Evolution of Jahn–Teller distortion, transport and dielectric properties with doping in perovskite NdFe1−xMnxO3 (0 ≤ x ≤ 1) compounds
We have carried out dielectric and transport measurements in NdFe1−xMnxO3 (0 ≤ x ≤ 1) series of compounds and studied the variation of activation energy due to a change in Mn concentration. Despite similar ionic radii in Mn3+ and Fe3+, large variation is observed in the lattice parameters and a crossover from dynamic to static Jahn–Teller distortion is discernible. The Fe/Mn–O–Fe/Mn bond angle on the ab plane shows an anomalous change with doping. With an increase in the Mn content, the bond angle decreases until x = 0.6; beyond this, it starts rising until x = 0.8 and again falls after that. A similar trend is observed in activation energies estimated from both transport and dielectric relaxation by assuming a small polaron hopping (SPH) model. Impedance spectroscopy measurements delineate grain and grain boundary contributions separately both of which follow the SPH model. Frequency variation of the dielectric constant is in agreement with the modified Debye law from which relaxation dispersion is estimated.