Ammonium nitrate phase stabilized with diammine copper dinitrate was cycled between -70 and 100 degreesC in steps of 10 degreesC, while diffraction patterns were measured after each step. The measured sries were used for phase identification and for Rietveld analysis, whichn delivered the elementary cell parameters and quantitative phase analysis for temperature regions with coexisting phases. Expansion coefficients were calculated using the elementary cell data. During cycling the phases II and IV were observed exclusively. Phase IV changes on heating into phase II, which on cooling reconverts into IV. With a CuO-concentration of 3 wt.% the transitions are complete, whereas with 5 and 7% CuO only partial reconversion is observed into phase IV at essentially lowered transition temperatures with parts of the sample existing until -70 degreesC in phase If or the similar phase V, which are not easily distinguishable.