ON THE SYNTHESIS AND THE ELECTRIC AND MAGNETIC-PROPERTIES OF SUPERCONDUCTING BARIUM-NIOBIUM-OXIDE COMPOUNDS

In the system Ba-Nb-O-N a superconducting ceramic material with T-c = 22 K was synthesized. The temperature dependencies of magnetic suscept ibility and resistivity of these ceramics with different oxy en concen trations was studied. A large increase of T-c was observed, from 12 K for samples prepared in O-2 up to 23 K prepared in air due to the vari ation of oxygen composition and Y doping. The XRD structure and Auger electron spectroscopy composition investigations indicate the formatio n of oxinitrides BaNbOxNy, with a cubic structure having a lattice par ameter alpha = 4.32 Angstrom, which is apparently responsible for the highest T-c observed. The incorporation of nitrogen into the crystal l attice results in an increase of T-c and stabilization of the supercon ducting structure. (C) 1997 Elsevier Science B.V.