Study of polaron transport mechanisms in two transition metal ions doped borophosphate glasses

Resumo

Borophosphate glasses in the compositions, (B₂O₃)_0.2 · (P₂O₅)_0.3 · (V₂O₅)_x · (CoO)_0.5x, where x = 0.05, 0.1, 0.15, 0.20, 0.25, 0.30, 0.35, 0.40, 0.45, 0.50 were synthesized at 1500 K by standard melt quenching method. Non-crystalline nature of the samples was confirmed by XRD studies. Room temperature density and dc electrical conductivity in the temperature range from 350 K to 625 K have been measured. Density decreased up to about 0.25 mole fractions of V₂O₅ and increased thereafter. Conductivity was almost constant up to 0.25 mole fractions of V₂O₅ and increased for higher amount of V₂O₅. Temperature variation of conductivity data has been analyzed using Mott’s small polaron hopping (SPH) model and, activation energy and Debye’s temperature were determined. Activation energy decreased with increase of V₂O₅ content. The data deviated from the Mott’s SPH model has been analyzed in view of variable range hopping models of Mott and Greaves and the density of states at Fermi level was determined. It is for the first time that borophosphate glasses doped with V₂O₅ and CoO were synthesized to study conductivity variation with temperature. The data analyzed using small polaron hopping and variable range hopping models.