Oxygen deficient perovskite (SrMnO 32d ) is formed by direct precursor (SrCO 3 /Mn 2 O 3 ) reaction in air at 1100uC. X-ray diffraction (XRD) results confirmed single phase polycrystalline ceramic having layered hexagonal crystal structure [lattice parameters a55?437(7) A ˚, c59?073(7) A ˚]. Fourier transform infrared results support perovskite phase. Field emission scanning electron microscopy reveals dense polycrystalline (1-9 mm) 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 d y0?12 under thermally activated condition with T>1065uC. 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 700uC when compared with ambient conductivity y10 28 . Activation energy (y1?0 eV) suggests intergranular activity due to O 22 ion migration via diffusion through lattice vacancy.

No abstract

No abstract