Effect of Na ₂ O Additions in the Crystallization of Barium Ferrite from a BaO‐B ₂ O ₃ ‐Fe ₂ O ₃ Glass

Abstract

A glass crystallization method was utilized to synthesize nanosized BaO‐6Fe 2 O 3 platelets from a 0.412BaO‐0.258B 2 O 3 ‐0.330Fe 2 O 3 batch composition. Quenched ribbons were inhomogeneous, showing microclustering and ∼1 μm hematite crystals. Na 2 O substitutions for BaO greatly enhanced the glass‐forming tendency of quenched ribbons, though quenched‐in ∼0.5 μm barium ferrite crystals were infrequently present. The improved homogeneity with Na 2 O substitution was attributed to lower vapor pressure of BaO during batch melting, which increased its retention in the as‐quenched ribbons. Quantities of BaO equal to or in excess of Fe 2 O 3 allowed iron ions to adopt stable network positions in the glass melt. With Na 2 O substitution, devitrification of dispersed ∼40 nm barium ferrite particles from phase‐separated regions occurred after secondary heat treatment. 5 mol% Na 2 O batch substitution showed the lowest crystallinity in the as‐quenched ribbons, and the highest crystallinity after secondary heat treatment. After optimum devitrification, the maximum values of saturation magnetization and coercivity were 21.22 emu/g and 2.82 kOe, respectively.