Static defect simulations were made of Mg2+-doped material in order to calculate the formation, binding and activation energies of dipolar defects. Another type of dipole configuration was proposed that differed from the well-known impurity-vacancy dipole in alkali halides. Instead of a cation vacancy near to the divalent impurity, an interstitial F atom occupied the center of the cube so as to form an impurity-interstitial dipole. The calculated value of the activation energy (0.661eV) agreed quite well published values for the impurity-vacancy dipole. The calculated activation energy for the impurity-vacancy dipole was 0.864eV. It was suggested that the 2 values were sufficiently near to permit the coexistence of both. The calculated energies also indicated that 3 dipoles could form a trimer without the occurrence of an intermediary dimer.

S.S.De Souza, A.R.Blak: Materials Science Forum, 1997, 239-241, 699-702