Study on Ordering of Ba(Mg1/3Ta2/3)O3 Single Crystal

• Main Authors: LEE YOU CHANG, 李友彰
• Other Authors: 蔡大翔
• Format: Others
• Language: zh-TW
• Published: 2000
• Online Access: http://ndltd.ncl.edu.tw/handle/71756619500816573204

碩士 === 國立臺灣科技大學 === 化學工程系 === 88 === Ordered structure of Ba(Mg1/3Ta2/3)O3 BMT has been investigated in the single crystal of BMT, synthesized in the BaF2 melt flux at 1400℃. The as-grown crystals are of disordered perovskite phase, shown in both of X-ray diffraction and electron diffraction. Its ordered structure gradually establishes in the 1500℃ annealing, as evidenced in the increasing intensities of superstructure X-ray reflections with annealing time. Meanwhile the half-height width of 1/2(111)c reflection decreases with annealing time, indicating that the ordered domain size increases with annealing time. The electron diffraction patterns of 1500℃-annealed specimen reveal finer details on the local ordered structure. Hazy, diffuse reflections have been found between the clear fundamental perovskite in the 1500℃-annealed specimen. These diffuse reflections persist after 24-hour 1500℃annealing, and they turn into sharp reflection spots when the annealing temperature is raised to 1600℃. The electron diffraction intensities recorded on image plates further reveal that the location of diffuse reflections shift away from their regular positions toward the center. Hence the feature of 1:2 ordered phase looks more like 1:1 ordered phase when the diffuse superstructure reflections are present. While the hazy diffuse reflections can be attributed to the less perfect ordered structure formed in the early stage, the shifting toward center position remains a puzzle, which needs further study. The HRTEM images show that 1600℃-annealed specimen have very large ordered domains of one variant. On the other hand, the HRTEM images of 1500℃-annealed specimen exhibit uncertain 1:2 ordering contrast in a very small region. The small domain size in the early stage could be the reason why the contrast feature of 1:2 ordering fail to show up.