Interface structure dependent step free energy and grain growth behavior of core/shell grains in (Y, Mg)-doped BaTiO3 containing a liquid phase

The grain growth behavior of 92BaTiO3-3Y2O3-3MgO-2SiO2 (mol.%) containing a liquid phase has been systematically investigated with respect to oxygen partial pressure (PO2). Bi-layer samples, where a pre-sintered polycrystalline sample is coupled with a single crystal of pure BaTiO3, were heat-treated under an atmosphere ranging from wet H2 (PO2~ 10−13-10−14 atm) to air (PO2~ 0.2 atm) simulating industrial conditions. The single crystal provided a significantly larger driving force for grain growth than matrix grains, permitting an elaborate analysis. Considering the bi-layer sample as a single system, a clear shift of grain growth behavior was observed: (pseudo) normal grain growth (NGG), delayed abnormal grain growth (AGG), and stagnant grain growth (SGG), as the atmosphere became more oxidizing. The shift was accompanied by structural change of solid/liquid interfaces and grain boundaries and successfully explained by the step free energy effect, emphasizing the validity of interface control in BaTiO3 with a solid/liquid interface.