Step free energy change and microstructural development in BaTiO3-SiO2

The effect of step free energy on the grain growth behavior in a liquid matrix is studied in a model system BaTiO3-SiO2. BaTiO3-10SiO(2) (mole %) powder compacts were sintered at 1280 degrees C under various oxygen partial pressures (P-O2), 0.2, similar to 10(-17) and similar to 10(-24) atm. As the step free energy decreases with the reduction of P-O2, it was possible to observe the change in growth behavior with the reduction of the step free energy. At P-O2=0.2 atm, essentially no grain growth (stagnant grain growth) occurred during sintering up to 50 h. At P-O2 approximate to 10(-17) atm, abnormal grain growth followed stagnant grain growth during extended sintering (incubation of abnormal grain growth). At P-O2 approximate to 10(-24) atm, normal grain growth occurred. These changes in growth behavior with P-O2 and the step free energy reduction are explained in terms of the change in the critical driving force for appreciable growth relative to the maximum driving force for grain growth. The present experimental results provide an example of microstructure control in solid-liquid two-phase systems via step free energy change.