Changes in microstructure of oriented Ba₃Co₂Fe₂₄O₄₁material during sintering. II

Abstract

Pellets of the ferrimagnetic material Ba3Co2Fe2.,Oa~ were sintered at temperatures between 1220-C and 1310"C in (1) a non-oriented state, (2) with a fibre texture generated by a rotating magnetic field during pressing and (3) with a fan texture due to a static magnetic field. During sintering up to 24 h. the changes in texture sharpness and density were studied. Textured samples attained a higher ultimate density than non-oriented ones and those with fibre texture became densest. To determine the sharpnesses of the texture the maximum standardized intensities of the reflexions 0,0,0,14, 1,0,1,16, 1,1,5,10 and 11_~0 were calculated from the experimental intensities. The mutual relations of the maximum standardized intensities of the four reflexions were given by representing the intensities of these reflexions for both textures as polynomials. The dependence of sharpness of texture on position in the pellet has been determined. It followed that this sharpness had to be averaged over the height of the pellet, to get a representative value for the whole pellet. Both kinds of texture were found to sharpen during normal grain growth, but during exaggerated grain growth in the last stage of sintering the sharpness of the fibre texture decreased, whereas that of the fan texture still increased. A possible explanation of this phenomenon is given on the basis of the different characters of these textures. A linear relationship is found between sharpness of texture and area porosity during normal grain growth. The compound starts decomposing at a lov~er temperature than that given in literature.

Multiferroic and Magnetoelectric Hexagonal Ferrites

“…This growth is much greater in the direction of the hexagonal plane, perpendicular to the c-axis [61]. The grain size becomes even more exaggerated by DGG after 1,260°C/10 h, 1,290°C/10 h or 1,300°C/10 min, giving huge plates tens or even hundreds of lm in diameter, but still only a few lm thick, and with a corresponding loss of density in the final product, probably as pores are enclosed within the grains [62].…”

Hexagonal Ferrite Fibres and Nanofibres

“…This growth is much greater in the direction of the hexagonal plane, perpendicular to the c-axis [105]. The grain size becomes even more exaggerated by DGG greater sintering temperatures or times, giving huge plates tens or even hundreds of µm in diameter but still only a few µm thick, and with a corresponding loss of density in the final product, probably as pores are enclosed within the grains [106]. [141].…”