The structure of solidification-processed material was investigated by means of X-ray diffraction and transmission electron microscopy. It was usually assumed to have the tetragonal C11b MoSi2 structure and the stoichiometry of ReSi2. It was found here that the disilicide exhibited an off-stoichiometric Si-deficient composition of Re4Si7. In addition, several structural instabilities were observed; including an orthorhombic distortion of about 0.6% from the tetragonal C11b MoSi2 structure, with spot-splitting across the {110} twin plane. There was also a discommensuration along the a-axis, with a periodicity of 1.3nm. There was another longer period modulation along the c-axis. There was a weak monoclinic distortion in some specimens, as revealed by spot-splitting in the high-order Laue zone reflections of [100] diffraction patterns; accompanied by twinning on the (001) planes. Finally, there were much larger distortions in some [010] patterns; plus a chevron structure which was suggested to result from a displacive transformation. The structural anomalies were thought to be related to the stoichiometry of Re4Si7, which could result in a composite modulated structure in which the Si sub-lattice had a larger average periodicity along the a-axis than the Re sub-lattice.

Incommensuration and Other Structural Anomalies in Rhenium Disilicide. A.Misra, F.Chu, T.E.Mitchell: Philosophical Magazine A, 1999, 79[6], 1411-22