Study in a new fabrication method of BaTiO_3 single crystal

为了探索一种制备BaTiO_3单晶的新方法，我们研究了添加TiO_2的BaTiO_3陶瓷不发生二次再结晶的条件。当样品在共晶点以上烧结时，通过使用平均粒度较大的低活性BaTiO_3粉末，证明了作为二次再结晶抑制剂的TiO_2在这些条件下的作用显著。在此条件下，随着二氧化钛加入量的增加，生成液相的量增加。二次再结晶与生成的液相量和烧结温度有关。由于BaTiO_3在晶间的扩散很少，抑制了晶粒的快速长大，即二次再结晶，用共晶点附近电导率的变化程度来估计相量。电导率改变了…在未掺杂的样品中，这种变化更为缓慢。另一方面，在添加了二氧化钛的样品中，电导率在共晶点附近发生了显著的变化，并随着二氧化钛加入量的增加而成比例地增加，即产生的液体相。因此，测量共晶点附近的电导率是确定热处理过程中液相量的一种有效方法。在不发生二次再结晶的条件下，对含有晶种的多晶体进行热处理以使晶种生长。晶种向四面八方生长，不含二次再结晶颗粒。在这种制备方法中，溶液再沉淀过程是主要的生长机制。单晶的生长是由于晶种和多晶体颗粒之间的溶解度不同造成的。镶嵌在多晶体中的晶种的生长速度随生成液相量的减少和热处理温度的升高而增加。多孔多晶区的孔洞被结合到生长的单晶中。然而，单晶的生长部分表现出相似的性质，如相对介电常数和晶格常数的温度依赖性。因此，通过去除多孔多晶体上的气孔，可以制备出高质量的BaTiO_3单晶。较少

We investigated the conditions in which no secondary recrystallization occurred in TiO_2 added BaTiO_3 ceramics for a new fabrication method of BaTiO_3 single crystal. These conditions were confirmed when the specimens were sintered above the eutectic point, The effect of TiO_2 as a secondary recrystallization inhibitor worked on these conditions remarkably by using a low reactive BaTiO_3 powder that have a comparatively large average grain size. In these conditions, the increase of added TiO_2 gave rise to the increase of amount of generated liquid phase. The secondary recrystallization depended on the amount of generated liquid phase and the sintering temperature. Owing to little amount of diffusion of BaTiO_3 in the liquid phase existing between grains, the rapid grain growth, namely, the secondary recrystallization was restrained.The amount of liquid phase was estimated as the degree of change in electrical conductivity around the eutectic point. The electrical conductivity changed … More gradually in the undoped specimen. On the other hand, a striking change of electrical conductivity occurred around the eutectic point in TiO_2 added specimens, proportionally increasing with the amount of added TiO_1, namely, the generated liquid phase. Accordingly, it was found that the measurement of electrical conductivity around the eutectic point was an effective way to determine the amount of liquid phase during heat treatment.A polycrystalline body that contained a seed crystal was heat-treated to make the seed crystal grow using the above conditions in which no secondary recrystallization occurred. The seed crystal grew in all directions without containing the secondary recrystallized grain. The solution-reprecipitation process was the dominant growth mechanism in this fabrication method. The growth of single crystal was caused by a difference of solubility between the seed crystal and the grains of polycrystalline body. The growth rate of seed crystal embedded in the polycrystalline body increased with decreasing the amount of generated liquid phase and increasing of heat-treating temperature. Pores in the porous polycrystalline area were incorporated into the grown single crystal. However, the growth part of single crystal exhibited similar properties, such as the temperature dependence of relative dielectric constant and the lattice constant. Therefore, a high qualitative BaTiO_3 single crystal might be fabricated by removing pores from the porous polycrystalline body. Less