  We investigated the effects of phosphorus substitution on the shape of the
Tc(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 {\alpha} 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-xHx with a Tc valley at x ~ 0.16. We found that
the Tc valley is located around (x, {\alpha}) ~ (0.16, 113{\deg}) for both
SmFeAs1-yPyO1-xHx and LaFeAsO1-xHx series, irrespective of changes in the Pn
anion and Ln cation species. This result suggests that suppression of Tc leads
to the emergence of a Tc valley when both the shape of FePn4 tetrahedra
represented by {\alpha} and electron doping level of x meet the above criterion
in 1111 type iron oxypnictide superconductors.
