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.