Intralayer carbon substitution in the MgB2 superconductor -: art. no. 134513

We report that the ternary MgB2-xCx compounds adopt an isostructural AlB2-type hexagonal structure in a relatively small range of nominal carbon concentration, x<0.1. The lattice parameter a decreases almost linearly with increasing carbon content x, while the c parameter remains unchanged, indicating that carbon is exclusively substituted in the boron honeycomb layer without affecting the interlayer interactions. The superconducting transition temperature T-c decreases quasilinearly as a function of the carbon concentration. with a slope steeper than that for the isoelectronic Mg1-xAlxB2.