CARBON IN YBA2CU3O7-X - ORIGIN AND EFFECTS

Residual carbon content in powders, sintered ceramics and textured sam ples was determined. Its source was shown to be essentialy the startin g material precursors. Carbon content may be reduced to below 600 ppm if no liquid phase is formed during precursor processing. The case of samples processed by solidification from a liquid is important. In sam ples textured on MgO substrate, carbon is supplied by this substrate. In this case, liquid phase plays an active role on the carbon retentio n in the YBa2Cu3O7-x structure during crystallisation. Magnetic suscep tibility behaviour of textured samples was analysed and discussed in r elation to the presence of carbon. A qualitative correlation between t he superconducting transition width and the carbon content was establi shed. A sharp superconducting transition at 91.5 K was achieved when c arbon content was less than 600 ppm.