Transport phenomena in ammonium halides under high pressures

Polycrystalline ammonium chloride (NH4Cl), fluoride (NH4F) and bromide (NH4Br) were studied at pressures from 20 to 50 GPa in the temperature range of 77–400 K. Phase transitions from a highresistance to low-resistance state was found. The transition pressures were about 15 GPa for NH 4Br, 27 GPa for NH4Cl, and 42 GPa for NH4F. The transition temperatures and pressures were shown to depend on the preliminary pressure treatment. All ammonium halides show metal-like behaviour under high pressures, similar to that of alkali halides.