A new family of superconducting fullerides, Na{sub 3}(NH{sub 3}){sub x}C{sub 60}(x = 2--8)
- and others
A series of A{sub 3}C{sub 60} fulleride superconductors (A is an alkali metal) with superconducting transition temperatures ({Tc}s) between 2.5 and 33 K has been reported. The {Tc}s of these materials are closely correlated to their f.c.c. lattice parameters, with the higher {Tc} materials having larger unit cell lengths. Recently, the {Tc} of the superconducting Na{sub 2}CsC{sub 60} has been raised from 10.5 K to 29.6 K by ammonia intercalation. The resulting intercalated compound, NaCs[Na(NH{sub 3}){sub 4}]C{sub 60} has an expanded unit cell compared to the starting material, with a larger cation Na(NH{sub 3}){sub 4+}, occupying the octahedral site. The sodium-doped C{sub 60} with nominal composition Na{sub 3}C{sub 60} however, does not show superconductivity and was reported to undergo a disproportionation reaction into two f.c.c. phases, Na{sub 2}C{sub 60} and Na{sub 6}C{sub 60} below 250 K. Here we report on the ammonia intercalation of Na{sub 3}C{sub 60}. Up to four superconducting phases with {Tc}s occurring near 6.7, 11.5, 13.5 and 16.5 K were observed in the compounds Na{sub 3}(NH{sub 3}){sub x}C{sub 60} (x {approx}2 = 8). All these phases gave significant superconducting shielding fractions (between 15 and 80% at 5 K). These compounds were characterized by use of AC susceptibility and SQUID measurements, TGA and x-ray powder diffraction.
- Research Organization:
- Argonne National Lab., IL (United States)
- Sponsoring Organization:
- USDOE, Washington, DC (United States); National Science Foundation, Washington, DC (United States)
- DOE Contract Number:
- W-31109-ENG-38
- OSTI ID:
- 10148936
- Report Number(s):
- ANL/CHM/PP--81405; ON: DE94011480; CNN: STC-91-20000
- Country of Publication:
- United States
- Language:
- English
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