Several perovskite ceramics are known to show non-Arrhenius grain growth. In particular for strontium titanate a grain growth transition was documented with decreasing grain growth rates with increasing temperature. Other materials as barium titanate, lithium lanthanum titanate and barium strontium titanate indicate grain growth transitions as well. The growth transitions are coupled to bimodal microstructures and seem to be caused by the existence, coexistence and transition of different grain boundary types.
The present study investigates the impact of acceptor dopants on bimodal grain growth in strontium titanate. With increasing acceptor dopant concentration an increasing population of small grains arises. At a concentration of 5 mol% Fe, hardly any grain growth is evident, and the grain size stays close to the powder particle size (~300nm). It was shown before via TEM and EDS that Fe segregates to the interfaces due to its negative charge and a positive boundary potential. Thus, the experimental findings seem to be well explained by the theory of solute drag: the diffusion of segregated defects (‘solutes’) at interfaces can retard grain boundary migration. This retardation depends on the defect concentration and on the local driving force. The implications for the grain growth transition of strontium titanate are discussed.