Development of a New Crystal Growth Technique using Preitectic Reactions

包晶反应通常是在不一致的熔融液体凝固时观察到的，它被应用于生长大的氧化物晶体。Ostwald熟化机制下的再结晶是在包晶固液共存的包晶条件下进行的。具有包晶层的小颗粒由于具有较高的表面自由能而倾向于分解到熔体中，而被无限曲率的发达表面包围的大的、生长良好的晶体变大。使用该技术的优点是，具有高熔点、高汽化或熔点不一致的材料可以结晶，生长过程与通常的助熔剂方法一样简单，并且由于生长温度低，可以避免来自坩埚材料的不必要的污染。在这里，我们将这一技术应用于氧化物超导体和低维氧化物等氧化物中，成功地生长了YBa2Cu3Ox、Tl2Ba2Ca2Cu3O&lt；10、Tl2Ba5Cu4O&lt；x、&gt；SrCuO2、Y2Cu2O5、CuFeO2、PdCoO2、PtCoO2和MgSiO_3等毫米级高质量晶体，并用这些晶体测量了晶体结构、磁学和电学性质。为了更准确地阐明生长机制，我们搭建了一台高温X射线衍射仪和快速计数系统，用于分析包晶条件下的相变率。结果表明，液相中的扩散不是固相扩散，而是速率控制过程。在1273K和室温下，在相同的空气中，还建立了Bi一sr-CuO，Bi一sr-Ca一Cu一O和BiPb一sr一Ca一Cu一O三元系的详细的相关系。

Peritectic reactions which are commonly observed upon solidification of incongently molten liquid have been applied for growth of large oxide crystals. Recrystallization under the Ostwald ripening mechanism proceeded in keeping of such a peritectic condition where peritectic solids coexisted with liquid. Small particles with peritectic layrs tended to diminish by resolution into the melt due to high surface free energies and large, well-habited crystals surrounded by developed surfaces with infinit curvatures became large. The merits of using this technique are that materials with high melting, high vaporizing or incongruent melting properties can be crystallized, that the growth procedure is so simple as usual flux methods and that undesired contamination from crucible materials can be avoided because of low growth temperatures. Here we applied this technique to oxides such as oxide superconductors and low dimensional oxides, and succeeded in growing mm-sized, high quality crystals of YBa_2Cu_3O_x, Tl_2Ba_2Ca_2Cu_3O_<10>, Tl_2Ba_5Cu_4O_<x, > SrCuO_2, Y_2Cu_2O_5, CuFeO_2, PdCoO_2 PtCoO_2 and MgSiO_3. Using these crystals, we measured the crystal structures, magnetic and electric properties. To clarify the growth mechanism more precisely, we have constracted a high temperature X-ray diffraction apparatus with a rapid counting system for analyzing the phase change rates in peritectic conditions. The results indicated that the diffusion in the liquid phase was the rate determining process rather than in the soild phase. Detailed phase relations in the Bi-Sr-Cu-O,Bi-Sr-Ca-Cu-O and Bi-Pb-Sr-Ca-Cu-O systems have been also established between 1273K and room temperature using the same spparatus in air.