Crystal Chemistry and Phase Equilibria Studies of the BaO-R2O3-CuO Systems. II: X-Ray Characterization and Standard Patterns of BaR2O4, R = Lanthanides

AbstractThe compounds BaR2O4, where R = La, Nd, Sm, Gd, Eu, Dy, Ho and Er have been prepared from a stoichiometric mixture of BaCO3and lanthanide oxides, and characterized by X-ray powder diffraction. Standard X-ray patterns of these phases were prepared. In general, BaR2O4crystallizes in the pervoskite-related CaFe2O4structure which is orthorhombic with a space group Pnam. The cell parameters of these compounds from R = Er to La range from 10.3729(12) to 10.668(2) ? for a, 12.0699(11) to 12.642(2) ? for b, from 3.4356(4) to 3.7037(10) ? for c, and from 450.14(5) ?3to 499.51 ?3for V respectively. A monotonic, linear relationship is obtained when V is plotted against the cube of the ionic radius of R. When R = Tm, Lu and Yb, the BaO?R2O3composition produced the mixture Ba3R4O9and the unreacted lanthanide oxide. Under the present experimental conditions, the compound BaRO3was the predominant component when R = Ce, Pr, and Tb.