Conductivity relaxations and phase purity in strontium cobalt oxides prepared by numerous chemical routes

Strontium cobalt oxide (SrCoO3-δ) nanoparticles were successfully synthesized using; composite mediated hydrothermal (CMHM), without water and surfactants (WOWS) sol-gel and co-precipitation methods. The probable electrical conduction mechanism of synthesized strontium cobaltite was investigated via complex impedance analysis. Characterization techniques were employed to study the dependence of structure, homogeneity, physical parameters and electrical properties on synthesis procedures. After heat treatment, X-Ray Diffraction (XRD) confirmed the formation of phase pure SrCoO3-δ powders synthesized with CMHM, WOWS sol-gel and co-precipitation methods. Fourier Transform Infrared Spectroscopy (FTIR) spectra indicated the presence of fingerprint region of perovskite (ABO3-δ) structure. Raman spectroscopy revealed the internal motion of oxygen inside the CoO6 octahedra of SrCoO3-δ perovskite structure. A Raman phonon mode under 600 cm−1 position was identified which is commonly observed for such perovskite oxide. Scanning Electron Microscopy (SEM) images showed uniformly diffused, microporous and agglomerated sphere like morphology. Differential Thermal Analysis (DTA) and Thermogravimetry (TGA) verified formation of intermediate metal carbonates that decomposed to final product. Complex impedance spectroscopic plots (Nyquist plots) against frequency (20 Hz–3 MHz) discovered single semi-circular arcs in the low frequency region. These arcs showed that, grain boundary contribution is dominated over grain contribution to the total electrical conduction behavior. Modulus analysis disclosed non-Debye type conductivity relaxation in hydrothermally synthesized samples. The AC conductivity graphs followed Jonscher's power law and hopping model. Hydrothermally synthesized samples exhibited minimum impedances and maximum AC conductivity, which makes them excellent candidate for cathode material in intermediate temperature range solid oxide fuel cells (IT-SOFCs) applications.