The effects of oxygen partial pressure on Y123 single-crystal growth, morphology and properties were inves-tigated. YBCO (Y123) single crystals were fabricated using the crystal pulling method under 1 atm partial pressure played a significant role in increasing growth rate, which was 1.5-2.5 times higher than that of crystals fabricated under air atmosphere. A large crystal with size of 19.8

A low solubility of yttrium in the Ba-Cu-O melt and a steep liquidus slope near the peritectic temperature Tp lead to a very slow growth rate of YBa2Cu3O7-δ(YBCO or Y123) single crystals and this creates a problem in growth of large single crystals. To solve this problem, increasing the growth rate and extending the growth time are significant. Using the crystal pulling method, we have developed several processes and succeeded in growing large Y123 and Nd1−χBa2+χCu3O7−(NδBCO) single crystals with an edge size over 25mm in the a-b plane and up to 20mm in the c-axis direction. In this article, three methods of increasing growth rate are reviewed. They are (i) employing high oxygen partial pressure, (ii) choosing RE (rare earth) elements with higher solubilities in the Ba-Cu-O solution, and (iii) growing REBCO crystals including several RE elements. Using these methods the growth rate was effectively enhanced from two to five times that of Y123. The critical temperature Tc of 92.7 K was achieved from a Y123 single crystal grown under 1 atm oxygen partial pressure, indicating that Tc is insensitive to the oxygen pressure of the growth atmosphere in the YBCO system. A high Tc of about 95 K for NdBCO superconductors with a sharp transition was obtained by controlling the ratio of Ba to Cu (Ba/Cu) in the liquid, suggesting that the Ba/Cu ratio in the liquid composition has a significant importance in controlling Tc. By partial substitution of Sm at the Y sites up to 30%, Y1−xSmx Ba2Cu3O7−(Y(Sm)BCO) crystals show a Tc of 91±1K and do not display Tc depression.

YBa2Cu3O7-dδ (YBCO) thin films were used as seed films for growing high peritectic temperature (TP) Nd1+χBa2-χCu3O7-δ (NdBCO) thick films by liquid phase epitaxy. On heating to a temperature above TP; polycrystalline YBCO grains agglomerate and then partially decompose. The metastable YBCO phase takes the lowest energy configuration, an enlarged size and a shape with an equilibrium curvature, which prohibits them from immediate decomposition and dissolution. As a result, the retained YBCO grains act as heteroeptaxial-seeds for the growing NdBCO grains in the Nd-Ba-Cu-O solution. Yttrium was detected in the NdBCO grains grown in the initial stage by EPMA, strongly supporting a model of the YBCO-seeded NdBCO growth.

We report a novel-superheating phenomenon inYBa2Cu3Oz (Y123) oxide films (over 45K), whichwere prepared by vapour deposition onMgOsubstrates. The origin of this superheating could be mainly attributed to the positive change of surface energy in peritectic melting, during which Y123 melts into the Y2BaCuO5 (Y211) solid and the Ba-Cu-O liquid. It was found that the heterogeneous melting initiates at the Y123/MgO interface and the molten liquid does not wet MgO and Y123. These melting features of Y123 films explain the delaying of the melting process.

In this communication, for the first time, we report on a high-Tc 95K Sm1+xBa2−xCu3Oz (SmBCO) single crystal with a small transition width of less than 0.5K grown under 1 atm oxygen pressure. We found that the substitution of Ba by Sm could be effectively suppressed by using liquid composition control. Jc-B curves and scaling analysis of samples at 77K with B Ⅱ c indicate that a delta Tc style defect is the predominant pinning in SmBCO crystals.