Abstract
Single crystals of high-temperature superconductor YBa2Cu3Ox have successfully been prepared using a CuO or a BaO-CuO flux method. Several shapes of crystals are obtained in a single batch. Two types of crystals having the same YBa2Cu3Ox composition are foud: one is thin plates which are semiconductive but not superconductine above 4.2K, and another shows a very sharp superconducting transition above 90K in the as-grown state. The former is supposed to form under a solution growth condition, whereas the latter by the use of a peritectic reaction between Y2BaCuO5 and surrounding liquid phase. As the former is extremely thin whereas the latter is thick, a large volume of block crystals can possibly be obtained in the latter reaction. For the purpose of obtaining crystals of higher quality, an experiment was held at various growth-temperatures and compositions of flux. As a result, growth temperature should be set at a little higher than the peritectic temperature. If the max. temperature is too high, the separation of Y2BaCuO5 from the co-existing liquid phase occurs because of the coagulation of the liquid at high temperatures, and this separation prevents the progress of the peritectic reaction. An application of CuO-BaO flux in the place of pure CuO effectively prevents the crystals from taking in flux. Due to the low melting point, CuO-BaO flux can easily be discharged from the crystals and the strong impetus to advance the peritectic reaction.
