Superhard Superconductive Composite Materials Obtained by High-Pressure-High-Temperature Sintering

Abstract

Superhard superconducting materials are of considerable interest for the creation of high pressure devices for investigating electrical and superconducting properties of various materials. The superconducting composites consisting of superconductors and superhard materials that are in thermal and electrical contacts may satisfy very conflicting requirements imposed on superconducting materials for special research cryogenic technique, wear-resistive parts of superconductor devices, superconducting micro-electromechanical systems (MEMS), etc. The design of materials combining such properties as superconductivity, superhardness, and high strength is an interesting task for both scientific and applied reasons. Superconducting composites may be used for the production of large superconducting magnetic systems (Gurevich et al., 1987). The discovery of superconductivity in heavily boron-doped diamonds (Ekimov et al., 2004; Sidorov et al., 2005) has attracted much attention. Superconducting diamonds are the hardest known superconductors. The potential applications of superconducting diamonds are broad, ranging from anvils in research high-pressure apparatus to supecronducting MEMS. However, the highest value of the superconductivity onset temperature in borondoped diamonds was found just about 7 K in thin CVD-grown films (Takano et al., 2004) and at about 4 K in bulk diamonds grown at high-pressure and high-temperature (Ekimov et al., 2004; Sidorov et al., 2005). In these pioneering works bulk polycrystalline diamonds with micron grainsize have been synthesized from graphite and B4C composition (Ekimov et al., 2004) and graphite with 4 wt% amorphous boron (Sidorov et al., 2005). The synthesis have been carried out at 8-9 GPa pressure and 2500-2800 K temperature in both cases. Later Dubrovinskaya et al., 2006, carried out synthesis of graphite with B4C composition at much higher pressure value 20 GPa but the same temperature of 2700K and found the superconducting state transition at lower temperature 2.4 1.4 K in the obtained doped polycrystalline diamonds. Due to the sharpening of the temperature interval of the superconductivity transition in magnetic field they suggested that superconductivity could arise from filaments of zero-resistant material. An alternative method for the creation of composite diamond superconductors was suggested by one of the authors of the present