Thickness dependence of the twin density in YBa2Cu3O7−δ thin films sputtered onto MgO substrates

The lengths and spacings of twins in YBa2Cu3O7−δ thin films deposited onto MgO substrates have been measured by transmission electron microscopy as a function of film thickness t, for t ranging from 50 to 1400 nm. The twin length is linear in t, while the twin spacing follows a t1/2 dependence. This form for the twin spacing is consistent with the prediction of a simple free energy expression for the twinning transformation.