AC conductivity of vanadium phosphate glasses

Measurements have been made on different composition V 2 O 5 -P 2 O 5 glasses in the frequency range 10 2 Hz to 10 5 Hz and in the temperature range 77K to 300K, for different times of annealing up to 300 degrees C. No effect of annealing was observed, indicating that the frequency-dependent AC conductivity is an intrinsic property of the material. A comparison of the measured AC conductivity sigma ( omega ) has been made with some of the models of hopping conductivity proposed earlier in the literature. It is observed that in vanadate glasses the measured AC conductivity sigma ( omega ), over the entire frequency and temperature region can be explained reasonably well by assuming two contributions sigma 1 ( omega ) and sigma 2 ( omega ) to the measured sigma ( omega ). The first, sigma 1 ( omega ) which dominates at low temperatures, may be due to hopping of carriers near the Fermi level and the second, sigma 2 ( omega ), which dominates at higher temperatures, depending on the frequency of measurement, may be due to the hopping of carriers excited to the conduction band edge and is responsible for the activated dielectric loss peak.