Effect of vitrification suppression on non-linear conduction in vanadium phosphate glasses

The effects of both composition and creation of the crystalline phase in (V2O5)(1-x)(P2O5)(x) glasses, where x = 0.10, 0.15, 0.20 and 0.25, on both I-V characteristic curves and ac conductivity are studied in the temperature range 303-473 K. The I-V characteristics show non-linear behavior below and beyond a turnover point (switching point) characterizing these glasses. This turnover point is shifted towards lower voltage and higher current as the vanadium content, the ambient temperature or the degree of cystallinity in the glass were increased. The results are interpreted according to the Poole-Frenkel emission of electrons under high field between filled V4+ and empty V5+ sites in the region below the turnover point. The conduction in the negative-resistance region (beyond the turnover point) is discussed according to the hopping of electrons between filled and empty sites under high field, joule heating and self-generation of ac signal. The frequency dependence of the ac conductivity satisfies the power law relation, sigma(omega) similar or equal to omega(s), which explains the quantum-mechanical hopping of single electrons in the disordered matrix.