The REBCO (RE=Sm, Nd) single crystals used in fundamental research especially in the melt texture growth of bulk superconductor. Because of complicated stoichiometry and difference evaporation temperatures of the metal ions in the precursor, high temperature superconductor single crystals commonly grown by the self-flux method. In this work, we describe the fabrication method of YBCO and SmBCO single crystal superconductor for investigating superconducting properties and their crystal structure. In order to obtain high quality REBCO single crystal by flux method several parameters are important. These parameters are as follows: Composition of the flux, type of crucible material, temperature profile of single crystal growth treatment and crystal nucleation process conditions in the flux. REBCO, as the solute part of the crystal growth route by flux method, was prepared from the chemical reagents of RE2O3, BaCO3 and CuO with a molar ratio of 1:2:3 which were mixed mechanically by a ball mill and then performing the calcination process at 920 °C twice. BaCO3 and CuO were used as flux agent with the molar ratio of Ba:Cu=28:72. In order to proceed with the crystal growth rote, REBCO and the flux were mix again with the amount of 10 wt% and 90wt% respectively. The Mixture was then calcinated at 910 °C in Al2O3 crucible. The XRD results showed the existence of three phases of BaCuO2, CuO and REBa2Cu3O7 simultaneously in the sample. An especial design performed in the tube furnace in order to deliver and guided the cold air to the vicinity of the crucible for performing a gradient temperature for the crystal growth process. Apart from that for growing larger single crystal a unique heat treatment were also applied. The temperature in growth step is lowered at a different rate of 0.2–1.0 °C/h. Size of as-grown single crystals increased as the rate was decreased. The flux removes from the crucible at 950 °C. By this method, free standing single crystals larger than 2×2×0.5mm3 could be achieved. X ray diffraction pattern had an extremely sharp peaks that shown high degree of crystallinity. Single crystals annealed at 860–900 °C in flowing of oxygen atmosphere for 24 h. Critical temperature of single crystals YBCO and SmBCO were found 89 and 85k respectively using standard four probe technique. Decrease of the critical temperature may be associated with the Al Impurities from crucible.

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