± 0.10 eV. After quenching only one recovery step is found; after stretching three different recovery steps may be distinguished. In the first of these steps, between — 195°C and −40°C with activation energy 0.3–0.4 eV, no ordering takes place. This gives an argument against the attribution of this step to double vacancies. The second step (between −40°C and + 100°C) shows the same recovery mechanism as is found after quenching. In the third step, which was not fully investigated, recrystallization takes place.