Phys. Rev. B 79, 184516 (2009) [5 pages]Unusual doping dependence of superconductivity in NayFeAsReceived 2 March 2009; revised 14 April 2009; published 18 May 2009 Superconductivity and phase relationships were explored in the Na-Fe-As system. The PbFCl-type 111 phase is stable only within a Na stoichiometry range of 1.00 to ∼0.85, and exhibits bulk superconductivity within an even narrower range around 0.90 in Na0.9FeAs. In particular, stoichiometric NaFeAs is not a bulk superconductor. The onset of the superconducting transition varies in a totally different way and the highest Tc occurs in multiphase samples with a nominal composition of Na:Fe:As=0.5:1:1, where the superconductive volume-fraction is almost zero. Such doping dependency is rather surprising and in disagreement with most expectations. © 2009 The American Physical Society URL:
http://link.aps.org/doi/10.1103/PhysRevB.79.184516
DOI:
10.1103/PhysRevB.79.184516
PACS:
74.70.Dd, 74.62.Dh, 74.62.Bf
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