Change of conduction mechanism with gamma dose of irradiated borosilicate glasses containing copper ions

The d.c. electrical resistivity of sodium borosilicate glasses containing copper ions has been measured at the temperature range 300–623 K before and after gamma irradiation. The results obtained indicate that conduction may proceed ionically for the unirradiated glasses, with an activation energy in the range 23–24.2 Kcal/mol. Relatively low gamma doses (3.6–25 Mrads) induce two regions, separated at a critical temperature (T_c), of different activation energies. An activation energy E₁, 3.4 Kcal/mol, in the temperature range from 300–370 K, and E₂ 16.8–20.9 Kcal/mol, in the range of higher temperatures. The mechanism suggested is that the ionic conduction is replaced by an electronic one up to about 370 K then seems to be replaced at higher temperature region by ionic-like mechanism which can be expressed by exciton-like process. High gamma doses (28.33 M rads) cause the glasses to have activation energy ranges between 19.9–22.7 Kcal/mol, which may substantiate the predominance of the proposed ionic-like mechanism.The transition region around T_c seems to be divided into three regions, precritical, critical and post-critical.