No abstract

The crystal structure has been determined for NH 4 H 2 P0 4 and ND 4 D 2 P0 4 at atmospheric pressure, and for NH 4 H 2 P0 4 at a hydrostatic pressure of 8.9 kbar. In each case the temperature was set to just above the antiferroelectric-to-paraelectric phase transition. The relationship between the transition temperature and the Ο -Η-O and O -D -O bond dimensions is discussed in comparison to the isomorphous but ferroelectrically ordering KH 2 P0 4 and KD 2 P0 4 .