Carbon-substituted MgB2 single crystals

Abstract Carbon-substituted MgB 2 single crystals, Mg(B 1− x C x ) 2 of 0.3–1.0 mm size were grown for x =0.02–0.15 by a high-pressure technique. The doping dependence of lattice constants studied in a range of x =0.0–0.2 shows a monotonic decrease in a , while the c parameter remains almost invariant. Using X-ray diffraction and Auger electron spectroscopy, the solubility limit of C in MgB 2 was estimated to be about 15 ± 1%, which is substantially larger than that reported for the polycrystalline samples synthesized by encapsulation techniques. Measurements of the temperature dependence of magnetization and resistivity showed a dramatic decrease in T c with C-substitution, followed by complete suppression of superconductivity for x >0.125. Resistivity measurements in magnetic fields parallel and perpendicular to the basal plane of the crystals showed a nearly isotropic state in the heavily doped crystals ( x >0.1).