Submicron Barium Hexaferrite Ceramics Manufactured by Low-Temperature Liquid-Phase Sintering of BaFe₁₂O₁₉ Nanoparticles

This work has solved the problem of manufacturing high-coercivity barium hexaferrite BaFe₁₂O₁₉ ceramic samples. A BaFe₁₂O₁₉ nanopowder with coercivity H_c = 445 kA/m was prepared by hydrothermal synthesis. Sintering was carried out at low temperature (900°C) to preserve the grains in a single-domain state. To perform sintering at such a low temperature, B₂O₃ or Bi₂O₃ was added to the hexaferrite. The effects of the amount and type of additive on the phase composition, microstructure, and magnetic properties of the sintered hexaferrite were studied. When Bi₂O₃ (in the form of 0.5, 1, or 3 wt % of Bi(NO₃)₃) was used, no changes in the phase composition occurred, while addition of B₂O₃ (in the form of 0.5, 1, or 3 wt % of H₃BO₃) resulted in a partial transformation of the hexaferrite to hematite α-Fe₂O₃. The average grain size of BaFe₁₂O₁₉ increased in response to increasing Bi₂O₃ or B₂O₃ concentration, but did not exceed the critical single-domain size. This provided for the high H_c values (370–420 kA/m) of the sintered samples, making them superior to most well-known brands of unsubstituted hexaferrites.