ANOMALOUS BEHAVIORS OF ELASTIC MODULI, DC CONDUCTIVITY AND OPTICAL PROPERTIES IN MIXED TRANSITION-METAL-ION (20-x) MnO2-xFe2O3-80TeO2 TELLURITE GLASS SYSTEM

Mixed transition-metal-ion xFe(2)O(3)-(20-x) MnO2-80TeO(2) glasses were prepared using melt-quenching method to study the DC conductivity, elastic and optical properties of the glasses. DC conductivity showed a strong increase for x <= 10 mol% Fe2O3 before reaching a saddle-like behavior between 10 mol % <= x <= 15 mol%, followed by a large increase for x> 15 mol%. Longitudinal and shear velocities nu(L) and nu(s) exhibited non-linear behaviors and where bothincreased for x <= 10 mol% with an anomalous drop at x = 15 mol% Fe2O3, followed by a large increase at x> 15 mol%. Independent longitudinal modulus (CL), shear modulus (mu) and bulk modulus (K-e) showed similar behaviors to both velocities. Hardness (H), Debye temperature (theta(D)) and glass transition temperature (T-g) also substantially increased for x = 10 mol% before reaching a saddle-like behaviorbetween 10 and 15 mol% Fe2O3. Subsequently, a slight increase at x> 15 mol% was observed. The anomalous region between 10 mol% <= x <= 15 mol% coincided with DC conductivity saddle-like region and is suggested to be related to the mixed transition-ion effect (MTE). Meanwhile, in same region, optical band gap (E-opt) exhibited a maxima, whereas refractive index showed a minima, thereby indicating a variation in polarizability due to the changes in concentration of bridging and non-bridging oxygens.