Study in a new fabrication method of BaTiO_3 single crystal

研究了在TiO_2中添加BaTiO_3的陶瓷在不发生二次再结晶的条件下，制备BaTiO_3单晶的新方法。当试样在共晶点以上烧结时，这些条件得到了证实。在这些条件下，TiO_2作为二次再结晶抑制剂的效果显著，使用的是平均晶粒尺寸较大的低活性BaTiO_3粉末。在此条件下，TiO_2添加量的增加导致液相生成量的增加。二次再结晶主要受液相生成量和烧结温度的影响。由于BaTiO_3在液相中存在少量的扩散，抑制了晶粒的快速生长，即二次再结晶。液相的量由共晶点周围电导率的变化程度来估计。在未掺杂的样品中，电导率的变化更为缓慢。另一方面，加入TiO_2的试样在共晶点附近的电导率发生了显著的变化，随着TiO_1（即生成的液相）的加入量的增加，电导率呈比例增加。因此，发现测量共晶点周围的电导率是确定热处理过程中液相量的有效方法。对含有种子晶体的多晶体进行热处理，使种子晶体在不发生二次再结晶的条件下生长。种子晶向各个方向生长，不含二次再结晶晶粒。溶液-再沉淀过程是该制备方法中主要的生长机制。单晶的生长是由种子晶与多晶体晶粒溶解度的差异引起的。随着液相生成量的减少和热处理温度的升高，嵌入多晶体中的晶种生长速率增大。多孔多晶区的孔隙被纳入生长的单晶中。而单晶的生长部分表现出类似的性质，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孔隙，可以制备出高质量的BaTiO_3单晶。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