Strained orthogonal twinning texture in the high-T c superconductor Ba2HoCu3O7−x

Two types of twinning texture involving four crystal orientations have been observed by transmission electron microscopy. The first type can be interpreted by a two-stage genetic model. A coarse twin is formed in the first stage and subsequently fine twin lamellae with 30 nm average width are formed in each of the two twin individuals. In the second type, two sets of twin lamellae merge nearly at a right angle, formingL-shaped andT-shaped regions. Each of these regions contains areas having two lattice orientations which differ by about 1° and by 2° in the extreme case, but the two lattices are coherently connected. The lattice planes at the junction of anL-shaped or aT-shaped region are bent continuously. There are two kinds ofL-shaped regions having different average widths of 30 nm and 60 nm, respectively. The lamellae averaging 30 nm in width form a network of lamellae.