Infrared reflectivity study of the phase transitions in sodium ammonium sulfate dihydrate

Re-refinement of sodium ammonium sulfate dihydrate at 170 K

The crystal structure of sodium ammonium sulfate dihydrate has been redetermined at 170 K on the basis of single-crystal X-ray data.

The title compound, sodium ammonium sulfate dihydrate (SASD), NaNH₄SO₄·2H₂O, a synthetic analogue of the mineral lecontite, is a well known ferroelectric. The crystal structure of the paraelectric phase has been re-refined at 170 K on the basis of single-crystal X-ray data, improving the previous study [Arzt & Glazer (1994 ▸). Acta Cryst. B50, 425–431] in terms of accuracy regarding hydrogen-atom positions and thus details of the hydrogen bonding. O—H⋯O and N—H⋯O hydrogen bonds between the principal building units [Na(OH₂)₄O₂ octa­hedra, SO₄ tetra­hedra and ammonium cations] constitute a three-dimensional network structure.