Lithium and sodium yttrium orthosilicate oxyapatite, LiY9(SiO4)6O2 and NaY9(SiO4)6O2, at both 100 K and near room temperature.

Lithium yttrium orthosilicate oxyapatite [lithium nonayttrium hexakis(silicate) dioxide], LiY(9)(SiO(4))(6)O(2), crystallizes in the centrosymmetric space group P6(3)/m at both 295 and 100 K. The structure closely resembles those of fluorine apatite and sodium yttrium orthosilicate oxyapatite [sodium nonayttrium hexakis(silicate) dioxide], NaY(9)(SiO(4))(6)O(2), which was also investigated, at 270 and 100 K, in this study. There are two different crystallographic sites for the Y(3+) ion, which are coordinated by seven and nine O atoms. One-fourth of the nine-coordinated site is occupied by Li or Na atoms, thus maintaining charge balance. The Si atom occupies a tetrahedral site. The two compounds show no symmetry change between room temperature and 100 K, and the alterations in structural parameters are small.