Synthesis of Al³⁺-Substituted La M-Type Hexaferrite for In Situ Ceramic Composite Processing

Abstract

La(Fe, Al)₁₂O₁₉ powder was synthesized by the two-step solid-state reaction of La(Fe, Al)O₃ with α-Fe₂O₃ and α-Al₂O₃ powders. The stability and the formation rate of LaFe₁₂O₁₉-based magnetoplumbite compounds are greatly improved by the formation of a solid solution with La_xAl₁₂O₁₉. The highest value of the saturation magnetization (52.9emu/g) was obtained at the composition of 95mol% LaFe₁₂O₁₉ (LaM95) in La(Fe, Al)₁₂O₁₉. In Ce-TZP (ceria-stabilized tetragonal zirconia polycrystal) ceramic matrix, 90mol% LaFe₁₂O₁₉ in La(Fe, Al)₁₂O₁₉ (LaM90) was stable in a wider temperature range than LaM95. Platelike LaM90 crystals were successfully grown in situ in Ce-TZP matrix at temperatures ranging from 1350 to 1375°C. The formation of anisotropic La(Fe, Al)₁₂O₁₉ crystals was found to depend upon the preferential diffusion of La³⁺ ions through the initially formed magnetoplumbite lattice.