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.

The growth of REBa2Cu3O7-δ (REBCOZrare earth elements) high-temperature superconducting thick films by liquid phase epitaxy is reviewed, which are most promising for electronic device and coated conductor applications. The paper focused on thermodynamic relations, chemical reactions and physical phenomena in the liquid phase epitaxy process, which are closely related to the control of the microstructures and properties of materials. Recent progresses achieved and the problems to be solved have been reviewed in above sections.

Using YBCO/MgO thin films, for the first time, we report a success in the melt-textured growth of YBCO bulks by the cold-seeding method. The grown bulk has a good orientation relation of YBCO 〈100〉 bulk Ⅱ YBCO 〈100〉 film Ⅱ MgO 〈100〉 substrate. In this process, the YBCO film withstood heating over its peritectic temperature (up to 1045℃) for 1.5 h and acted as a seed for the YBCO bulk growth, indicating an intrinsic superheating property, which was reported in other work. The unique superheating mechanism in this study was clarified. It was found that the a-b alignment of YBCO film plays a key role in controlling the single grain growth of YBCO bulk.

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.

Abrupt transition from a-axis growth to c-axis growth was found in the liquid phase epitaxy LPE process of YBa2Cu3Ox YBCO or Y123 on 110 NdGaO3 substrate. Subsequently, the influence of supersaturation and liquid composition on the orientation of LPE thick films was systematically studied. Dissimilar to the thin film deposition, the a-phase growth was predominant at a low supersaturation about 17K, especially grown by using a Cu-rich melt. The investigation of the initial stage of YBCO growth was performed, in which we found the protruding epitaxial a-axis grains and preferentially a-phase nucleation on the c-dominated thick film. The energy dispersive x-ray spectrometry attached scanning electron microscope was employed to confirm the composition of the outgrowth of long-axis grains, as well as the microstructure around the dipping boundary line in the initial growth. Based on the "nucleation and growth" mode, a comprehensive description of the competition between a-axis and c-axis growth under various growth environments was given, which further unveiled the origin of a-c transition in YBCO thick films.