Conductivity and dielectric relaxation in sodium borosulfate glasses

Sodium borosulfate glasses having composition xNa(2)SO(4)center dot(30-x)Na2O center dot 70B(2)O(3) (1.5 <= x <= 9.0 mol%) were prepared by melt-quenching technique. The influence of Na2SO4 on physical and thermal properties has been interpreted using density, molar volume and DSC data. The decrease in glass transition temperature (T-g) with increase in Na2SO4 content indicates that the average chain length of the host glass matrix decreases. The temperature-dependent conductivity data of the above glass samples have been obtained using impedance measurement in the temperature range 523-593 K and the frequency range 20 Hz to 1 MHz. The do electrical conductivity (sigma(dc)) follows Arrehenius relationship and activation energy is 0.83 +/- 0.03 eV for ionic migration. The do conductivity (at 553K) of the glass with x=1.5 mol% is 2.08 x 10(-4) Omega(-1) m(-1) and it is 6.16 x 10(-4) Omega(-1) m(-1) for x=9 mol%. The ac conductivity obeys Almond-West type power law behaviour: sigma(omega) = sigma(dc) + sigma(ac)(omega) = sigma(dc) + A omega(s). The behaviour of the complex permittivity, dielectric loss and dielectric modulus as a function of frequency was also investigated. An excellent time-temperature superposition in the imaginary part of dielectric modulus (M '') confirms that the dynamical processes are temperature independent and is also an indicative of a common ion transport mechanism. (C) 2008 Elsevier B.V. All rights reserved.