Process for high growth rate and high superconducting properties of REBCO single crystals

Process developments for both higher growth rate and superconducting properties are two main objectives of RE1Ba2Cu3O7-δ (REBCO or RE123) single crystal growth. In this paper, we will review several processes for increasing growth rate and achieving higher Tc REBCO superconductors. There are two effective methods to enhance the growth rate. One is to grow single crystals under high oxygen partial pressure, the other is to partially or completely replace Y by RE elements with higher solubilities in the Ba-Cu-O solution, for instance RE = Nd, Sm. Using these methods the growth rate was increased. The unprecendently large REBCO single crystals with the size 25 × 25 mm2 on the a-b plane and up to 20 mm in thickness were obtained. Regarding superconductivity, the critical temperature Tc of about 93 K was achieved from the Y123 single crystals both grown under air and 1 atm oxygen pressure, indicating that Tc is insensitive to the growth atmosphere of the oxygen pressure in the YBCO system. Furthermore, the high Tc of about 95 K NdBCO superconductors with a sharp transition was obtained by using Ba-rich liquid (Ba:Cu ratio = 0.75–0.80 of solvent), suggesting that the liquid composition is an important thermodynamic parameter for controlling Tc. Moreover, the partial substitution RE (RE = Nd, Sm) at the Y sites up to 30% shows no obvious reduction of Tc remaining at about 91±1 K.