Density-functional calculations were carried out for the (113)[¯110] tilt grain boundary in anatase, with and without magnetic Co dopants. The boundary exhibited a low energy (0.88J/m2), with no rigid translation of the grains. It was composed of 4 distinct structural units, and a deviation from the mirror-symmetrical atom arrangement was found, due to local relaxation. Analysis of the electronic structure indicated that the grain boundary was electronically inactive, because it introduced no boundary-specific states into the bulk band-gap. Only minor differences between the valence-band structures of the grain boundary and the pure bulk were obtained. The regular arrangement of the relatively open structural units provided the possibility of doping the grain boundary with electronically or magnetically active elements. This was explored by doping the super-cell with Co. In this dilute magnetic semiconductor, the (113)[¯110] grain boundary could enhance the ferromagnetic interaction by providing convenient bond angles for ferromagnetic super-exchange.

Density-Functional Investigation of the (113)[−110] Twin Grain Boundary in Co-Doped Anatase TiO2 and its Influence on Magnetism in Dilute Magnetic Semiconductors. S.Gemming, R.Janisch, M.Schreiber, N.A.Spaldin: Physical Review B, 2007, 76[4], 045204 (10pp)