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. 
Kazutaka Kudo, Yutaka Kitahama, Kazunori Fujimura, Tasuku Mizukami,   Hiromi Ota, Minoru Nohara
cond-mat.supr-con