On the Metastable Transition and the Crystal Structure of Ammonium Nitrate (Tetragonal Modification)

Conditions for the appearance of the metastable transition (IV)\(\leftrightharpoons\)(II) were studied by X-ray method and dilatometer method and it was found that when the single crystals of the phase (IV) were formed from the aqueous solution at room temperature the metastable transition was always observed and that in dry ones it often proceeded as a single crystal transformation without any noticeable change in orientation. The crystal structure of the phase (II) was determined by using a single crystal obtained by the single crystal transformation. It was found that tetragonal modification (II) has also CsCl-like structure, and a hindered rotation of the nitrate groups was proposed.