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

• Lithium bismo-borate glasses with different NiO and V2O5 content are prepared.
• Glass structure expands with increase in (2NiO ∙ V2O5) content.
• Synthesized glasses exhibit standard dielectric behavior.
• Equivalent circuit is analyzed as parallel combination of Rb and CPE.
• VO2 +-ion has octahedron symmetry with tetragonal compression.

Glasses having composition 7NiO ∙ 23Li2O ∙ 20Bi2O3 ∙ 50B2O3, 7V2O5 ∙ 23Li2O ∙ 20Bi2O3 ∙ 50B2O3 and x(2NiO ∙ V2O5) ∙ (30 − x)Li2O ∙ 50B2O3 ∙ 20Bi2O3 (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 ∙ V2O5 in the base glass matrix. Different dielectric parameters viz. dielectric loss (ε), electrical modulus (M), loss tangent (tanδ) 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 (Rb) 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.

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