Ammonium bromide is a fundamental ionic solid that finds practical use, industrially, as a highly-effective flame retardant and also as an intermediary source of bromide in pharmaceutical preparations. It is reported to possess six solid phases, under non-ambient pressures and temperatures, and these can be divided into three groups – those that show i) ferro-type (F) ordering of the NH4+ cation, ii) anti-ferro-type (AF) ordering or, iii) disorder, where the molecules tumble in a plastic phase. Almost no work has been carried out on exploring the wider phase diagram as a function of simultaneous non-ambient pressure and temperature. We aim to identify the location of pressure-temperature phase boundaries - literature studies predict an AF --> F --> AF ordering sequence at low temperature, with increasing pressure, and we will seek to determine if this re-emergent AF behaviour exists.