Electron microscopic investigations were made of twin shape in the Cu3Ba2YO7 matrix of melt-textured pellets which contained dispersed particles of Y2BaCuO5. The images were compared with the shapes which were predicted, by thin twin-dislocation theory, for 3 regions (twin tip, root, intermediate). The twin-shape investigations yielded twin-boundary energies (60.0mJ/m2) which agreed with the values (46.5mJ/m2) that were obtained by relating the twin spacing to the local twin-colony size; as determined by the spacing between the Y2BaCuO5 particles in the same samples. The addition of Pt decreased the twin boundary energy to 26.8mJ/m2, as deduced using the twin shape method, and to 18.3mJ/m2, according to the interparticle twin-spacing method. The lattice frictional force, which resisted twinning dislocation motion, was also estimated from the minimum twin thickness and twin shape. The estimated frictional force agreed with the limit which was set by the reported de-twinning stress. The frictional force and de-twinning stress were expected to increase sharply with decreasing temperature. It was estimated that the critical length scale, where it was still energetically favorable to create twins instead of retaining elastic strain, with no twins, was equal to about 250nm.

Shape of a Twin as Related to the Inelastic Forces Acting on Twinning Dislocations in Cu3Ba2YO7. V.S.Boyko, S.W.Chan, M.Chopra: Physical Review B, 2001, 63[22], 224521 (8pp)