Impedance Spectroscopy Properties of Pr0.67A0.33MnO3 (A = Ba or Sr) Perovskites

We have investigated the dielectric properties of Pr 0.67 Ba 0.33 MnO 3 (PBMO) and Pr 0.67 Sr 0.33 MnO 3 (PSMO) perovskites synthesized by the solid-state reaction method at 1473 K. Samples were characterized by complex impedance spectroscopy (CIS) in the frequency range from 40 Hz to 1 MHz, at room temperature. The conductivity curves for the two samples were well fitted by the Jonscher law σ ( ω )= σ dc + Aω n . For the PBMO sample, the hopping process occurs at long distance, whereas for PSMO compound it occurs between neighboring sites. Frequency dependence of dielectric constant ( ε ″) and tangent loss (tan δ ) show a dispersive behavior at low frequencies that was explained on the basis of the Maxwell–Wagner model and Koop’s theory. Electric modulus formalism has been employed to study the relaxation dynamics of charge carriers. For both compounds, the variation of the imaginary part Z ″ shows a peak at a relaxation angular frequency ( ω r ) related to the relaxation time ( τ ) by τ =1/ ω r . Nyquist plots of impedance show the presence of two semicircles and an electrical equivalent circuit has been proposed to explain the impedance results.