Mixed conduction in Alkali and transition metal ion doped borate glasses

A series of borate glasses of composition (B2O3)0.5, (Na2CO3)0.05-x, (Fe2O3) x where, x = 0.05, 0.1, 0.15, 0.2, and 0.25 have been synthesized by melt quench technique. The samples were annealed and their non-crystallinity confirmed by X-ray diffraction studies. The room temperature density was measured. The DC conductivity measurement were carried out for temperature range from 323K to 573K. The high temperature activation energy has been determined using Mott's small polaron hopping model and density of states were determined using variable range hopping models. The activation energy, conductivity and various polaron related parameters were compared with literature. The change in conductivity and activation energy with composition indicated changeover of predominant conduction mechanism form ionic to electronic for 0.2 mole fractions of Fe2O3. Mayer-Neldel's rule also confirmed for the first time that the changeover of predominant conduction mechanism in borate glasses doped with Na and Fe ions.