Change of Mott variable range to small polaronic hole hopping conduction mechanism and formation of Schottky barriers in Nd0.9Sr0.1FeO3

Abstract

In this work, single phase Nd0.9Sr0.1FeO3 electroceramic material has been synthesized by solid state reaction method. Phase purity and microstructure were analyzed by X-ray diffraction and SEM. By employing impedance spectroscopy, ac electrical properties have been measured in wide temperature (77–358 K) and frequency (1–1.5 × 107 Hz) range. To correlate the electrical properties an equivalent circuit (RgQg)(RgbQgb)(RcQc) has been used at lower temperatures which gradually changed to (Rgb)(RcQc) at higher temperatures. Around 218 K, the conduction mechanism changed from variable range hole hopping to small polaronic hole hopping mechanism which was also confirmed by ac conductivity and magnetization measurements. The localization length calculated for grains and grain boundaries are 1.17 Å and 1.06 Å, respectively. Hall measurements pointed out that majority of the charge carriers are p-type. The dc bias measurements confirmed the presence of non-ohmic electrode contacts and obeyed the Mott-Schottky law. The observed permittivity of grains is from 8 to 10, whereas the high permittivity at elevated temperatures may be due to the formation of different Schottky barriers, as a result of ceramic interfaces, ceramic surfaces, and electrode effects.