Phosphorus-substitution effect on the phase stabilization, electrical and spectroscopic properties of LAMOX-based...

A series of P⁵⁺ - doped La₂Mo₂O₉ phases with different concentrations of P⁵⁺ were prepared using conventional solid-state reactions. The formation of phase-pure P⁵⁺-doped La₂Mo₂O₉ has been monitored by powder X-ray diffraction, thermal analysis, conductivity measurements, Raman, and FT-IR absorption techniques. The structure and lattice parameters of La₂Mo_2-PO_9- are obtained from Rietveld refinement. The effect of substituting P for Mo reveals that the phase transition which occurs in La₂Mo₂O₉ around 560 °C disappears when y > 0.02, as demonstrated by thermal analysis. Pure P⁵⁺-doped phases with monoclinic structure (α-form, the space group P2₁) were observed for the concentration of optically active ions up to y = 0.02. When the concentration of P⁵⁺ ions is higher, a cubic structure (β-form, the space group P2₁3) starts to appear. However, up to the concentration of y = 0.03 of the P⁵⁺ 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.