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We report on the scaling relation between the Hall and longitudinal resistivities, ρH∝ρβ, in an unidirectionally twinned YBCO thin film, for current flowing parallel and perpendicular to the twin boundaries for high magnetic fields. Our results are discussed in the framework of existing models for anisotropic pinning.

The successful achievement of high temperature superconductor (HTS) YBa 2 Cu 3 O 7 films by MOCVD is not straightforward and depends critically on the volatility and stability of the precursor materials which must be transformed into the product film. In the present study, new deposition processes based on mixed liquid sources are described, where the unstable precursor is preserved from thermal decomposition and where the film growth rates can be considerably improved. For the synthesis of YBa 2 Cu 3 O 7 , these processes, named aerosol-assisted MOCVD, injection MOCVD and band-injection MOCVD, use a single solution source of Y, Ba and Cu β-diketonates dissolved in suitable organic solvents. Experimental details of these new processes are described and the effects of different process parameters are studied in relation with the quality of the deposited layers. Thin and thick films of YBa 2 Cu 3 O 7 and buffer layers (CeO 2 , SrTiO 3 ,……) have been grown using these processes. The superconducting properties of the high quality films obtained ( T c = 90 K, J c > 10 6 A cm −2 at 77 K) will be discussed in view of their use for large scale applications.

The technique used for the control of the injection of fuel in thermal motors has been applied to the generation of active gases for MOCVD layers deposition. A wide variety of compounds and multilayers have already been grown using this new CVD source (from simple cxides, nitrides or metals to complex ternary oxides). Using two injection sources working sequentially, stackings like YBa2Cu307/CeO2 or SrTiO3/YBa2Cu3O7 double layers, Ta2O5/SiO2 amorphous or crystallized multilayers and SrTiO3/BaTiO3 or YBa2Cu3O7/PrBa2Cu3O7 epitaxial superlattices have been synthesized. The injection MOCVD seems to be a very promising technique for the stacking of multicomponents oxides having different electronic properties. This opens the way for the synthesis of a wide set of artificial materials, exhibiting completely new properties that cover a very large range of potential applications. After a description of the technique, we will demonstrate its performances on some results obtained on the synthesis of dielectric and ferroelectric layers and multilayers.

A self-tuning approach to the growth of lead-containing complex oxide films free of secondary phases was developed. Due to the volatility of lead oxide one can establish the process conditions when the phase purity is provided in spite of any fluctuations of the mass fluxes. An additional advantage is suppression of the surface roughening with the increase of the film thickness providing high smoothness (S a = 1.2-1.5 nm) at the deposition rate up to ∼1μm/h. The effect is due to the quasi-liquid PbO-based surface layer activating the surface diffusion during the film growth. This approach was successfully used for the growth of single phase epitaxial CMR La 1-x Pb x MnO 3 (x=0. 1-0.6), ferroelectric PbTiO 3 films, scintillator material PbWO 4 and the multilayers which were characterised by XRD, SEM, EDX, RBS, HREM, AFM, electric and magnetic measurements.

We report on the angular dependence of the magnetoresistance in YBCO/PBCO multilayers with thick PBCO layers, in magnetic fields up to 16 T and with an angular resolution of 0.01°. From these measurements, the anisotropy parameter was extracted, presenting an unexpected field and angle dependence. These results are interpreted as a consequence of vortex shape effects in the thin decoupled YBCO layers.

EuBa 2 Cu 3 and YbBa 2 Cu 3 microcrystalltne alloys obtained by rapid solidification have been oxidized completely in flowing oxygen at a temperature higher than 900° C with subsequent slow cooling and have yield the high temperature oxides EuBa 2 Cu 3 7−δ and YbBa 2 Cu 3 O 7−δ . The onset of superconductivity occured at 92 K in the case of Eu and at 89 K in the case of Yb. The resistivity in the normal state ( ρ at 100 K) is lower than in sintered powder materials Sue to a better compaction and to a better intergrain coupling.

In order to understand the superconductive behaviour of the new high Tc superconductors, many experiments have been carried out. Among these, the measurements of a. c. complex susceptibility x = x′ + ix″ as a function of temperature are of great interestl. The in-phase component x′, corresponding to inductive variations, indicates perfect diamagnetism and flux shielding. The out-of-phase component x″, corresponding to resistive losses, can behave differently depending on which loss mechanism is involved. In the (RE) Ba2Cu3O7−δ oxides, the observed magnetic behaviour has been analyzed by several authors in terms of percolation, junctions, disorder or superconducting inclusions4,7 with the physical data apparently varying from one sample to another, depending on the synthesis methods and on the different heat treatments used. We have, therefore, performed inductive a. c. complex susceptibility as well as d. c. resistive measurements on sintered bulk and powdered samples of HoBa2Cu3O7−δ and on two types of YBa2Cu3O7−δ samples in order to correlate the resistivity, the morphology and the diamagnetic behaviour in these granular high Tc superconductors. The observed phenomena are directly dependent on the contact resistance between the grains (i. e. the ability of carrying supercurrent) and on the surface to volume ratio of the grains in a given material.