Effect of oxygen partial pressure on grain boundary structure and grain growth behavior in BaTiO3

The structural transition of grain boundaries in BaTiO3 and related grain growth behaviors have been investigated for a wide range of oxygen partial pressures (PO2)(PO2). A correlation among PO2PO2, grain boundary structure and grain growth behavior has been found. At PO2=0.2atm, all of the grain boundaries were faceted and abnormal grain growth occurred with the assistance of {1 1 1} twins as in previous investigations. As PO2PO2 decreased below 10−11 atm the formation of {1 1 1} twins was inhibited. At a moderately low PO2PO2 between 10−11 and 10−17 atm, grain growth was suppressed, although a small fraction, less than 10%, of the boundary was rough. With an increased fraction of rough boundaries on reduction of PO2PO2 to 4 × 10−18 atm, abnormal grain growth was observed for the first time in the absence of {1 1 1} twins in BaTiO3. Further increases in the rough fraction to ∼80% changed the growth behavior to normal. These observations show that in BaTiO3, a variety of growth behaviors can result with reduction of PO2PO2: from abnormal with the assistance of {1 1 1} twins, stagnant without {1 1 1} twins, abnormal again without {1 1 1} twins to normal without {1 1 1} twins. The observed difference in growth behavior with PO2PO2 and grain boundary structure has been explained in terms of the change in step free energy and the critical driving force for appreciable migration of the boundary.