MOSSBAUER MEASUREMENTS OF SOLID SOLUTIONS (Fe_xCr_(1-x))_2O_3, 0＜x＜1

摘要

The crystal structure of both oxides is given by hcp (hexagonal closed packed) O~(2-) ions, where the cations occupy octahedral holes (figure 1) only. The layers of the hcp structure are denoted by A and B. The x-y coordinates of the cations correspond to the C layer of the fcc close-packed structure. The relation of cations to anions is 2:3 . Therefore not all of the possible octahedral sites are filled, which gives rise to the hexagonal substructure (see figure 2). In figure 3a the hexagonal elementary cell of corundum is drawn. From the six C-layers plotted only three are necessary in the case of corundum structure. The cation sites are marked as dots. The unoccupied octahedral sites (compare figure 1) are arranged in such a way, that they are on different x-y positions in neighbouring layers. As indicated in figure 3a, the electrostatic repulsion of neighbouring cations gives rise to a small deviation from the ideal structure. These deviation will be further ignored.