The nature and extent of disorder within rapidly cooled TiO 1.9985

Abstract

A rapidly cooled sample of reduced rutile, composition TiO$_{1.9985}$, has been examined by high resolution electron microscopy at 500 kV, and images of crystallographic shear planes (c.s.p.) and other defects have been obtained in three major projections, namely $[\overline{11}1], [\overline{11}2]$ and [001]. Close examination of high magnification images of individual c.s.p. along [111] indicated the presence of extensive disorder. Consideration of structural models for the disorder, particularly in relation to the electron-optical imaging conditions, indicated that its nature and extent might be determined directly from appropriate high resolution images. Indeed, analysis indicated that the defect configurations along the various c.s.p. could be sequenced, which enabled an overall statistical impression of the disorder to be obtained. The mean orientation of the crystallographic shear (c.s.) defects was very close to {132}, but {132}-, {143}- and {121}-type segments were observed to occur with approximately equal frequency, with smaller numbers of other types, including {110}. The longitudinal ordering of c.s. steps was thus primarily very short-range. Similarly, a wide variation in lateral (dis)order was indicated by the range of defect-image widths observed, and many c.s.p. occurred as pairs rather than as isolated defects. The extent of this disorder in the c.s. defects appears consistent with a strong influence of the cooling rate on the c.s.p. formation. The methodology developed for sequencing the c.s. defects and analysing the disorder should prove invaluable in obtaining a fuller understanding of reduction-deformation reaction mechanisms in reduced rutile and other systems.