Structure, oxygen stoichiometry and electrical conductivity of LnPrO3+y (Ln=Y and Lanthanide) oxides

The crystal structure and d.c. electrical conductivity of a series of homogeneous mixed rare-earth oxides in LnPrO3+y (Ln=Y and lanthanide ion) system are reported. It is found that the ionic size of Ln determines the crystal structure of the oxides in this series. LaPrO3+y and CePrO3+y crystallise in the fluorite structure(fcc), whereas the remaining oxides adopt the C-type rare-earth oxide structure. The electrical conductivity measurements show that conductivity is structure type dependent with the fluorites (wherein Ln=La) having a lower conductivity than the C-type mixed oxides (wherein Ln=Gd, Sm, Ho, Er and Y). The conductivity of the mixed oxides at 1020 K, is of the order of 10−2 Ω−1 cm−1 which is about five orders of magnitude higher compared to their room temperature conductivity. Oxygen excess in these compositions has been determined from wet-chemical analysis and temperature programmed oxygen evolution studies. The mixed oxides evolve oxygen in two distinct stages and the conductivity–temperature plot shows discontinuities corresponding to the onset of oxygen evolution.