Effects of donor concentration and oxygen partial pressure on interface morphology and grain growth behavior in SrTiO 3

Abstract

Change in interface morphology with ionic vacancy concentration and the correlation between interface structure and grain growth behavior in strontium titanate (SrTiO 3) have been investigated using SrTiO 3 single crystals and powder compacts. Under experimental conditions where SrTiO 3 contains a negligible amount of ionic vacancies, the shape of the single crystal embedded in matrix grains was well faceted, showing a strong anisotropy in interfacial energy. However, as strontium or oxygen vacancies increased with the addition of an Nb 2O 5 donor dopant or reduction of oxygen partial pressure, the faceted shape changed to a smoothly curved rough one indicating that an interface roughening transition occurred and, as a result, the anisotropy in interfacial energy was considerably reduced. Grain growth behavior was also strongly dependent on the interface structures; while normal grain growth occurred when the interfaces were rough, abnormal grain growth behavior was observed in the samples with faceted interfaces. It appears, therefore, that the ionic vacancies in SrTiO 3 can cause the interface roughening transition and change the resultant grain growth behavior.