A determination of the binding free energy between vacancies and silicon solute atoms in aluminium using an equilibrium method

The equilibrium vacancy concentration in en aluminiurn-0.28 at. % silicon alloy was determined by measuring the difference between the linear expansion and lattice expansion during heating and cooling between 410 and 640°c. It was found that the defect concentration at 640°c in excess of that at 410°c is approximately 25% greater in the alloy than in pure aluminium. Analysis of the data in terms of the simple Lomer model for solute–vacancy interaction yields a value for the solute–vacancy binding free energy of 0.20 ev. Careful consideration of the possible errors gives an accuracy of ±0.04 ev. The data are not sufficiently precise over a wide enough temperature range to provide a test of the Lomer model.