Epitaxial growth and critical currents in (013)/(103)- and (110)-orientedYBa2Cu3Oxfilms

Thin films of ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{\mathit{x}}$ were grown epitaxially on (110)-oriented ${\mathrm{SrTiO}}_3$ crystals using in situ, off-axis, rf magnetron sputter deposition. The films were investigated by x-ray diffraction, reflection high-energy electron diffraction, scanning electron microscopy, resistance-temperature, and critical current measurements. Depending on growth conditions, the films formed platelets oriented with ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{\mathit{x}}$ (110) or (013)/(103) parallel to the (110) substrates. Direct comparison of simultaneous growth on (110)- and (100)-oriented substrates showed that the critical temperature was significantly less for growth on the (100) surface for the same growth conditions. This is ascribed to the more open structure of the (110) and (013)/(103) planes which allow more complete oxidation of the film during growth and cool down. For growth on (110) substrates and substrate temperatures below about 650 °C the (110) orientation dominated; above 650 °C the films were mainly (013) or (103) oriented. The critical current density for the (013)/(103)-oriented films was 0.25 MA ${\mathrm{cm}}^{\mathrm{-}2}$ at 77 K. This compares with about 5 MA ${\mathrm{cm}}^{\mathrm{-}2}$ for ${\mathit{J}}_{\mathit{c}}$ parallel to the ab plane and 10 kA ${\mathrm{cm}}^{\mathrm{-}1}$ for ${\mathit{J}}_{\mathit{c}}$ parallel to the c axis. The temperature dependence of the (013)/(103) films was ${\mathit{J}}_{\mathit{c}}$∝(1-T/${\mathit{T}}_{\mathit{c}}$ ${)}^{3/2}$, 0.9${\mathit{T}}_{\mathit{c}}$T${\mathit{T}}_{\mathit{c}}$. This suggests that the measured critical currents correspond to the depairing current, although intergranular twinning gives a similar temperature dependence. The overall results are discussed in relation to the nucleation and growth kinetics of the different epitaxial modes and also the effects of energetic particles on sputter deposition.