Insight into charge conduction and relaxation in La2-xCaxFeMnO6 solid solution double perovskites

A series of La_2-xCa_xFeMnO₆ (where x = 0, 0.1, 0.2, and 0.5) solid solution has been prepared by the solid-state reaction method. Single-phase disordered cubic crystal structure of crystallite size ~ 50 nm has been confirmed by the Rietveld refinement of X-ray diffraction (XRD) data. Raman spectroscopic study shows improper disordering of MnO₆ and FeO₆ octahedral. The average grain size (~ 4 µm) and elemental analysis have been estimated by SEM and EDS measurements, respectively. The electronic structure of the prepared samples has been investigated by using the X-ray photoemission spectroscopy (XPS). The value of dielectric constant has been improved from colossal (~1826) to giant (~15238) with low dielectric loss at room temperature due to Ca²⁺ doping. All samples exhibit the negative temperature coefficient of resistance (NTCR) characteristic. The electrical characteristics of both the grain and grain boundary have been investigated by the analysis of imaginary part of impedance (Z''). The non-Debye type relaxation has been explained by the non-overlapping small polaron tunnelling (NSPT) transport mechanism. I-V characteristic shows the low value of leakage current density (~ 10^-4 Amp/cm²) for all measured samples. This study may open an intriguing path for the engineering of better-performing dielectric materials for various electronic devices.