Crystal Growth and Characterization of FeAs-Based Superconductors
FeAs-based single crystals of Ba1-xKxFe2As2 and Sr1-xKxFe2As2 were grown in a Mo capsule at the temperatures from 1200oC down to 850oC by a FeAs-self-flux method. Most of their sizes were approximately 0.2-0.5 mm. A larger single crystal of Sr Fe2As2 about 7mm in diameter was obtained by the same procedure, as appeared in a round-shape. Most of the time, potassium-doped crystals tends to be smaller than undoped ones. An example of Tc for a Ba1-xKxFe2As2 single crystal measured with a SQUID magnetometer, which indicates Tc at 38 K. Tc s are sometimes lower dependent on the potassium composition. The substitution reaction between SrFe2As2 and potassium was examined. An undoped crystal absorbed potassium at around 600oC and showed superconductivity by the reaction.
T. Chandra, N. Wanderka, W. Reimers , M. Ionescu
H. Takeya et al., "Crystal Growth and Characterization of FeAs-Based Superconductors", Materials Science Forum, Vols. 638-642, pp. 1412-1415, 2010