Ion implantation in TiO2:: Effect of the charge state on the lattice site occupation

Ions with different charge states Hg(+2), Sn(+4), Sb(+5), and Pb(+4) were implanted in TiO2 (rutile) and their lattice site location was determined using Rutherford Backscattering and Channeling (RBS-C). The maximum solubility concentrations on Ti sites (+4) were about 5 x 10(13) cm(-2) for Hg, 1 x 10(15) cm-2 for Sb and greater than 3 x 10(15) cm(-2) for Sn. For Pb a value of 5 x 10(13) cm(-2) was observed, although Pb should be insoluble as estimated from the solid solubility rules. The results cannot be explained by the size mismatch energy, as in the case of metals but seem to depend on the charge state. The non-substitutional fractions were larger for Hg and Sb, having a net charge on Ti sites. This behavior is attributed to the formation of impurity-defect complexes, where it is electrostatically favorable for different defects to associate for charge compensation. Supersaturation is reached for Pb, where charge compensation is not required. (C) 1998 Elsevier Science B.V.