High quality twin-free c-axis oriented YBa₂Cu₃O_7-δ films were grown by pulsed laser deposition on NdGaO₃. We find resistive anisotropies between 1 < ρ_a/ ρ_b < 1.6. The resistive anisotropy above T_c appears to be correlated to the anisotropy in the critical current below T_c. The normal state properties of the chains along b seem to have a significant influence on the superconducting properties of YBa₂Cu₃O_7-δ.

A new method has been developed to synthesize compact yttriumtrihydride by making use of a thin film technique. For electrical measurements yttrium films of typically 500 nm thickness are covered under UHV conditions by a 5 nm thick palladium overlayer which consists of electrically disconnected islands. Loading of these films with hydrogen up to the trihydride phase can then be done ex-situ in a reasonably short time (around 20-40 h) by applying gas pressures of about 60 × 10⁵ Pa. For a thicker Pd layer (above 20 nm) this time can be considerably shorter (t ∼ 125 s). The film morphology stays intact during the loading process although the film thickness increases by approximately 11% and the crystal structure changes from h.c.p. to f.c.c. and back to h.c.p. These samples are, therefore, very well suited for an investigation of the remarkable electrical and optical properties of trihydrides, as recently reported by Huiberts et al. (Nature, 380, 1996, 231). In this article we give evidence for the island structure of the palladium overlayer and make a comparison of a number of physical properties of yttrium and its related hydrides as thin films with literature values for the same material in bulk form. These properties include lattice parameters for the different hydride phases, electrical resistivity for yttrium and its dihydride and Hall coefficient for yttrium. The characteristics of the yttriumhydride thin films are very similar to those of bulk material. Furthermore, we performed concentration measurements and resistivity measurements during hydrogen loading. It is shown that the resistivity rises three orders of magnitude when yttrium is loaded up to the trihydride phase at 60 × 10⁵ Pa.

Low-electric-field E-js curves, normalized dynamical relaxation rate Q(T)=d ln(js)/d ln(E), and experimental critical current density js(E=Ec) were measured from 10 to 85 K with the magnetic sweeping method. By taking a general assumption for the activation energy U(js,T)=Uc(T)f[js(T)/jc(T)], with t=T/Tc, we obtained the U(j,T=0 K) relation by scaling all the E-js curves of different temperatures to one smooth curve with Uc(T) and jc(T) determined by the so-called generalized inversion scheme. It is shown that the important parameter c=ln(v0B), which was actually taken as a fitting parameter in the scaling process in previous work, can be predetermined. It is also found that the resulting U(j,T=0 K) relation based on the E-js curves for T 79 K can be well interpreted with the collective-pinning model. However, the data for T>79 K start to deviate from this interpretation, which may be attributed to the reverse hopping of vortices.