  In this paper we report the synthesis of iron-based superconductors
CaFe2-xRhxAs2 using one-step solid state reaction method, which crystallizes in
the ThCr2Si2-type structure with a space group I4/mmm. The systematic evolution
of the lattice constants demonstrates that the Fe ions are successfully
replaced by the Rh. By increasing the doping content of Rh, the
spin-density-wave (SDW) transition in the parent compound is suppressed and
superconductivity emerges. The maximum superconducting transition temperature
is found at 18.5 K with the doping level of x = 0.15. The temperature
dependence of DC magnetization confirms superconducting transitions at around
15 K. The general phase diagram was obtained and found to be similar to the
case of Rh-doping Sr122 system. Our results explicitly demonstrate the
feasibility of inducing superconductivity in Ca122 compounds by higher
d-orbital electrons doping, however, different Rh-doping effect between FeAs122
compounds and FeAs1111 systems still remains an open question.
