Temperature-composition phase diagrams for Ba1-xSrxFe2As2 (0 ≤ x ≤ 1) and superconducting Ba0.5Sr0.5(Fe1-yCoy)2As2 (0 ≤ y ≤ 0.141)

Single crystals of mixed alkaline earth metal iron arsenide materials, Ba1-xSrxFe2As2 with 0.185 <= x <= 0.762 and Ba0.5Sr0.5(Fe1-yCoy)(2)As-2 with 0.028 <= y <= 0.141, are synthesized via the self-flux method. Ba1-xSrxFe2As2 display spin-density wave features (T-N) at temperatures intermediate to the parent materials, x = 0 and 1, with T-N(x) following an approximately linear trend. Cobalt doping of the 1:1 Ba:Sr mixture, Ba0.5Sr0.5(Fe1-yCoy)(2)As-2, results in a superconducting dome with maximum transition temperature of T-C = 19 K at y = 0.092, close to the maximum transition temperatures observed in unmixed A(Fe1-yCoy)(2)As-2; however, an annealed crystal with y = 0.141 showed a T-C increase from 11 to 16 K with a decrease in Sommerfeld coefficient gamma from 2.58(2) to 0.63(2) mJ/(K-2 mol atom). For the underdoped y = 0.053, neutron diffraction results give evidence that T-N and structural transition (T-O) are linked at 78 K, with anomalies observed in magnetization, resistivity, and heat capacity data, while a superconducting transition at T-C approximate to 6 K is seen in resistivity and heat capacity data. Scanning tunneling microscopy measurements for y = 0.073 give Dynes broadening factor Gamma = 1.15 and a superconducting gap Lambda = 2.37 meV with evidence of surface inhomogeneity.