THE CRYSTAL-STRUCTURE OF SUPERCONDUCTING LUNI2B2C AND THE RELATED PHASE LUNIBC

SUPERCONDUCTING intermetallic compounds with relatively high transition temperature (T(c)) have been found in the systems Ln-Tr-B-C, where Ln is a lanthanide element (Y, Ho-Lu) and Tr a transition metal (Pd or Ni)1,2. In the nickel-bearing system, the superconducting phase has the formula LnNi2B2C (ref. 2). Although many structures are known for ternary carbides and borides, only a few have been reported for quaternary borocarbides3. Here we describe two new.phases that form in the Lu-Ni-B-C system: LuNi2B2C, a superconductor with a T(c) of 16.6 K (ref. 2), and LuNiBC, a closely related non-superconducting phase. The superconductor is a variant on the layered ThCr2Si2-type structure4, with additional carbon in the Lu plane. LuNiBC is derived from LuNi2B2C by adding another layer of Lu-C, producing a NaCl-type intergrowth. A new homologous series of intermetallic phases may be derivable from the simple building principles of these two structures.