Structure and properties of amorphous SrTiO₃: a first principles study

Recent discoveries of amorphous and quasi-amorphous phases in SrTiO₃ (a-STO) open up a wide range of possible applications in electronic devices that prohibit utilization of crystalline STO (c-STO) due to fundamental or technological barriers. While oxygen vacancies are known to play key role in the electronic properties of c-STO, the results may not be applicable to a-STO. Upon amorphization, changes in the local structure and morphology may affect the formation energy of oxygen defects and their diffusion. In addition, a reduction of the material’s density may lead to voids and other structural defects, important for material’s behavior. All the above calls for a comprehensive study of the microscopic origins of the observed electronic and optical properties in a-STO.
Here we employ ab-initio molecular dynamics liquid-quench simulations and accurate density-functional calculations to understand how the local and medium-range structural characteristics change upon amorphization in STO. Specifically, we analyze the Ti-O and Sr-O coordination, polyhedra sharing, and morphology as a function of density, quench rates, and oxygen deficiency in a-STO and determine the role of the structural changes in the resulting electronic and optical properties of this disordered material.