Synthesis and characterization of Er doped La2Mo2O9 oxide ion conductors: the influence of isovalent doping

Tanmoy Paul, Department of Chemical Engineering, Technion Israel Institute of Technology, Haifa, Israel
Yoed Tsur, Department Of Chemical Engineering, Technion Israel Institute Of Technology, Haifa, Israel

For solid oxide fuel cell oxide ion conductors are very important. Currently, the most commonly used oxide ion conductors are zirconia based and ceria based. However, La₂Mo₂O₉ is found to be most efficient oxide ion conductor that provide similar oxide ion conductivity (10^-2 S cm^-1) with that of YSZ at 800 ⁰C. In this work, we try to monitor the effect of isovalent doping of Er on La site structurally and measuring conductivity by X-ray and impedance spectroscopy respectively. The crystal symmetry was determined without performing rigorous Rietveld refinement of X-ray data just by scanning a low angle θ-2θ Bragg position. The structures of the Er doped La₂Mo₂O₉ compounds were found to be cubic. The impedance spectra were analyzed by impedance spectroscopy genetic programming method up to 600 ⁰C. Using this MATLAB based program a distribution function of relaxation times (DFRT) was determined which was found to be temperature and composition sensitive. Two distinguishable peaks in each DFRTs correspond to grain and grain boundary. The activation energies for both grain and grain boundary are obtained to be ~ 1.11 ± 0.01 eV and 1.20 ± 0.05 eV respectively. Despite the fact that Er is an isovalent dopant, the oxide ion conductivity is found to be composition dependent. It is observed that decrease in grain boundary conductivity increases the space charge potential at the grain boundary.

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   T. Paul and Y. Tsur, Solid State Ionics 323, 37 (2018).