Crystal and Block Structures of Hexagonal Ferrites

It has been studied the crystal and block structures of the hexagonal ferrites with M, W, Y and Z types prepared by various coprecipitation-oxidation method. The structures have been refined with a Rietveld analysis of the powder X-ray diffraction pattern with high precision (R WP ＜0.09, R I ＜0.03). The density difference between the S-blocks was proportioned to the cobalt contents in hexagonal ferrites, but that between the R or T-blocks was relatively small. Compared with the blocks and cation-oxygen polyhedra in BaM (BaFe₁₂O₁?), those were bulky to the normal direction for the c-axis in Co2W (BaCo₂Fe₁?O₂?) and to the parallel direction for the c-axis in Co₂Y (Ba₂Co₂Fe₁₂O₂₂) and Co₂Z (Ba₃Co₂Fe₂₄O₄₁). The S-blocks of Co₂W, Co₂Y, and Co₂Z were unstable and distorted. Because the T-block of Co₂Z was unstable, the T-block was decomposed into the Ba-rich phase and Co₂W at high temperatures above 1200℃. A standard powder X-ray diffraction pattern for Co₂Z was proposed as well.