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

Abstract

In the present research work, La 0.5 Sr 0.5 Bi 0.2 Co 0 . 4 Fe 0.4 O 3– d cathode ceramic powder is synthesized through cost-effective flash pyrolysis process and further conventional heat treatment for sintering for IT-SOFCs. The crystal structure, unit cell parameters and bond length are determined by using the Rietveld refinement program. The XRD result indicates existence of a pure single phase with R C space group symmetry detected from the sample which has been sintered at 700 ℃. SEM images of fracture surface of sample sintered at 700 ℃ showed a high porosity and nano grain sizes (50-100 nm). Impedance and electric modulus spectroscopic methods are used to identify the relaxation phenomena in La 0.5 Sr 0.5 Bi 0.2 Co 0 . 4 Fe 0.4 O 3– d 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 0.5 Sr 0.5 Bi 0.2 Co 0 . 4 Fe 0.4 O 3– d ceramic. The imaginary part of modulus ( ) spectra is analyzed with help of non-exponential decay function or Kohlrausch–Williams–Watts (KWW) parameter ( β ). In the combined plot of the imaginary part of impedance and electric modulus spectra at 210 ℃, only a single peak of and is observed at the same frequency which indicates that the conduction process is a long-range motion of the charge carriers. The frequency-dependent conductivity is followed by the Jonscher’s double power law in the temperature range 30-210 ℃.