THE recent discovery of superconductivity in a number of alloys containing boron and carbon has revived interest in the field of intermetallic superconductors1-3. Although two structural forms have now been identified4-6, most of the new intermetallic supercon-ductors have a crystal structure typified by that of the quaternary alloy LuNi 2B2C, in which layers of rock-salt-structured LuC alternate with nickel boride tetrahedra4'5. The range of supercon-ducting intermetallic compounds was extended recently by the dis-covery of superconductivity in a system of quaternary boro-nitride alloys, La-Ni-B-N (ref. 7). Here we report the structure of the superconducting phase in this system, La3Ni2B2N3, together with that of the related non-superconducting phase, LaNiBN. We find that these two phases are members of a homologous series (LaN)n(Ni2B 2), with n Combining double low line 3 and n Combining double low line 2, respectively. Furthermore, our samples contain planar defects that suggest the existence of phases with larger n. Varying the number, n, of LaN layers within this system might thus provide a way to investigate the effect of dimensionality on the superconducting properties of intermetallics.
All Science Journal Classification (ASJC) codes