Controlling factors of Tc dome structure in 1111-type iron arsenide superconductors

We investigated the effects of phosphorus substitution on the shape of the T-c (x) dome in 1111-type SmFeAs1-yPyO1-xHx (0 < x < 0.5). Hydride ion substitution of oxide sites (O2--> H-) exerts a chemical pressure effect, i. e., a structural reduction of the Pn-Fe-Pn angle alpha (Pn = P, As) and also dopes electrons into the FePn layer to induce superconductivity. Isovalent phosphorus substitution (P3- -> As3-) can induce only a chemical pressure effect, i.e., an increase of a for La substitution of Sm sites. As y increases from 0.0 to 0.5, the single Tc dome gradually splits into two domes, similar to those of LaFeAsO1-x H x with a T-c valley at x approximate to 0.16. We found that the Tc valley is located around (x, alpha) approximate to (0.16, 113 degrees) for both of the SmFeAs1-yPy O1-xHx and LaFeAsO1-x H-x series, irrespective of changes in the Pn anion and Ln cation species. This result suggests that suppression of T-c leads to the emergence of a Tc valley when both the shape of FePn(4) tetrahedra represented by a and electron-doping level of x meet the above criterion in 1111-type iron oxypnictide superconductors.