This proposal seeks to identify and structurally characterise the high-pressure phases of the azide salts of sodium, silver, lead, and the ammonium ion. Azides are examples of energetic materials and play an important role in systems where the rapid release of energy and gas is required, e.g. detonators and air-bags. Study over a wide pressure range will allow accurate equations of state for the four systems to be established, thereby providing insight into the compressibilities of this class of compounds. Further phase transitions may be discovered and hence additional new forms could be identified. The results of these studies will extend our recently established programme to study energetic materials under high pressure, and will be of value to those to those seeking to predict and model the properties and performance of azides under extreme conditions.