Structural and superconducting properties of LaFeAs1−x Sb x O1−y F y

Abstract

We report the antimony (Sb) doping effect in a prototype system of iron-based superconductors LaFeAsO 1-y F y (y=0, 0.1, 0.15). X-ray powder diffraction indicates that the lattice parameters increase with Sb content within the doping limit. Rietveld structural refinements show that, with the partial substitution of Sb for As, while the thickness of the Fe 2 As 2 layers increases significantly, that of the La 2 O 2 layers shrinks simultaneously. So a negative chemical pressure is indeed "applied" to the superconducting-active Fe 2 As 2 layers, in contrast to the effect of positive chemical pressure by the phosphorus doping. Electrical resistance and magnetic susceptibility measurements indicate that, while the Sb doping hardly influences the SDW anomaly in LaFeAsO, it recovers SDW order for the optimally-doped sample of y=0.1. In the meantime, the superconducting transition temperature can be raised up to 30 K in LaFeAs 1-x Sb x O 1-y F y with x=0.1 and y=0.15. The Sb doping effects are discussed in term of both J 1 −J 2 model and Fermi Surface (FS) nesting scenario.superconductivity, crystal structure, doping effect, negative chemical pressure

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