Effect of Cu2+ substitution on structural, electrical and dielectric properties of bismuth vanadate by impedance spectroscopic studies

Polycrystalline samples of Bi₄V_2(1-x)Cu_2xO_11-3× were prepared by solid state reaction method. Thrust of the work is to stabilize high temperature conducting γ-phase at room temperature. XRD and DSC analysis indicates orthorhombic ‘α’ phase for x ≤ 0.08 to tetragonal γ-phase transition for x = 0.1, at room temperature. Variations of real and imaginary impedance as well as complex electrical modulus with frequency are reported. Experimental impedance spectroscopic data was theoretically fitted and equivalent circuits are proposed. Nyquist plots revealed contribution from grain as well as interface. Variations of impedance, dielectric permittivity and AC conductivity as a function of frequency at selected temperatures are reported. The AC conductivity was fitted with Jonscher’s power law and the power law exponent (η) was found to be < 1, indicating that the conduction process follows CBH mechanism. The dielectric behaviour was found to follow UDR model. Cu²⁺ ions was observed to introduce defects and oxygen vacancies, space charge accumulation, reduction in dielectric permittivity and increase in the conductivity as high as up to 0.45 S·cm⁻¹ for the expected γ-phase.