Magnetic Dielectric Oxides: Subsolidus Phase Relations in the BaO:Fe2O3:TiO2System

Abstract

The BaO–Fe2O3–TiO2ternary phase diagram has been investigated at 1250–1270°C in air. X-ray diffraction studies of approximately 150 polycrystalline specimens at room temperature confirmed the existence of sixteen ternary compounds. Two of these compounds, BaFe4Ti2O11and Ba12Fe28Ti15O84, were previously reported, four were found to be isostructural with known chemically similar compounds, and ten apparently adopt new structure-types. The crystal structures of five of the new ternary phases are briefly described. The oxidation state of iron found in this study is similar to that reported for a study of the BaO–Fe2O3–SnO2system in air at 1200°C. No indications of reduction of Fe3+of Fe2+were observed; however, oxidation to Fe4+was clearly indicated in an extensive solid solution BaTi1−xFexO3−z,x= 0.06 → 0.84, with the hexagonal BaTiO3structure. Substantial solid solution regions were also found for the hollandite-type structure (BaxFe2xTi8−2xO16,x= 1.07 → 1.33), and for TiO2dissolved in the BaFe12O19structure (end member BaFe10.8Ti0.9O19). The complexity of the BaO–Fe2O3–TiO2system is attributed to the coordinative versatility of Fe3+in a close-packed O/Ba–O matrix and the resulting opportunity to form a wide variety of layered structures with different stacking sequences and distortions from ideal packing.