Intersecting defect structures in gallia-and magnesia-doped rutiles

The possible { 210 } (0½0) defect intersection structures of rutile are analysed. There are 41 distinct intersection classes, 26 of which may exist as enantiomorphic forms. A classification scheme is introduced and used to analyse 386 observed intersections. Examples of 25 classes occur; eight of these account for 87% of the observations. The occurrence frequency may be understood by analysis of the stair-rod dislocation Burger's vector, required for continuity of the rutile structure around the intersection. Structural models for the commonly observed intersections and the nature of the 'dislocation-core' structures are presented. Exceptionally large tunnels are generated at orthogonal intersections and some high-resolution images are discussed. Statistical analysis shows that the distribution over the possible classes is not random, suggesting that an equilibrium network of intersecting defects may arise after long reaction times. The stability and mobility of intersections is expected to determine the kinetics of the reaction between rutile and dopants. Intersection structures may act as nuclei for low- to high-temperature phase transformations and they may aggregate and order to form new ordered structures.