Polarons in boron doped iron phosphate glasses

The electrical conductivity and dielectric properties of xB2O3–(40−x)Fe2O3–60P2O5 (x=6–20, mol%) glasses were investigated in the frequency range from 0.01 Hz to 1 MHz and the temperature range from 303 K to 523 K. At temperatures below 523 K an ac conductivity and the dielectric constant follow the universal dielectric response (UDR), being typical for hopping or tunneling of localized charge carriers. A detailed analysis of the temperature dependence of the UDR parameter s in terms of the theoretical model for tunneling of small polarons revealed that below523 K thismechanismgoverns the charge transport in these glasses. The comparison of the values of characteristic coefficientsW∞ and α determined by two different methods confirms the polaronic behavior of boron doped iron phosphate glasses.