Thermally activated polaron tunnelling conduction mechanism in Sr <sub>2</sub> MnO <sub>4</sub> synthesized by quenching in ambient atmosphere
Gurudeo Nirala, Dharmendra Yadav, Shail Upadhyay
Abstract
Abstract The oxide Sr 2 MnO 4 was synthesized using the solid-state reaction technique. Quenching in air from 1500 °C to room temperature yielded the pure phase powder of Sr 2 MnO 4 . 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 Mn 3+ and Mn 4+ 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.