Chemical and Superconducting Properties of the Quaternary Borocarbides Ln-M-B-C (Ln=rare earths, Y; M=Ni, Pd)

We present a status report on the quaternary rare-earth transition metal borocarbides. We discuss in particular the superconducting and magnetic properties of LnNi2B2C (Ln=rare earths, Y) in connection with sample preparation and composition. We also report new results on the analysis of the chemical composition of the superconducting phase at 23 K in the Y-Pd-B-C system, using electron microprobe and, for the first time in these materials, nuclear microprobe. We will briefly comment on new borocarbides and other related systems