Atom by atom analysis of defect structures in doped STO

SrTiO3 (STO) is one of many complex oxide materials, which are of high interest in a
plethora of technological applications due to their wide range of magnetic and electronic
properties. Introducing small amounts of dopants and/or vacancies into the materials can
tailor these properties over a wide range. Therefore, information about the electronic and the
structural configuration of defects is essential. In metal oxides such as STO, solids are
ionically bonded with many types of defects that shape the properties. 0D-defects or point
defects play a major role regarding controlling and optimizing these materials. Figure 1
shows different point defects in ionic compounds. The materials chosen for method
development and optimization is STO, doped with low concentrations of Ta or Al. By
leveraging the various modalities available in an aberration corrected STEM, such as
integrated differential phase contrast (iDPC) imaging, annular dark field (ADF) imaging and
core-loss electron energy loss spectroscopy (EELS), we deduce information about the
distribution and defect structure of the point defects introduced by doping on an atomic level.
This requires extremely thin samples (< 20 unit cells), prepared through wedge polishing.
Precise thickness determination of crystalline parts will be performed by position averaged
convergent beam electron diffraction (PACBED) measurements, in order to allow direct
quantitative comparison with MS
simulations based on atomistic
modelling. Our main focus lies on
the presence of O and Sr
vacancies. Preliminary results
obtained from STO:Ta are
illustrated in Figure 2. The highangle
annular dark-field (HAADF)
signal demonstrates a 30%
intensity increase at certain TiO
atom columns, indicating the
presence of Ta atoms within
those positions. Additionally, a
minor decrease in Sr intensities
adjacent to identified dopant
sites is observed, suggesting the
possible existence of Sr
vacancies near Ta dopants.