Linear and nonlinear impedance of alkali and iron doped silicate-lead glasses

Linear and nonlinear impedance was studied for lead-silicate glass samples doped with iron ions and alkaline oxides. The compositions of glasses were as follows: (in %mol) 50% SiO2, 25% PbO, 15% Fe2O3 and 15% one of alkaline oxides: Na2O, K2O, Li2O. All samples were prepared by the conventional melt quenching technique. The substrates were powdered in a mortar and melted in alumina crucibles. The melting of glass containing lithium ions was conducted in air at 1373K. The glasses with potassium ions and sodium ions were melted at 1473K. The melts were poured out on plate heated up to 673K and formed into small circular-shaped pellets (about 1,5 mm thick and 20 mm in diameter). Next glasses were annealing at  the 673K and cooling with furnance. After a polishing, golden electrodes were evaporated at both sides of  preheated samples in vacuum, for the electrical conductivity measurements. The linear and nonlinear impedance spectra were measured in the frequency range of 1 mHz to 1 MHz and in the temperature range of 153K to 483K by Concept 40 broadband dielectric spectrometer. The nonlinear electrical properties were measured also as a function of A.C. voltage in range of 0.01 - 1 Vrms.