Structure, oxygen stoichiometry and electrical conductivity of LnPrO(3+y) (Ln = Y and Lanthanide) oxides

The crystal structure and d.c. electrical conductivity of a series of homog eneous mixed rare-earth oxides in LnPrO(3+y) (Ln = Y and lanthanide ion) sy stem are reported. It is found that the ionic size of Ln determines the cry stal structure of the oxides in this series. LaPrO3+y and CePrO3+y crystall ise 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 (whe rein Ln = La) having a lower conductivity than the C-type mixed oxides (whe rein Ln = Gd, Sm, Ho, Er and Y). The conductivity of the mixed oxides at 10 20 K, is of the order of 10(-2) Ohm(-1) cm(-1) which is about five orders o f 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 evol ve oxygen in two distinct stages and the conductivity-temperature plot show s discontinuities corresponding to the onset of oxygen evolution. (C) 1999 Elsevier Science S.A. All rights reserved.