For Cu and a-phase Cu-Al alloys, the monovacancy formation energies which were in the linear decrease with increasing of the Al concentration were obtained by means of the angular correlation method in positron annihilation. The results showed that the formation energy in concentrated random alloys was due to the averaged potential. The formation energy of the 2nd multivacancy (divacancy mainly) was obtained using data at very high temperatures: 2.20eV for Cu, 2.30eV for Cu-2.0Al.

Study on the Vacancy Formation in α-Phase Cu-Al Alloys by Positron Annihilation. O.Sueoka: Journal of the Physical Society of Japan, 1975, 39[4], 969-75