A DISORDERED INTERMEDIATE STAGE IN THE REDUCTION OF TB11O20 OR TB7O12 TO C-TYPE TB2O3 IN THE ELECTRON-MICROSCOPE

A thin crystal of Tb//1//1O//2//0 with a patch of Tb//7O//1//2 has been observed to reduce in the high-resolution electron microscope to Tb//2O//3 (C-type). In both cases the reduction occurred through a disordered intermediate stage which was of fluorite structure. The Tb//2O//3 was observed to grow into this disordered region in patches previously termed cooperative emergence in a nucleation controlled ordering process. Whereas transformation (reaction) between Tb//1//1O//2//0 and Tb//7O//1//2, for example, would be expected to be cooperative and displacive, the transformation to a C-type structure would be reconstructive and, thus, the intermediate stage of disorder is not unexpected.