Growth of single crystalline films of bismuth based oxide superconductors by the liquid phase epitaxy method

研究了以KCl为溶剂，液相外延生长Bi2212超导薄膜在衬底晶体上的生长条件，在初始成分为Bi: Sr: Ca: Cu= 2:2:1: 2的情况下，最佳生长温度为840 ~ 870偶联温度。在此条件下，衬底上仅生长2212相薄膜。早期生长机制为岛状生长，后来转变为连续膜状生长模式。当岛屿在基材上相遇时，会发生较大的台阶，这使得薄膜平整度很差。然而，当我们使用LaAlO3（110）衬底时，生长的2201薄膜显示出几微米见方的原子平面面积。当我们使用NdGaO_3 *(001)衬底时，得到了接近双晶的自由薄膜。用高温光学显微镜原位观察了Bi-Sr-Ca-Cu-O氧化物体系的溶解和凝固过程。我们可以确定铋基氧化物超导体体系自通量生长的初晶场（晶体作为第一固体生长的温度和成分的粗略区域）。我们确定这一地区的铋含量比以往报道的要高。在初次结晶领域知识的基础上，应用了流动溶剂浮区法。为了在结晶学c轴方向上获得单晶厚度，需要通过播种等方式控制成核。利用种子晶体，我们成功地从种子晶体开始连续生长，这表明我们确定的初级结晶场是可靠和有用的。关于一次结晶场的下一个课题是明确区分2212相和2201相区域。我们尝试了使用自磁通的液相外延法，但失败了。熔剂对基片的腐蚀使我们得到了单膜晶体。需要进一步的研究。

Growth conditions of Bi2212 superconducting films on the substrate crystal by the liquid phase epitaxial growth method using KCl as a solvent were investigated, In the case of the starting composition of Bi : Sr : Ca : Cu=2 : 2 : 1 : 2, the best growth temperature ranged from 840 to 870ﾟC.Under this condition, only the 2212 phase film grew on the substrate. In the early stage, the growth mechanism was the island growth and the changed to the continuous film growth mode. When islands met on the substrate, large steps occurred and this made film flattness poor. When we used the LaAlO3(1 10) substrate, however, grown 2201 films showed atomically flat area extending few micrometers square. When we used the NdGaO_3 * (001) substrate, nearly twin free film was obtained.Dessolution and solidification process of the oxide system of Bi-Sr-Ca-Cu-O was in situ observed with high temperature optical microscopy. We could determined the primary crystallization field (rough region of temperature and composition where the crystals grow as the first solid) for the self flux growth of the Bi based oxide superconductors system. This region we determined contained much bismuth than those ever reported. Traveling solvent floating zone method was applied on the basis of the knowledge of the primary crystallization field. To obtain single crystals thick in the crystallographic c-axis direction, the control of the nucleation by such as seeding was found to be needed. Using the seed crystal, we succeeded in continuous growth from the seed crystal and this indicated that the primary crystallization field we determined was reliable and useful. Next subject on the primary crystallization field is to clearly separate the 2212 phase and the 2201 phase region. We tried the liquid phase epitaxial method using the self flux, to fail. Corrosion of the substrates by the flux enabled us to obtaine the single film crystal. Further study is needed.