study of density-dependent structure of amorphous strontium titanate (a-SrTiO3)

Crystalline SrTiO₃ (c-STO), a common substrate material with singly terminated TiO₂ is crucial to grow complex oxide heterostructures. However, thin-films of c-STO suffer many limitations including high sensitivity to deposition process, heat treatment techniques and poor electrical properties compared to bulk STO. In contrast, amorphous materials of ABO₃ composition may provide an alternative route to attain structural stability and smooth surfaces while avoiding grain boundaries and internal lattice strain.

Understanding structure of amorphous strontium titanate (a-STO) presents a unique challenge since experimental results are contradictory with regards to tetrahedral vs. octahedral oxygen surrounding titanium (Ti). In this talk, we present a thorough ab initio-based study of a-STO explaining the existing discrepancy in the Ti coordination while validating both experiments. Our result reveals that the calculated pair distribution function, effective coordination number, and extended X-ray absorption fine structure vary significantly with density of a-STO. The reduced coordination of both Ti and Sr, disorder in polyhedral morphology, larger band gap and smooth vibrational density establishes striking differences between a-STO and perovskite structure in c-STO at 300 K.