The atomic structure of large-angle grain boundaries $\Sigma 5$ and $\Sigma 13$ in ${ m YBa_2Cu_3O_{7-\delta}}$ and their transport properties

摘要

We present the results of a computer simulation of the atomic structures oflarge-angle symmetrical tilt grain boundaries (GBs) $\Sigma 5$ (misorientationangles $\q{36.87}{^{\circ}}$ and $\q{53.13}{^{\circ}}$), $\Sigma 13$(misorientation angles $\q{22.62}{^{\circ}}$ and $\q{67.38}{^{\circ}}$). Thecritical strain level $\epsilon_{crit}$ criterion (phenomenological criterion)of Chisholm and Pennycook is applied to the computer simulation data toestimate the thickness of the nonsuperconducting layer ${\rm h_n}$ envelopingthe grain boundaries. The ${\rm h_n}$ is estimated also by a bond-valence-sumanalysis. We propose that the phenomenological criterion is caused by thechange of the bond lengths and valence of atoms in the GB structure on theatomic level. The macro- and micro- approaches become consistent if the$\epsilon_{crit}$ is greater than in earlier papers. It is predicted that thesymmetrical tilt GB $\Sigma5$ $\theta = \q{53.13}{^{\circ}}$ should demonstratea largest critical current across the boundary.