A DEBYE MODEL FOR POINT-DEFECTS IN ALUMINOSILICATE CRYSTALS

In aluminosilicate lattices, exchanges between silicon and aluminum io ns are expected to originate charged point defects of opposite signs. Thermodynamic arguments, based on a model analogous to the Debye elect rolyte model, allow evaluation of the equilibrium density of defects a s a function of temperature. The electric field of point defects is fo und to be screened by charge distribution even at distances small enou gh to affect the ground-state energy of electrons trapped by the defec t positive charges. Calculations show that large fluctuations of trapp ed electron energy are expected. These results agree with data from th ermoluminescence experiments on different aluminosilicates, which show ed broad distributions of electron traps.