Studies on structural and electrical properties of SrMnO _{3− δ} prepared in oxidising medium

Oxygen deficient perovskite (SrMnO3−δ ) is formed by direct precursor (SrCO3/Mn2O3) reaction in air at 1100°C. X-ray diffraction (XRD) results confirmed single phase polycrystalline ceramic having layered hexagonal crystal structure [lattice parameters a = 5·437(7) Å, c = 9·073(7) Å]. Fourier transform infrared results support perovskite phase. Field emission scanning electron microscopy reveals dense polycrystalline (1-9 μm) microstructure and TEM/SAED pattern exhibits excellent correlation with the hexagonal structure in good agreement with XRD results. Thermal analysis in oxygen medium indicated intrinsic oxygen non-stoichiometry in the sample with δ ∼0·12 under thermally activated condition with T1065°C. Complex impedance spectroscopy (CIS) results on electrical properties confirmed both the bulk (grain) and grain boundary contribution in different temperature ranges. An equivalent electrical circuit model using CIS response suggests cascading of parallel resistance-capacitance (‘RC’) combination in agreement with ‘brick layer model’. Direct current conductivity obeys thermally activated Arrhenius behaviour. Substantial conductivity enhancement (about five orders) occurs at 700°C when compared with ambient conductivity ∼10−8. Activation energy (∼1·0 eV) suggests intergranular activity due to O2− ion migration via diffusion through lattice vacancy.