Phase relations of NH 4ClO 4 and NH 4BF 4 to high pressures

The high pressure phase diagrams of NH ₄ClO ₄ and NH ₄BF ₄ were studied by means of differential thermal analysis and volumetric techniques. The high temperature portions of these diagrams are intermediate between those of the corresponding potassium and rubidium salts, but at low temperatures the onset of hydrogen bonding causes the appearance of phases which are unique to the ammonium compounds.