The structure of ND4NO3 phase V by neutron powder diffraction

The crystal structure of ND4NO3 phase V was determined by the Rietveld refinement method for a series of neutron powder diffraction data measured at temperatures ranging from 10 to 250 K using a 90% deuterated sample. The unit cell was found to be orthorhombic, Pccn, with (at 78 K) a = 7.8850(2), b = 7.9202(2), c = 9.7953(2) A, and Z = 8. The final R indices were R(integ.) = 0.036, R(prof.) = 0.024 for the 78 K structure. The cations and anions are packed with a distorted CsCl-type arrangement and are linked together by two sets of three-dimensional hydrogen-bond chains. At ambient pressure, there are no other polymorphic phases (i.e. phase VII) down to 10 K. The thermal expansions of phases V, IV, III, and II were also measured accurately in this study (residual standard deviation less than 0.05 A3). (Auth.)