AN EXTENDED POLARIZABLE POINT ION MODEL FOR SCHOTTKY DEFECTS

The polarizable point ion model for Schottky defects is extended to include the effects of induced quadrupoles in region 1. Schottky defects in AgCl are studied using this model. It is found that it is important to include induced quadrupole moments in any theoretical treatment of charged point defects in ionic crystals. Quadrupolar deformations make sizable contribution to the defect energy which ranged from -0.2 to -0.4 eV in the case of the cation vacancy over the range of anion quadrupole polarizabilities studied. The work further points to the relative significance of chlorine ions in respect of the quadrupole distortions.