Electrical properties of bismuth nanocrystal-glass composite

Composites of bismuth nanocrystals and glass matrix have been obtained from Bi_0.33Ge_0.67O_1.84 and Bi_0.57Si_0.43O_1.72 glasses as a result of thermal treatment in hydrogen atmosphere. We have shown that the temperature dependence of the conductivity of bismuth germanate glass containing Bi nanocrystals, reduced in hydrogen exhibits crossover from T^−1/4 to T^−1/2 dependence in the temperature range between 170 and 190 K. Characteristic parameters describing conductivity were determined and their values were discussed within the models describing conductivity in granular metals. Conductivity in Bi-GeO₂ system may be described within the model of variable-range hopping between localized centers including Coulomb gap. On the other hand, in Bi-SiO₂ system the ES model is not a good explanation of conductivity. We suggest that Zvyagin’s model of conduction by hopping via virtual states (no Coulomb gap effects) may quite well describe conductivity in this system with high concentration of grains.