Nucleation and growth of planar faults in SrO-excess SrTiO3

A SrO-excess SrTiO3 polycrystalline ceramic was sintered at 1450°C for different times in order to study the anisotropic growth induced by the formation of SrO-rich planar faults inside the perovskite matrix. In the early stage of sintering the microstructure consisted of anisotropic perovskite grains containing polytypic lamella and a fine perovskite, which was free of planar faults. Further treatment caused a decrease in the anisotropy: elongated grains, due to the coarsening effect, developed into equiaxed perovskite grains containing polytypic lamellae. In order to study the preference for polytypic growth we used a SrTiO3 single crystal sintered in a SrO-rich atmosphere. We found that in the initial stage, fault-rich platelets were formed as discrete nuclei that had no crystallographic relation to the SrTiO3 single crystal. These platelets provided nucleation sites for a fault-free perovskite, forming sandwich-like composite grains. The single crystal acted as a source of SrTiO3 for the recrystallisation of these composite grains.