Crystal Structure of Ferroelectric Li${\mathrm{H}}_3$${\left(\mathrm{S}\mathrm{e}{\mathrm{O}}_3\right)}_2$

The structure of the room-temperature ferroelectric Li${\mathrm{H}}_3$ ${\left(\mathrm{S}\mathrm{e}{\mathrm{O}}_3\right)}_2$ has been determined by x rays, using the heavy-atom method, and refined on the IBM 704. The crystals are monoclinic, with space group $\mathrm{Pn}$ and $a={6.25}_8$ A, $b={7.88}_6$ A, $c={5.43}_3$ A, $\beta =105.2\mathrm{}°$. Fairly strong O—H...O bonds with distances 2.52, 2.56, and 2.57 A are found, nearly perpendicular to the polar direction. The O—Se—O angles in one of the two selenite ions are rather similar; in the other ion these angles are unequal, as in the structure of ${\mathrm{H}}_2$Se${\mathrm{O}}_3$. Possible positions for the Li ions are given based on crystal-chemical considerations.