Impedance behaviors of Nd-doped BiFeO 3 ceramics with 0.10 ≤ x ≤ 0.30

The Bi 1- x Nd x FeO 3 (BNFO) ceramics with 0.10 ≤ x ≤ 0.30 were fabricated by the solid-state reaction method. As Nd concentration x increases, the samples experience a structural phase transition from R3c phase to Pnma phase with the intermediate phase Pna2 1 . The systematical study on the impedance spectra that are plotted with various formalisms reveals that the grain effect dominates the single non-Debye thermally activated relaxation process, and an equivalent parallel circuit with RC element and constant phase element can interpret the impedance Nyquist plots for all the samples with a good fitting result. The frequency-dependent normalized impedance and modulus spectra and the ac conductivity analysis suggest the primary role of the localized conductivity in the BNFO system, which may be possibly assisted by small polarons and affected by the structural phase transition in the sample. According to the estimated values of activation energy E_a derived from temperature-dependent dc conductivity data, it is speculated that the doubly ionized oxygen vacancies combined with ferroelectric interactions may be responsible for the short-range movements in the conductivity and relaxation process.