Mixed dc Electrical Conduction in Zinc Potassium Doped Borate Glasses

A series of borate glass system in the composition (K2O) x -(ZnO)0.5-x-(B2O3)0.5; x=0.08,0.16,0.24,0.32 and 0.40 has been prepared using melt quench technique. The samples were annealed at 453K, to remove any thermal strains present in the glass matrix. The XRD pattern confirms the non-crystalline nature of the glass systems. The room temperature density of the glass samples was measured by adopting Archimedes principle and molar volume estimated. The oxygen packing densities were calculated using molar volume. The room temperature density and molar volume varied non-linearly and appositively with mole fraction of K2O. DC electrical conductivity was estimated in the temperature range 313 K to 473 K by using two probe method. The high temperature activation energy was calculated for T >θD/2 in the light of Mott’s small polaron hopping model. Various small polaron hopping parameters such as small polaron radius, effective dielectric constant, polaron band width, optical phonon frequency, small polaron coupling constant, density of states at Fermi level have been calculated and discussed. The nonlinear variation of conductivity and activation energy with mole fraction of K2O shows the changeover of conduction mechanism taking place in present series of glasses at x=0.24. It is for the first time that two dominant conduction mechanism regimes were observed in potassium-zinc-borate glass systems.