  By substituting the Fe with the 4d and 5d-transition metals Rh, Ir and Pd in
SrFe_2As_2, we have successfully synthesized a series of superconductors
SrFe_{2-x}M_xAs_2 (M = Rh, Ir and Pd) and explored the phase diagrams of them.
The systematic evolution of the lattice constants indicated that part of the Fe
ions were successfully replaced by the transition metals Rh, Ir and Pd. By
increasing the doping content of Rh, Ir and Pd, the antiferromagnetic state of
the parent phase is suppressed progressively and superconductivity is induced.
The general phase diagrams were obtained and found to be similar to the case of
doping Co and Ni to the Fe sites. However, the detailed structure of the phase
diagram, in terms of how fast to suppress the antiferromagnetic order and
induce the superconductivity, varies from one kind of doped element to another.
Regarding the close values of the maximum superconducting transition
temperatures in doping Co, Rh and Ir which locate actually in the same column
in the periodic table of elements but have very different masses, we argue that
the superconductivity is intimately related to the suppression of the AF order,
rather than the electron-phonon coupling.
