Structural and Physical Properties of Ca1−xSrxFe2As2 (0≤x≤1.0) and Ca0.5Sr0.5Fe2−yCoyAs2 (0≤y≤0.6)

The Ca1−xSrxFe2As2 (0≤x≤1) and Ca0.5Sr0.5 Fe2−yCoyAs2 (0≤y≤0.6) materials were prepared by a solid state reaction method. X-ray diffraction analysis shows that the lattice parameters of Ca1−xSrxFe2As2 decrease continuously with increasing Ca content. Resistivity measurements reveal that the Ca/Sr ratio has a visible influence on the resistivity anomaly associated with the spin-density-wave (SDW) instability. Experimental measurements on Ca0.5Sr0.5Fe2−yCoyAs2 show clear superconducting transitions for Co in range of 0.26≤y≤0.43; the highest critical transition temperature is found to be at about 17 K. Transmission electron microscopy (TEM) investigations on the superconducting Ca0.5Sr0.5Fe2−yCoyAs2 samples reveal visible inhomogeneous distribution of Sr and Ca elements, which could result in structural distortions and broaden superconducting transitions as observed in our experiments.