The ac impedance and conductivity properties of Dy doped Bi 4 V 2 -x Dy x O 11 (x = 0.05, 0.10, 0.15 and 0.20) ceramics prepared by solid-state reaction technique, in a wide frequency range at different temperatures have been studied. All the samples exhibited b-type phase orthorhombic structure at room temperature. The Nyquist plot confirmed the presence of both grain and grain boundary effects for all Dy doped samples. Double relaxation behavior was also observed. The grain and grain boundary resistance decreases with rise in temperature for all the concentration and exhibits a typical negative temperature co-efficient of resistance (NTCR) behavior. An analysis of the electric modulus suggests the possible hopping mechanism for electrical transport processes of all the materials. The ac conductivity spectrum obeys Jonscher's universal power law. DC conductivity of the materials were also studied and values of the activation energy found to be 0.40, 0.49, 0.73 and 0.78 eV for the compositions x = 0.05, 0.10, 0.15 and 0.20, respectively, at different temperatures (150-375°C).

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Rare earth (Nd) doped polycrystalline samples, Bi4V2-xNdxO11 (x = 0.05, 0.10, 0.15 and 0.20), were prepared by using solid–state reaction technique. The physical properties of the samples were studied by X-ray diffraction, FT-IR spectroscopy, scanning electron microscopy (SEM) and AC impedance. The studied samples showed an orthorhombic structure for x = 0.05–0.10 and monoclinic structure for x = 0.15–0.20 through X-ray diffraction (XRD) at room temperature. The nature of Nyquist plot confirmed the presence of contribution of both grain and grain boundary effects and non-Debye type of relaxation process occur for all Nd doped compounds. The frequency dependent ac conductivity followed Jonscher's universal power law. Dimensionless frequency exponent (n) and dispersion parameter (A) were determined by fitting the power law. The nature of variation of dc conductivity suggested the Arrhenius type of electrical conductivity for all the samples. The activation energies were found to be increased with increase in Nd content on vanadium site. The value of dc conductivity is high (0.78 eV) for x = 0.20.