Crystallographic texture analysis of YBCO superconducting bulks and thin films, and correlated physical properties
Etude de la texture cristallographique de ceramiques et de couches minces supraconductrices YBa2Cu3O7-d en relation avec les proprietes physiques
Résumé
this work deals with crystallographic texture analysis of ceramics and thin layers of YBCO, and with the texture effect on the superconducting properties, particularly on the critical current density.
X-ray diffraction was chiefly used, completed for specific samples by neutron diffraction and electron back scattering diffraction. We have developed the defocusing corrections needed for quantitative texture analysis of thin samples and multilayers, in the case of x-ray diffraction using the Schulz reflection geometry. Experimental conditions adapted to highly textured samples are detailed.
Highly textured bulk samples were elaborated by derived melt texture growth techniques. Under certain conditions, the texture is developed from the free surfaces of the sample. Generally, bulk textured samples exhibit two nearly oriented textures, which explain the relatively low measured Jcs. The "green" Y2BaCuO5 phase does not seemed textured in these samples. The texture and Jc relationship is clearly demonstrated in bulk samples, even if a quantitative description of the texture influence is still hard to establish.
In thin hetero-epitaxial layers, the observation of typical textures described in terms of near coincidence site lattices, allowed a quantitative texture analysis. Using a MgO(001) oriented single crystalline substrate, the interface region is very perturbated, giving rise to relatively bad superconducting properties of the layers (compared with other substrates offering better lattice mathching with YBCO). The Jc is quantitatively correlated to the texture degree of the films. Only weak volumic percentages of misorientations are necessary to strongly diminish Jc, while CuO precipitates can act in the opposite way.
Finally, texture analysis of experimental dispositives allows a quantitative characterisation of artificially generated misorientations, needed for the elaboration of Josephson junctions.
X-ray diffraction was chiefly used, completed for specific samples by neutron diffraction and electron back scattering diffraction. We have developed the defocusing corrections needed for quantitative texture analysis of thin samples and multilayers, in the case of x-ray diffraction using the Schulz reflection geometry. Experimental conditions adapted to highly textured samples are detailed.
Highly textured bulk samples were elaborated by derived melt texture growth techniques. Under certain conditions, the texture is developed from the free surfaces of the sample. Generally, bulk textured samples exhibit two nearly oriented textures, which explain the relatively low measured Jcs. The "green" Y2BaCuO5 phase does not seemed textured in these samples. The texture and Jc relationship is clearly demonstrated in bulk samples, even if a quantitative description of the texture influence is still hard to establish.
In thin hetero-epitaxial layers, the observation of typical textures described in terms of near coincidence site lattices, allowed a quantitative texture analysis. Using a MgO(001) oriented single crystalline substrate, the interface region is very perturbated, giving rise to relatively bad superconducting properties of the layers (compared with other substrates offering better lattice mathching with YBCO). The Jc is quantitatively correlated to the texture degree of the films. Only weak volumic percentages of misorientations are necessary to strongly diminish Jc, while CuO precipitates can act in the opposite way.
Finally, texture analysis of experimental dispositives allows a quantitative characterisation of artificially generated misorientations, needed for the elaboration of Josephson junctions.