Carbon in YBa 2Cu 3O 7− x: origin and effects

Abstract

Residual carbon content in powders, sintered ceramics and textured samples was determined. Its source was shown to be essentialy the starting 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 samples textured on MgO substrate, carbon is supplied by this substrate. In this case, liquid phase plays an active role on the carbon retention in the YBa 2Cu 3O 7− x structure during crystallisation. Magnetic susceptibility behaviour of textured samples was analysed and discussed in relation to the presence of carbon. A qualitative correlation between the superconducting transition width and the carbon content was established. A sharp superconducting transition at 91.5 K was achieved when carbon content was less than 600 ppm.