Radiation induced capacitance in barium aluminoborate glasses

Impedance analysis (IA) was applied to study the effect of electrically charged radiation-induced point defects on the dielectric properties of barium aluminoborate glasses. Changes observed in the real component ε′ of the dielectric constant after X-ray irradiation have been investigated by comparing the dipolar contributions from the induced electrical charges, with those already present in the glass before irradiation. In this paper the results of impedance spectroscopy are presented and analyzed for the glass systems (1−x)((1/7)Al2O3 · (6/7)B2O3) · xBaO(Ax) and (1−x)((2/7)Al2O3 · (5/7)B2O3) · xBaO(Bx), where x represents the molar fraction of the alkaline earth oxide in the sample for x=0.3(Ax) and x=0.2, 0.3, and 0.4(Bx). It is suggested that the most important contributions in the observed increase of ε′ at room temperature are provided by the dipoles formed by a boron–oxygen hole center and a non-paramagnetic boron electron center (BEC2−, BOHC+), those composed by a BOHC and a neighboring Fe3+ impurity cation which has trapped an electron ([Fe2+]−, BOHC+), and those composed by a BOHC and an alkaline earth electron center (AEEC−, BOHC+). For glasses of high alkaline earth content it was observed a decrease of ε′ and a model is suggested for the mechanism of this behavior.