Fabrication of filamentary potassium-doped C 60 superconductors by suspension spinning method

Abstract

This paper describes the preparation of filamentary potassium-doped C 60 superconductors prepared by the suspension spinning method. Commercial C 60 powder was suspended in mixed poly(vinyl alcohol) solution of dimethyl sulfoxide and hexamethylphosphoric triamide (sample A). The viscous suspension was extruded as a filament into a precipitating medium of methyl alcohol and coiled on a drum. The filamentary sample was also prepared by the suspension spinning by using polyacrylonitrile solution of N, N-dimethylformamide (sample B). The samples were pyrolyzed to remove volatile components. Doping of potassium for the samples was prepared as following: At first, powder samples of nominal composition K 6C 60 was prepared by reaction of C 60 with excess potassium. The K 6C 60 powder and filamentary sample with stoichiometric ratio of K 3C 60 were placed in Pyrex glass tubes and vacuum-sealed and heated at 250 °C for 36 h. SQUID measurement shows the superconductivity of sample B with T c=18 K. On the other hand, the superconductivity more than 2 K was not detected for sample A.