Neutron-diffraction measurements on theP-Tphase diagram of ammonium bromide

The $P$-$T$ phase diagram of N${\mathrm{D}}_4$Br and N${\mathrm{H}}_4$Br has been investigated by neutron-diffraction techniques. Although many of the features previously reported have been confirmed, a new high-pressure phase could not be found. Measurements of the hysteresis of the II-III transition as a function of pressure indicate that the transition is discontinuous at all pressures and that no tricritical point exists along this phase line. The lattice constant of N${\mathrm{D}}_4$Br has been measured as a function of temperature by x-ray diffraction.