Effect of nucleating agents on the crystallisation behaviour of barium hexaferrite in a borate glass

Abstract

Glass-ceramics containing BaFe₁₂O₁₉ as the major crystalline phase have been prepared from glasses in the system BaO-Fe₂O₃-B₂O₃ by subjecting the latter to a suitable heat treatment schedule. Small concentrations (up to 1 mol%) of Ag₂O, Bi₂O₃, P₂O₅ and TiO₂, respectively, have been used to improve the crystallisation kinetics of the ferrite phase. Bi₂O₃ is found to be the most efficient nucleating agent in this process whereas TiO₂ inhibits the precipitation of any ferrite phase in the glass matrix. Detailed magnetic and EPR measurements have been carried out on all the glass ceramics prepared. The data are explained on the basis of microstructural characteristics as delineated by optical and transmission electron microscopy.