Absolute atomic arrangement and spontaneous polarization in ferroelectric LiH₃(SeO₃)₂

The sense of the spontaneous polarization P_s for ferroelectric LiH₃(SeO₃)₂ has been related to the absolute atomic arrangement with the use of anomalous scattering of neutrons from ⁶Li. The polar axis is almost parallel to the crystallographic c* axis. The absolute sense of P_s is antiparallel to c* with an experimentally determined magnitude of 15 × 10^-2 C m-2. The calculated value, assuming point charges for Li⁺, H⁺, Se⁴⁺ and O^2- is -9.8 x 10^-2 C m^-2. LiH₃(SeO₃)₂ belongs to the three-dimensional class of ferroelectrics with essentially random displacement directions of the atoms at polarity reversal. The large value of P_s is the result of the oxygen displacements all having the same sense along the polar axis.