Phase Equilibria, Oxygen Content and Properties of Oxides in the ½ Dy ₂ O ₃ –BaO–½ Fe ₂ O ₃ System

Systematic study of phase equilibria in the ½ Dy 2 O 3 –BaO–½ Fe 2 O 3 system at 1100°C in air reveals the formation of the following complex oxides: Dy 1.05 Ba 1.95 Fe 3 O 8+ w (SG P4/mmm ), Ba 3 DyFe 2 O 7.5+γ (SG Pnam ), Dy 0.9 Ba 0.9 FeO 4‐β (SG Pnma ), and BaFe 1‐ y Dy y O 3‐δ ( y = 0 − 0.15, SG Pm ‐ 3m ). It is shown that Ba 3 DyFe 2 O 7.5+ γ , which has an orthorhombic structure at 1100°C, transforms into a monoclinic structure near 700°C. Examination of the quasi‐binary ½ Dy 2 O 3 –BaO constituent system exhibits the existence of Dy 4 Ba 3 O 9 , which is unstable at lower temperatures, and Dy 1.95 Ba 1.05 O 4 , whose stoichiometry in metallic components is shifted from the ideal one, reported previously as “Dy 2 BaO 4 ”. The phase diagram for the ½ Dy 2 O 3 –BaO–½ Fe 2 O 3 system at 1100°C in air consists of 16 phase fields. Oxygen‐deficient solid solutions BaFe 1‐ y Dy y O 3‐ δ and over‐stoichiometric Ba 3 DyFe 2 O 7.5+ γ begin to lose oxygen at 400°C. In contrast, the oxygen content in both Dy 1.05 Ba 1.95 Fe 3 O 8+ w and Dy 0.9 Ba 0.9 FeO 4‐ β remains almost unchanged over the entire temperature range. The shape of the temperature dependences of thermal expansion, as well as electrical conductivity and the Seebeck coefficient, correlates well with changes in the oxygen content for all oxides and structural transformation of Ba 3 DyFe 2 O 7.5+ γ .