Impedance and Electric Modulus Spectroscopy of Polycrystalline La0.5Sr0.5Bi0.2Co0.4Fe0.4O3-δ Cathode Ceramic for Intermediate Temperature SOFCs.

In the present research work, La_0.5Sr_0.5Bi_0.2Co_0.4Fe_0.4O_3-δ cathode ceramic powder is synthesized through cost-effective flash pyrolysis process and followed by conventional sintering for IT-SOFCs. The Rietveld refinement program is used to determine the crystal structure, unit cell parameters and bond length. The XRD result indicates existence of a pure single phase of rhombohedral structure with R3 °C space group symmetry detected from the sample sintered at 700 °C. FESEM micrographs of fracture surface of sample sintered at 700 °C showed a high porosity and nano grain sizes (50-100 nm). Combined impedance and electric modulus spectroscopic are used to investigate the relaxation phenomena in La_0.5Sr_0.5Bi_0.2Co_0.4Fe_0.4O_3-δ ceramic over a broad range of temperature and frequency. A single relaxation peak is observed in the imaginary part of impedance and electric modulus spectra, which could be due to the contribution of grain boundary of La_0.5Sr_0.5Bi_0.2Co_0.4Fe_0.4O_3-δ ceramic. The imaginary part of modulus (M") spectra is studied with help of non-exponential decay function or Kohlrausch-Williams-Watts (KWW) parameter (ß). In the combined plot of the imaginary part of impedance (Z") and electric modulus (M") spectra at 210 °C, only a single peak of Z" and M" is observed at the same frequency which specifies that the conduction process is a long-range motion of the charge carriers. The frequencydependent conductivity is followed by the Jonscher's double power law in the temperature range 30-210 °C. [ABSTRACT FROM AUTHOR]