Large REBCO single crystals: growth processes and superconducting properties

Abstract

A low solubility of yttrium in the Ba - Cu - O melt and a steep liquidus slope near the peritectic temperature lead to a very slow growth rate of (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 (NdBCO) single crystals with an edge size over 25 mm in the a - b plane and up to 20 mm 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 of 92.7 K was achieved from a Y123 single crystal grown under 1 atm oxygen partial pressure, indicating that is insensitive to the oxygen pressure of the growth atmosphere in the YBCO system. A high 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 . By partial substitution of Sm at the Y sites up to 30%, (Y(Sm)BCO) crystals show a of and do not display depression.

Growth condition related orientation transition for YBa2Cu3O7−δ films on NdGaO3 substrate

“…At high temperatures, owing to the NGO etch-back, the system changes from YBCO to Nd-YBCO and the effective s instantly increases as the substrate is dipped into solution. Similarly to the SmBCO system, NdBCO has a gradual slope of its liquidus, and the growth window of a-axis films is proved to be quite small [3,[28][29]. Both the enhancement of the effective s and the system shift to Nd-YBCO, facilitate the growth of c-axis phase.…”

Critical temperature of LaBa2Cu3Oy thin films by vapor–liquid–solid growth technique improved by the composition ratio in liquid phase

“…It is reported that T c of REBCO single crystals are improved with increasing Ba/Cu ratio in growth flux and suppressing the RE/Ba substitution [13][14][15]. Based on these facts, we examined the effects of Ba/Cu ratio in growth flux on R-T and T c .…”

“…We consider that the reasons are the stability of the liquid layer, oxygen vacancies and La/Ba substitution. In the case of top-seeded solution growth (TSSG) method presented to suppress a RE/Ba substitution, a growth flux composition relates with RE/Ba substitution [13][14][15], so that the REBCO single crystal exhibited a high T c by controlling Ba/Cu ratio in the growth flux.…”

Peritectic melting of thin films, superheating and applications in growth of REBCO superconductors

“…However, for the YBCO system, it cannot produce sufficiently large crystals due to its low growth rate and small growth window. Although by Top-seeded solution growth (TSSG), high quality YBCO single crystals with large sizes can be obtained, however, the growth rate is limited by a low solubility of Y element in the Ba-Cu-O solvent [130][131][132]. Recently, Babu et al [133] and Wang et al [134] reported a modified TSMG, in which a single phase of Y123 as a precursor material was used, instead of the conventional Y123 + Y211.…”