Phase relations and thermodynamic properties of compounds in the pseudobinary system BaO-Y₂O₃

Abstract

The coexisting phases in the pseudobinary system BaO-Y₂O₃ have been identified by equilibrating samples containing different amounts of component oxides at 1173, 1273 and 1373 K. Only two ternary oxides, BaY₂O₄ and Ba₃Y₄O₉, have been found to be stable in the temperature range of investigation. Solid state galvanic cells: Pt, O₂+BaO+BaF₂||BaF₂+2mol%Al₂O₃||BaF₂+BaY₂O₄+Y₂O₃+O₂, Pt and Pt, O₂+BaO+BaF₂||BaF₂+2mol% Al₂O₃BaF₂+BaY₂O₄+Ba₃Y₄O₉+O₂, Pt have been employed for determining the Gibbs' energies of formation of BaY₂O₄ and Ba₃Y₄O₉ from the component oxides in the range 850 to 1250 K. A composite solid electrolyte incorporating Al₂O₃-dispersed BaF₂ was used in the cells. To prevent interaction between the Al₂O₃ powder and electrode materials, the solid electrolyte was coated with pure BaF₂. The Gibbs' energies of formation of BaY₂O₄ and Ba₃Y₄O₉ from component oxides are given by: Δ_f⁰ (BaY₂O₄, s)=-128,310+5.211T (±580) J mol^-1, (850≤T≤1250 K) and Δ_f^o(Ba₃Y₄O₉, s)= -317,490 -24.704T (±1100) J mol^-1, (850≤T≤1250 K).