Study on atomic coordination around Er doped into anatase- and rutile-TiO2:: Er-O clustering dependent on the host crystal phase

Alternative Er doping into anatase (A-) or rutile (R-) TiO2 can be achieved by O-2 pressure control during Er-doped TiO2 deposition using laser ablation. An x-ray absorption fine structure analysis of the atomic coordination around Er revealed the dynamics of Er-O clustering in A- and R-TiO2. The Er local structure in A-TiO2 can be determined by a Ti-O arrangement of the host crystal surrounding Er, while that in R-TiO2 can be decided by the Er-O chemical properties rather than the Ti-O arrangement. Moreover, a substitution of Er for Ti induced 0 deficit in A-TiO2 and induced Ti removal in R-TiO2. These differences can be explained by the ErO6 stabilization mechanism based on the spontaneous symmetry reduction (SSR) theory. The Ti-O arrangement in A-TiO2 prevents the SSR, resulting in ErO6 instability. However, ErO6 is stabilized in the host crystal because the SSR is smoothly induced in R-TiO2. (C) 2003 American Institute of Physics.