A static defect simulation study was made of the behavior of impurity-vacancy dipoles, dimers and trimers in crystals of La-doped material. The intermediate phases of the aggregation process could not be identified by using conventional methods. The results indicated that dimers of 2 different impurities could form, and that simple dimers with 2 dipoles of the same impurity ion frequently formed first. The calculated binding energies depended upon the ionic radius of the impurities, and revealed a preferential order for the formation of dimers and trimers. It was noted that the probability of dimer formation from 3 simple dipoles was greater than that from one dimer and one dipole.

S.S.De Souza, A.R.Blak: Radiation Protection Dosimetry, 1996, 65[1-4], 131-4