Structure of grain boundaries in YBa2Cu3O7 thin-film step-edge junctions

Abstract

The atomic structure of 90 ~ [100] (or [010]) tilt grain boundaries in YBa2Cu307 thin-film step-edge junctions and, for comparison, in the interface between a-axis and c-axis oriented YBa2Cu307 grains is investigated by means of high-resolution transmission electron microscopy. For (100)(001)-type boundaries two different structures are found. In the first a (001) CuO2 plane of one grain faces a (100) Y-Ba-O plane of the other grain, in the second a (001) BaO plane faces a (100) Cu-O plane. In the former structure an incomplete unit ceil of YBa2Cu307 terminates at the boundary and a smaller strain in the adjacent CuO2 planes is detected in comparison with the latter. It is found that a combination of a partial dislocation with a "124" stacking fault is a way to accommodate the lattice mismatch between c and 3a of YBa2Cu307 in the boundary. For a symmetric (103)(103)-type boundary a displacement of the Cu-atoms of the CuO2 planes is found near the boundary plane. From this a redistribution of the oxygen atoms around the Y-atoms located right in the boundary plane is inferred. The possible effect of the boundary structure on the superconducting properties of YBa2Cu307 films is discussed.

Grain boundary evolution of YBa2Cu3O7−δ in the vicinity of steps on patterned (001) LaAlO3 substrates

“…The overlapping could also be a result of twist boundary or ͑013͒͑110͒ matching of planes at the boundary. [13][14][15] These 45°grain boundary parts were in agreement with the reports from Jia et al 2,12 Their presence is most likely due to a minimization of the grain boundary and YBCO surface energy once the a-axis and c-axis parts of the film met as the film thickness increased.…”

“…The nucleation and growth kinetics are thus essential for the grain boundary evolution and this may be the reason why vertical parts of the grain boundaries have not been observed previously. 2,12 The diffusion mean free path is a key factor since it will affect the nucleation probability on the step. This in turn determines the height of the vertical boundary part.…”