Changes in microstructure of oriented Ba₃Co₂Fe₂₄O₄₁ material during sintering. I

Samples of the ferrimagnetic material Ba₃Co₂Fe₂₄O₄₁, prealigned in a rotating magnetic field and sintered at 1260°C, have been examined for (1) preferred orientation, (2) grain growth, and (3) porosity. The quantitative orientation of the fibre texture obtained in the samples measured by means of the (0001) pole figures, increases with sintering time. The maximum in the (0001) pole figures appears to be a linear function of the average intercept line length measured on sample surfaces perpendicular to the [0001] fibre axis. The relationship of texture and average intercept line length can be explained theoretically if it is assumed that the well oriented crystallites in the samples grow at the expense of the poorly oriented ones resulting in a decrease in number of the latter crystallites, whereas their averaged size remains unchanged. The transport mechanism of the densification process of the material used could not be determined. With the sintering equations given by Johnson [J. Amer. Ceram. Soc. (1970). 53, 574-577] the two transport mechanisms, viz. grain-boundary and volume diffusion are possible. However, from the fact that the bulk porosity and the area pore fraction of the sample surfaces seem to be approximately proportional to the averaged intercept line length the conclusion may be drawn that the densification occurs most probably by volume diffusion.