Structure and Stability of TiO2-B Surfaces: A Density Functional Study

We investigate the structure and energetics of low-index surfaces of
the TiO2-B polymorph by means of periodic density functional theory
calculations within the generalized gradient approximation. The bulk
structure contains two nonequivalent Ti ions, one of them exhibiting an
octahedral coordination, while the other is square-pyramidal. When
exposed at the surface, these two types of ions display different
relaxation schemes, which ultimately tend to make them more similar. On
the basis of the computed surface energies and of the Wulff
construction, we predict for TiO2-B a pseudohexagonal prismatic
equilibrium shape and an average surface energy practically identical
to that of TiO2-anatase.