Thermally activated polaron tunnelling conduction mechanism in Sr₂MnO₄ synthesized by quenching in ambient atmosphere

Abstract

The oxide Sr2MnO4 was synthesized using the solid-state reaction technique. Quenching in air from 1500 °C to room temperature yielded the pure phase powder of Sr2MnO4. The purity of synthesized powder was further examined by FTIR analysis. The Rietveld refinement of XRD data confirmed the tetragonal structure and I4/mmm space group. The band gap, computed from the Tauc’s plot, was found to be 1.15 eV. The XPS analysis depicted the presence of Mn3+ and Mn4+ valence states. Measurement of the AC electrical conductivity over wide temperature (30 °C–500 °C) and frequency (0.020–2 MHz) ranges were carried out. The conduction mechanism changed from small polaron tunnelling (<270 °C) to non-overlapping large polaron tunnelling (>270 °C). The frequency versus imaginary part of the impedance (Z″) and modulus (M″) plots exhibited a change in the conduction domain with increase in temperature. This result was further verified by the Ghosh’s scaling of the conductivity spectra.