Phosphorus-substitution effect on the phase stabilization, electrical and spectroscopic properties of LAMOX-based electrolyte for solid oxide fuel cells.

A series of P - doped LaMoO phases with different concentrations of P were prepared using conventional solid-state reactions. The formation of phase-pure P-doped LaMoO has been monitored by powder X-ray diffraction, thermal analysis, conductivity measurements, Raman, and FT-IR absorption techniques. The structure and lattice parameters of LaMoPO are obtained from Rietveld refinement. The effect of substituting P for Mo reveals that the phase transition which occurs in LaMoO around 560 °C disappears when > 0.02, as demonstrated by thermal analysis. Pure P-doped phases with monoclinic structure (α-form, the space group 2) were observed for the concentration of optically active ions up to = 0.02. When the concentration of P ions is higher, a cubic structure (β-form, the space group 23) starts to appear. However, up to the concentration of = 0.03 of the P ion a mixture of the monoclinic and cubic phases has been observed. From infrared and Raman analysis it is confirmed that different vibration modes arise from the vibration of molybdenum-oxygen bands. Mo-O bond lengths are also found to be independent of P-doping.