The vacancy formation and motion energies in gold

Abstract

A theory is presented which predicts the vacancy loss to fixed sinks during a quench. For quenches in which the temperature decreases linearly with time, the fraction of the vacancies lost is shown to depend only on the product D _q T _q, where D _q is the vacancy diffusion coefficient at the quench temperature T _q, and τ_q is the quench time. The theory is used to analyse the results of a series of quenches having values of T _q and τ_q in the ranges 470°c < T _q < 1030°c and 0·025 sec < τ_q < 4·3 sec. Both 0·016 in. and 0·002 in. diameter gold wires were studied and found to yield an effective formation energy of about 0·90 ev for the fastest quench times. For any value of the activation energy Q for self-diffusion in the neighbourhood of 1·8 ev, the quenching data are consistent with the theory only for one pair of values of E _M and E _F. With Q = 1·81 ± 0·02 ev it is found that E _F = 0·98 ± 0·02 ev and E _M = 0·83 ± 0·04 ev. The fact that the vacancy loss depends only on D _q T _qτ_q is confirmed over a range of a factor 10⁵. Furthermore, the dependence of the vacancy loss on the magnitude of D _q T _qτ_q shows that the surfaces and grain boundaries of the specimens absorb only a small fraction of the total number of vacancies lost in the quench. As vacancy clustering and precipitation can also be eliminated, it is concluded that dislocations or sub-grain boundaries are probably the dominant sinks at high temperatures.