Lattice location of rare-earth ions in LiNbO3

The lattice location of three rare-earth ions (Pr3+, Ho3+, Yb3+) in LiNbO3 is investigated using Rutherford backscattering spectrometry/channeling techniques. All of them are found to occupy the Li+ octahedron but shifted from the Li+ regular position by different amounts (−0.45 Å for Pr3+, −0.38 Å for Ho3+, and −0.3 Å for Yb3+) as previously reported for other rare-earth ions. The amount of displacement is directly related to the variation of the ionic radius of the rare-earth ion, oppositely to transition metal ions which are not shifted. A simple model based on electronic configuration is given to account for this behavior.