L. Hou

Single variant orientational growth of YBa2Cu3O7−x on vicinal (011) SrTiO3 substrates observed by electron microscopy

Abstract The results of a transmission electron microscopy (TEM) and X-ray microanalysis (EDS) study of YBa 2 Cu 3 O 7− x (YBCO) films grown on vicinal (011) SrTiO 3 substrate are presented. The YBCO films tend to be single crystalline grown in single variant orientation with c -axis ≈45° from the surface. Cracks, second phase precipitates (CuO and Y 2 O 3 ), and a few small YBCO grains in other orientations were revealed in the films.

Biaxially aligned (013) films on vicinal (011)

Epitaxial (013) films have been grown by pulsed laser deposition onto exact and vicinal (011) substrates. X-ray diffraction measurements showed that the films contained two mirror-related orientations when grown on exact (011) surfaces, but that a strong preference for only one of the two (013) orientations developed when the substrate surface was tilted by about toward the direction. The inclination removed the two-fold symmetry of the surface to induce this preference, resulting in a film with (013) film (011) substrate and [100] film [100] substrate. Films with a single (013) orientation may offer some distinct practical advantages over other monocrystalline film orientations.

Control of epitaxial growth orientation in YBa 2 Cu 3 O 7−δ films on vicinal (110) SrTiO 3 substrates

Films of YBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}} (YBCO) were grown on (001), exact and vicinal (110), and (111) SrTiO{sub 3} single crystal substrates by pulsed laser deposition, and evaluated by x-ray diffraction and scanning force microscopy (AFM). It was observed that the YBCO was always epitaxially aligned to the substrate with the [001] ({ital c}-axis) parallel to a substrate cube axis direction. For the exact (001), (110), and (111) surfaces, there were one, two, and three orientations, respectively. For the vicinal (110) surfaces, however, there was usually only one discernible {ital c}-axis orientation, corresponding to a single {l_brace}013{r_brace} film surface orientation. The reduction of the (110) surface twofold symmetry by use of a vicinal substrate thus allowed controlled growth of a YBCO single crystal with an inclined {ital c}-axis orientation. {copyright} {ital 1998 Materials Research Society.}

Correlation length and time in the vortex-glass critical regime in YBa2Cu3O7−x films

Abstract We report on the complex conductivity of a YBa2Cu3O7−x microbridge in the presence of magnetic field 0.5 ≤B≤6.5 T applied parallel to the c-axis. A broad range of frequences 10 ≤ f ≤ 2 × 106 Hz for the transport current passing through the bridge allows us to explore the ac dynamical response of the vortices where conflicting results have been reported, in addition to the static characteristics of the vortex system (dc limit). In consistency with the concept of a correlation length and a correlation time that diverge at the transition temperature Tg(B), we demostrate that a single value for Tg(B) can be identified in both the static and dynamical measurements, within an experimental uncertainty of 1 K. In conflict to previous reports, the real and imaginary components of the ac-linear voltage at T=Tg(B) were found to follow the same power law Vi ∝ Vo ∝ fα, with α=0.82±0.05. Finally, as T→Tg+, the critical scaling laws break down when the diverging vortex correlation length matches the film thickness of our sample and the correlation time exceeds 10 μs.