Inherent defects in sol-precipitation/hydrothermally derived SrTiO3 nanopowders

We have investigated sol-precipitation, coupled with a hydrothermal treatment, as a common solution-based method for the preparation of SrTiO3 nanostructured powders. XRD, FTIR, TG/EGA, Raman and TEM were employed for a detailed structural characterization of the sol-precipitates in comparison with subsequently hydrothermally or thermally post-annealed samples. The sol-precipitates exhibited a pseudo-cubic symmetry and adopted the morphology of the hydrolyzed Ti-precursor. The structural distortions were attributed to un-removed OH− groups and A-site vacancies, arising in the crystal lattice, as a result of a low-temperature diffusion-controlled reaction. Furthermore, we demonstrated that the microstructural characteristics of sol-precipitates are directly responsible for the formation of extended defects, i.e., nanocavities, within the single-crystalline particles, appearing independently of the selected post-annealing treatment, i.e., hydrothermal or thermal. The study revealed that local distortions and peculiarities on the microscale, introduced by sol-precipitation, were not completely restored under vigorous hydrothermal conditions, but rather provoked the formation of new microstructural defects with an additional treatment.