Ba Doping Effects on the Superconductivity and Electronic Structure of K2Mo3As3

The doping effects of alkaline earth metal Ba on the quasi-one-dimensional superconductor K2Mo3As3 have been systematically investigated. A series of polycrystalline samples (K1–xBax)2Mo3As3 with nominal doping level x from 0 to 0.9 were fabricated. Ba2+ cations were found to selectively substitute K+ cations on the 1c site, forming a new orderly doping phase (K0.75Ba0.25)2Mo3As3, and no intermediate phase was discovered. (K0.75Ba0.25)2Mo3As3 adopts the same crystal structure as K2Mo3As3 with the space group P–6m2 (No. 187). Neither magnetic susceptibility nor electrical resistivity measurement reveals bulk superconductivity above 2 K. The absence of superconductivity can be explained by the evolution of energy bands with electron doping, as revealed by the calculation of band structures. The site-selective substitution is also revealed to be a generic behavior in the 233-type CrAs/MoAs-based compounds, which may lead to the finding of similar chemical phases.