Use of preceramic polymers for magnesium diboride composites

• Published in: Physica. C, Superconductivity Vol. 480; pp. 102 - 107
• Main Authors: Sandu, V., Cimpoiasu, E., Aldica, G., Popa, S., Sandu, E., St. Vasile, B., Hurduc, N., Nor, I.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01.10.2012; Elsevier
• Subjects: Borides; Carbon doping; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Critical current; Critical currents; Exact sciences and technology; Magnesium; Magnesium compounds; MgB2; Nanostructure; Physics; Polymer matrix composites; Polymers; Polysiloxane copolymer; Polysiloxanes; Properties of type I and type II superconductors; Pyrolysis; Spark plasma sintering; Superconductivity; Pyrolysis; Carbon doping; Polysiloxane copolymer; Spark plasma sintering; Critical current; MgB2; Critical current density; Pair breaking; Impurity density; Superconducting transitions; Doping; MgB; XRD; Nanostructures; Critical field; Carbon additions; Composite materials; Magnesium boride; High-Tc superconductors; Microstructure
• ISSN: 0921-4534; 1873-2143
• DOI: 10.1016/j.physc.2012.03.052

► We used polysiloxane copolymers for improving transport properties of MgB2. ► Polysiloxane-co-vinyl-ferrocene was used to insert magnetic nanoparticles. ► Cyclic polysiloxane-co-styrene leads to the best critical properties. ► Magnetic pinning is visible at high temperatures in samples with ferrocene. We used preceramic polysiloxane polymers to fabricate superconducting MgB2 composites that are doped with carbon and nanosized inclusions to improve the pinning properties. The polysiloxanes were prepared by atom transfer radical polymerization and the composites were fabricated by the short time spark plasma sintering method. We found that the superconducting critical temperatures were higher than expected from the carbon content found from the X-ray diffraction analysis of the (110) peak of MgB2. To explain this finding we propose that the grains are unevenly doped, with a core–shell distribution. We also found that both, the upper critical fields and the critical current densities are higher in the preceramic-doped samples than in pure MgB2, in agreement with the carbon doping level. When ferrocene-grafted polysiloxane is used, the upper critical field is the largest, while the critical current density is the lowest. We attribute this fact to the fact that the polymer pyrolysis results in iron-based nanostructures which have a pair breaking effect.