The origin of preferential twinning in YBa2Cu3O7−δ thin films deposited on the (0 0 1) NdGaO3 substrate

With few exceptions, YBa2Cu3O7−δ thin films have been shown to be heavily microtwinned. Conflicting reports of twin-free films, however, have been presented when using the (0 0 1) NdGaO3 substrate. In this report, we address this issue as well as investigate the epitaxial relationship between YBa2Cu3O7−δ and this substrate. We find no evidence that the films are twin-free, but instead provide corroborative support for other work showing that the films are preferentially twinned. This work also establishes the epitaxial relationship between the film and substrate; a relationship consistent with the formation of preferential twins.