EPR and impedance spectroscopic investigations on lithium bismuth borate glasses containing nickel and vanadium ions

Glasses having composition 7NiO center dot 23Li(2)O center dot 20Bi(2)O(3)center dot 50B(2)O(3), 7V(2)O(3)center dot 23Li(2)O center dot 20Bi(2)O(3)center dot 50B(2)O(3) and x(2NiO center dot V2O5)center dot(30-x)Li-20 center dot 50B(2)O(3)center dot 20Bi(2)O(3) (with x = 0, 2, 5, 7 & 10 mol%) prepared through melt-quench route are explored by analyzing density, impedance spectroscopy and electron paramagnetic resonance (EPR). It is found that both density and molar volume increase with an increase in substitution of 2NiO center dot V2O5 in the base glass matrix. Different dielectric parameters viz. dielectric loss (epsilon), electrical modulus (M), loss tangent (ran delta) etc. are evaluated and their variations with frequency and temperature are analyzed which reveals that these glasses exhibit a non-Debye relaxation behavior. A phenomenal description of the capacitive behavior is obtained by considering the circuitry as a parallel combination of bulk resistance (R-b) and constant phase element (CPE). The conduction mechanism is found to follow Quantum Mechanical Tunneling (QMT) model. Spin Hamiltonian Parameters (SHPs) and covalency rates are calculated from the EPR spectra of vanadyl ion. The observed EPR spectra confirmed that V4+ ion exists as vanadyl ion in the octahedral coordination with tetragonal compression. (C) 2015 Elsevier B.V. All rights reserved.