Formation of Ruddlesden–Popper faults and polytype phases in SrO-doped SrTiO3

The formation of so-called Ruddlesden–Popper planar faults was studied in SrO-doped SrTiO3 for different quantities of SrO additions and sintering conditions. For small SrO additions we observed a microstructure with a uniform grain size distribution and the enrichment of SrO at the grain boundaries. Larger additions of SrO produced a microstructure of elongated grains containing random planar faults, polytypic lamellae of more or less ordered faults, and polytype loops within SrTiO3 grains. We showed that these SrTiO3 grains were elongated as a result of preferential growth of the polytypic lamellae. In addition, we discuss a correlation between the formation of planar faults embedded in the perovskite matrix at low firing temperatures and Ruddlesden–Popper phases that are stable at higher temperatures.