Superconducting Transition Temperatures of up to 47 K from Simultaneous Rare-Earth Element and Antimony Doping of 112-Type CaFeAs2

The effects of simultaneous Sb doping on the superconductivity of 112-type Ca1-xRExFeAs2 (RE = La, Ce, Pr, and Nd) were studied through measurements of the magnetization and electrical resistivity. In Sb-free materials, the superconducting transition temperature Tc of the La-doped sample was 35 K, while those of the Pr- and Nd-doped samples were ~10 K; no superconductivity was observed in the Ce-doped sample. Sb doping increased the Tc of all RE-doped samples: Tc increased to 47, 43, 43, and 43 K for RE = La, Ce, Pr, and Nd, respectively. We also found that the enhanced superconductivity results from the increase in the lattice parameter b, which increases the As-Fe-As bond angle to be closer to the ideal tetrahedron value. These observations provide insight for further increasing the Tc of the 112 phase.

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