The present investigation studies the solid/liquid interface structure between $BaTiO_3$ and a $SiO_2$ -rich liquid with atmosphere and its effect on the microstructure. A (100) $BaTiO_3$ single crystal was embedded in a $5mole%-SiO_2-excess$ $BaTiO_3$ powder compact and sintered at 1280 ℃ under various oxygen partial pressures $(0.2 atm ~ 10^{-24} atm)$. During sintering, the single crystal grew into the fine matrix and trapped isolated liquid. The shape of the entrapped negative crystal was rounded i.e. interfacial step free energy decreased as the oxygen partial pressure decreased. The microstructural evolution of $10 mole%-SiO_2-excess BaTiO_3$ at 1280 ℃ was also observed under various oxygen partial pressures by optical microscope (OM), scanning electron microscope (SEM) and transmission electron microscope(TEM). The grain growth mode changed dramatically with the interface structure from stagnant, abnormal, to normal. In the case of stagnant grain growth, apparent growth exponent was about 110 in contrast to 3 for normal grain growth in a reducing atmosphere. An intergranular liquid film was observed between the fine matrix grains. Abnormal grain growth was observed in a specimen sintered under an intermediate atmosphere $(P_{O2}~10^{-20} atm)$ as at an increased temperature of 1300 ℃.
The observed grain growth behavior was explained in terms of the step free energy of the interface and the driving force for grain growth. Stagnant grain growth is believed to occur when the step free energy is very large so that the critical driving force is larger than the driving force for the growth of the lager grain. On the other hand, stagnant and abnormal grain growth can occur when the driving force is comparable to the critical driving force. Normal grain growth occurs when the driving force for grain growth is larger than the critical driving force.
$SiO_2$ 액상이 게재된 $BaTiO_3$ 의 분위기에따른 고/액 꼐면의 모양변화와 그에 따른 입성장 양상을 연구하였다. (100) $BaTiO_3$ 단결정을 이용하여 액상이 포획된 음결정의 분위기에 따른 모양변화를 관찰한 결과, 환원 분위기로 진행됨에 따라 고/액 계면이 둥글어 짐을 확인할 수 있었고, 이로 분위기에 따른 step free energy의 변화를 유추해 볼 수 있었다. 입성장 양상은 분위기에 따라 매우 독특하게 변화하였는데 공기 중에서 소결한 시편에서는 입성장이 거의 발생하지 않았고, 환원 분위기에서는 정상입성장이 발생하였으며, 그 중간 분위기에서는 비정상 입자 성장이 일어났다. 이는 이차핵생성/성장의 임계자유에너지가 분위기에 따라 감소함에 따른 변화라 생각된다.
