Hydrogen in layered iron arsenides: Indirect electron doping to induce superconductivity

Abstract

Utilizing the high stability of calcium and rare-earth hydrides, CaFeAsF1−xHx (x = 0.0–1.0) and SmFeAsO1−xHx (x = 0.0–0.47) have been synthesized using high pressure to form hydrogen-substituted 1111-type iron-arsenide superconductors. Neutron diffraction and density functional calculations have demonstrated that the hydrogens are incorporated as H− ions occupying F− sites in the blocking layer of CaFeAsF. The resulting CaFeAsF1−xHx is nonsuperconducting, whereas, SmFeAsO1−xHx is a superconductor, with an optimal Tc = 55 K at x ∼ 0.2. It was found that up to 40% of the O2− ions can be replaced by H− ions, with electrons being supplied into the FeAs layer to maintain neutrality (O2− = H− + e−). When x exceeded 0.2, Tc was reduced corresponding to an electron overdoped region.

Source-reported materials — not catalogue approval

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