Carbon-substituted MgB2 single crystals

TL;DR

This study investigates how carbon substitution affects the structural and superconducting properties of MgB2 single crystals, revealing increased solubility and suppression of superconductivity with doping.

Contribution

It provides detailed analysis of lattice changes, solubility limits, and superconducting suppression in carbon-doped MgB2 single crystals, which was less explored before.

Findings

C solubility limit in MgB2 is about 15%

Superconducting transition temperature Tc decreases with C doping

Heavily doped crystals show nearly isotropic magnetic properties

Abstract

Carbon-substituted MgB2 single crystals, Mg(B_1-xC_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 MgB2 was estimated to be about 15(+/-)1%,which is substantially larger than that reported for the polycrystalline samples synthesized by encapsulation techniques. Measurements of temperature dependence of magnetization and resistivity showed a dramatic decrease in Tc 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).