Synthesis of nanocrystalline lithium zinc ferrites using polyacrylic acid, and their initial densification

A chemical synthesis technique that uses polyacrylic acid (PAA) to prepare nanocrystalline Li_0.3Zn_0.4Fe_2.3O₄ was investigated. Phase-pure spinel that had an average particle size of approx. 13 nm was synthesized at a low temperature (450°C) for 30 min. The average particle size was dependent on the firing temperature and amounts of PAA and Bi₂O₃. The combustion reaction of PAA was believed to be the main reason for the low-temperature synthesis of nanocrystalline lithium zinc (LiZn) ferrites. In addition, a chelating tendency was observed, via infrared (IR) spectroscopy, in the dried gel precipitates that were prepared at a low pH (approx. 2). The initial densification behavior of the nanopowder compacts was studied using linear-shrinkage data. Densification of the nanopowder without Bi₂O₃ started at low temperatures (approx. 400°C). The addition of Bi₂O₃ to the nanopowder noticeably did not contribute to reducing the initial densification temperature. This result was supported by the activation-energy calculation for the initial densification. Compared to an activation energy of 280 kJ/mol for grain-boundary diffusion of the nanopowder without Bi₂O₃, a higher value (430 kJ/mol) was obtained in the case of the 3 wt% Bi₂O₃-containing nanopowder.