Production of carbon doped boron to synthesize high performance MgB2 superconductor

MgB2 has been known almost six decades although its superconductive property is discovered only in 2001. Since then the usage in superconductive wires, coils and magnets became quite common due to its convenience and cost-effective availability. MgB2 is a unique superconductor when it comes to critical temperature (Tc = 39 K) occupying middle place between the so called low temperature (LT) superconductors (e.g. NbTi, 9K) and the high temperature BSCCO (Bismuth strontium calcium copper oxide) which is 108 K. Superconductors need to reach these critical temperatures in order to work efficiently. MgB2 can be easily cooled by the usage of liquid hydrogen or solid state nitrogen/cryocooler that is readily available at a significant cost difference. In this study we aimed to improve the superconductivity properties of MgB2 by doping with different carbon containing sources (sugar and malic acid) at mass percentages of 3, 6 and 9. In the preliminary experiments, malic acid and sugar were decomposed under thermogravimetric conditions (DTG, Ar) and the weight changes, the temperature of decomposition and formation of pure carbon (ca. 400 C) were determined. The addition of Mg at this stage is not favorable due to presence of the water which forms during the decomposition of the precursor's malic acid and sugar. The phase purity of the samples was analyzed by X-Ray diffraction method. For the determination of the lattice constants in each sample Rietveld analysis performed. To obtain numerical precession from the XRD the measured reflections were calibrated with the well-known Si standard. The results show the expected shifts in the lattice parameters a and c axes with respect to the pure MgB2. Very typical hereby is the increase of the c/a ratio in the doped specimen proportional to the amount of C insertion into the lattice of MgB2. Starting from the same nominal carbon contents, the doping with sugar is more effective than when malic acid was employed as C-precursor. We believe that this is directly related to the homogeneity of the reactants - and particularly to that of carbon - in the overall process.