Phase transitions and lattice dynamics of ammonium nitrate

New investigations of the phase transitions of ammonium nitrate (AN) used as oxidizer in solid propellants, explosives, and gas generator systems were carried out with temp. resolved x-ray diffraction (TRXRD) measurements using Rietveld anal. for evaluation. The transition paths of AN esp. during the cooling cycle after heating were complemented by quant. phase anal. providing information about the phase concns. in the temp. regime of phase coexistence. The curves for the elementary cell parameters of the different phases as a function of temp. exhibit hitherto unknown details and elucidate expansion and transition mechanisms. They are used for the calcn. of the vol. changes during the transitions and the volumetric and linear expansion coeffs.