Growth and defect crystal structure of CdF2 and nonstoichiometric Cd1−x R x F2+x phases (R = rare earth elements and In). Part 3. Crystal structure of As-grown Cd0.90 R 0.10F2.10(R = Sm-Lu, Y) single crystals

Abstract

The structures of as-grown Cd0.90R0.10F2.10 (R = Sm-Lu and Y) crystals are determined and related to the CaF2 structure type. It is assumed that in all the crystals R3+ and Cd2+ ions form clusters with the tetrahedral configuration of the [Cd2R2F26] and [CdR3F26] cations. The concentration of [Cd2R2F26] cations in crystals with R = Er-Lu and Y is considerably higher that in crystals with R = Sm-Ho. The tendency to a decrease in the coordination number of R3+ toward the end of the rare earth series manifests itself in the fact that the Yb3+ ions in Cd0.90Yb0.10F2.10 occupy both tetrahedral (c.n. 10) and octahedral (c.n. 8) clusters. The Yb3+ ions in tetrahedral clusters are displaced from their basic positions by 0.15 A along the 〈100〉 directions. In Cd1−xR x F2+x the relaxation of the anion sublattice of the fluorite matrix around clusters is much more pronounced than in the Ca1−xR x F2+x phases having similar geometry.