The structure of ammonium hydrogen sulphate in its ferroelectric phase and the ferroelectric transition

Publisher Website
Google Scholar
Abstract
The structure of ammonium hydrogen sulphate (AHS) has been determined in an (010) projection from X-ray diffraction data collected photographically at - 81°C. At this temperature AHS is in its ferroelectric phase. The asymmetric unit of the pseudo-orthorhombic unit cell (space group Ba) contains four formula units which are related in pairs by a centre of inversion in the non-ferroelectric phase above - 3°C. It is shown that the ferroelectric structure corresponds to an ordering of sulphate groups which are disordered in the room-temperature structure, an ordering which is antisymmetric with respect to the room-temperature centre of inversion. This is the principal change: the relative movements of the other atoms are comparatively small.