DESIGN OF CERAMICS BY COTROLLING GRAIN BOUNDARY CHARACTER AND QUANTUM STRUCTURES

研究了双晶和三晶氧化陶瓷的晶界特性对陶瓷性能的影响。系统制备了Al_2O_3、ZrO_2、ZnO和SrTiO_3的双晶，并用HREM、EELS和EDS对其晶界原子结构、化学键态和组成进行了表征。测量了两种双晶的晶界能、蠕变行为和电子性能，并从晶界特征的角度阐明了两种双晶的晶界结构、化学性质和性能之间的关系。采用HREM和静态晶格计算相结合的方法分析了各双晶的晶界结构。HRTEM观察发现，晶界沿晶界面有平移的不对称结构。静态点阵计算得到的最稳定的晶界模型与HREM图像吻合较好。发现晶界面的特征是决定晶界原子结构的重要因素。通过高温压缩蠕变试验研究了合金的晶界滑动行为。发现晶界滑动引起的蠕变行为取决于晶界结构和原子密度[0001]。纯氧化铝的倾斜晶界沿晶界面含有较大的开放空间。掺Y的氧化铝晶界也表现出类似的核结构，这表明即使在原子水平上，Y离子偏析也没有改变晶界结构。此外，静态晶格计算表明，Y离子倾向于位于晶界核的开放空间周围。因此，我们认为即使Y离子的浓度很小，也会降低开晶界核处的原子扩散率。基于上述结果，定量地认识了晶界原子结构和性质的重要性，并提出了陶瓷晶界设计的指导方针。少

The effect of grain boundary character on the properties in oxide ceramics by using bicrystals and tricrystals. The bicrystals of Al_2O_3,ZrO_2,ZnO and SrTiO_3 have systematically fabricated, and the grain boundary atomic structures, chemical bonding state and composition were characterized by HREM, EELS and EDS. In addition, the grain boundary energy, creep behavior and electronic properties in the respective bicrystals were measured, and the relationships of grain boundary structures, chemistry and properties were clarified from the view point of grain boundary character. The grain boundary structures in the respective bicrystals were thus analyzed by combination of HREM and static lattice calculation. HRTEM observation revealed that the present grain boundaries have asymmetrical structures with translation along the grain boundary plane. The most stable grain boundary models calculated by static lattice calculation well correspond with the HREM image. It was found that characters of … More grain boundary plane are an important factor to determine grain boundary atomic structures. The behavior of grain boundary sliding was also investigated by high temperature compressive creep test. The creep behavior due to grain boundary sliding was found to depend on the grain boundary structures and atomic density The [0001] tilt grain boundaries in pure alumina contained large open spaces along the boundary plane. The Y-doped boundary in alumina also exhibited a similar core structure, indicating that Y ions segregation did not change the grain boundary structure even at the atomic level. In addition, static lattice calculations showed that Y ions tended to be located around the open spaces at the grain boundary core. Therefore, it is thought that Y ions play a role for decreasing atomic diffusivity at the open grain boundary core even when their concentration is quite small. Based on the results mentioned above, importance of grain boundary atomic structures and characters were quantitatively understood, and an guideline to design ceramic grain boundary were proposed in this study. Less