Effect of K doping on Mo⁶⁺stability and ionic conductivity study in La₂Mo₂O₉ as oxide-ion conductor

The structural stability and ionic conductivity of K doped LAMOX have been extensively studied by many researchers. But the chemical state analysis and relaxation dispersion studies of La1.9K0.1Mo2O9−δ, La1.8K0.2Mo2O9−δ and pristine La2Mo2O9 are very scarcely reported. Here in the present study, the chemical state analysis, relaxation dispersion along with structural stability and ionic conductivity studies are done to investigate the effect of K doping in LAMOX. The room temperature XRD analysis of La1.9K0.1Mo2O9−δ, La1.8K0.2Mo2O9−δ compounds shows formation of β-LAMOX phase along with K2O as an additional phase. The x-ray photoelectron spectroscopy (XPS) results are analysed for both K doped compositions sintered in air as well as in Ar 90%–H2 10% atmosphere. Both the compositions show good amount of Mo6+ stabilisation in Ar–H2 atmosphere. The Raman spectroscopy analysis of La1.9K0.1Mo2O9−δ and La2Mo2O9 shows the signature of oxygen vacancies at 866 cm−1. The activation energy (Ea) is found to be 0.66 eV for La1.8K0.2Mo2O9−δ. The low value of d.c. conductivity of 12 μS cm−1 at 400 °C may be due to the hindrance imposed by large ionic radius of K+ ion as compared to La3+ ion in the structure which restricts its applications in IT-SOFCs.