Superconductivity in a high-temperature cubic phase of MoCx encapsulated in the multiwall carbon nanocages

By encapsulating inside the multiwall carbon nanocages, a high-temperature cubic phase α-MoCx can be successfully retained at room temperature. X-ray powder diffraction measurement for six samples reveals the single phase of the NaCl structure. The superconducting transition temperature of 9.30–11.83 K increases with decreasing d of 39–64 nm, where d is the mean diameter of encapsulated crystals. The transition is broad, extending over a temperature range from 2.6 to 3.6 K, and is discussed in terms of three characteristic lengths: d, the particular lengths Lc within which variations of composition cannot change drastically, and a coherence length ξ.