High-pressure growth of fluorine-free SmFeAsO$_{1-x}$ superconducting   single crystals
  Superconducting single crystals of SmFeAsO$_{1-x}$ without fluorine doping were grown at a pressure of 3.3 GPa and a temperature of 1350-1450 $^\circ$C by using the self-flux method. Plate-like single crystals of a few-150 $\mu$m in their lateral size were obtained. Single crystals showed the superconducting transition at about 53.5 K with a narrow transition width of 0.5 K. The synchrotron-irradiated x-ray diffractometry patterns and high-angle-annular-dark-field scanning transmission electron microscopy images point to the high quality of the crystals with a well-defined layered tetragonal structure. The chemical compositions of the crystals were estimated by using the electron-probe x-ray microanalysis. 
Hyun-Sook Lee, Jae-Hyun Park, Jae-Yeap Lee, Nak-Heon Sung, Ju-Young   Kim, B. K. Cho, Tae-Yeong Koo, Chang-Uk Jung, and Hu-J...