Copper phase-stabilised ammonium nitrate (Cu-PSAN) was prepared by the incorporation of copper(II) oxide (CuO) into the ammonium nitrate (AN) crystal lattice by a melt process. We studied the phase transitions of ammonium nitrate and dimensional changes occurring during this phase stabilisation process. Crystallographic aspects of the solid-state reaction between AN and CuO and thermal behaviour of phase-stabilised ammonium nitrate (PSAN) are discussed. It was found that solid-state reaction occurred by an intermediate solid solution formation. Lattice parameters and unit cell volume are calculated as a function of temperature from XRD patterns. They show a non-linear and anisotropic behaviour with increasing temperature. Lattice expansion along b-axis and contraction along a- and c-axes are observed. Unit cell volume increases with temperature. (C) 2006 Elsevier B.V. All rights reserved.