Ab initio Atomistic Thermodynamics of the (001) surface of Strontium Titanate

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In this thesis I studied the atomic scale models that were proposed to understand the surface reconstructions observed on SrTiO3 (001). I investigated these atomic scale models using first principles calculations. Two newly proposed models for SrTiO3(001) were studied: the so called Sr adatom model and the double layer model. In particular, I have focused on the models proposed to explain the (2×1) and c(4×2) reconstructions on SrTiO3(001), and on the set of surface phase transitions observed by Kubo and Nozoye on SrTiO3(001).

To achieve this goal, I have used first principles atomic scale thermodynamics. This tech- nique links concepts and techniques from thermodynamics with results obtained from atomistic electronic structure theory. Since most of the experimental evidence comes from Scanning Tunnelling Microscopy (STM), I have complemented the analysis with simulations of the observed STM images for different surface reconstructions.

The results for the set of surface phase transitions observed by Kubo and Nozoye show that the lower Sr coverage implied in the Sr adatom model can only be explained if the surface is far from equilibrium, in a transient state as it loses Sr to the environment. Depending on the values of the environmental variables, stable atomic scale models were found for the (2×1) and c(4×2) reconstructions.