Electrical conductivity and viscosity of phosphate glasses and melts

Phosphate glasses are of great interest for basic research and for special applications in various fields as technical and optical glasses. Metaphosphate compositions with PO4-chain structure are mostly used. The cations have a significant effect on the properties of the glasses and melts. This was studied in more details. High purity metaphosphate glasses, Mn(PO3)n with M = Na+, K+, Zn2+, Mg2+, Ca2+, Sr2+, Ba2+, Al3+ and Fe3+, were prepared and the optical and thermal properties were measured with different methods. The electrical conductivity of glasses and melts is the property of great practical importance. It was determined by impedance spectroscopy in a wide temperature range from 300 to 1250 °C in frequency range of 0.1 Hz to 6 MHz. The electrical conductivity of alkaline earth phosphate glasses and melts increases with increasing ion radius of the cation. NaPO3 and KPO3 glasses and melts have much higher conductivity. Viscosity measurements were carried out from transformation temperature, Tg, to the melt. The measured data were fitted and the activation energies of the conductivity and viscosity were calculated. Simple exponential behavior was found at temperatures below Tg, but above Tg only in very narrow temperature range. The relation between conductivity and viscosity was considered.