PHASE-EQUILIBRIA IN THE SYSTEM Y-NI-B-C

The phase content of powdermetallurgically prepared samples has been i nvestigated by means of chemical analysis, electron microprobe analysi s, optical microscopy, differential thermal analysis and X-ray diffrac tion studies. At 1300 degrees C the superconducting phase YNi2B2C is i n equilibrium with several well known phases as well as with YNiB4-zCz . The latter is a new compound, which crystallizes isotypic to YCrB4. The other equilibrium phases are the liquid phase (from which YNi4B an d Ni6.6B2.7C0.6 crystallize, the latter with the structure of Ni2B). Y B2C2, YNiC2 and YNiBC. Investigations of the homogeneity range of YNi2 B2C revealed boron deficiencies in dependence of the composition of th e sample. Additionally, YNi2B2C turned out to be thermodynamically sta ble up to 1500 degrees C. (C) 1997 Elsevier Science S.A.