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>Neutron quasielastic scattering study of the ammonium ion reorientations in a single crystal of NH4Br at 373 deg;K
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Neutron quasielastic scattering study of the ammonium ion reorientations in a single crystal of NH4Br at 373 deg;K
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机译：Neutron quasielastic scattering study of the ammonium ion reorientations in a single crystal of NH4Br at 373 deg;K
The ammonium ion reorientations in a single crystal of NH4Br in its disordered CsCl phase have been investigated by quasielastic neutron scattering at 373deg;K. Neutron spectra were measured at four different crystal orientations (with the 110 planes of the crystal in the scattering plane) and data were recorded simultaneously at a variety of scattering angles providing a range of momentum transfers for elastic scattering, 0.5 Aring;minus;1le;Qle; 2.5 Aring;minus;1. The experimental results were fit to models allowing instantaneous random jumps around the C2and C3axes of the (NH4)plus;ions using a variety of analytical procedures that are described in some detail. The results of these fits establish conclusively that the ammonium ion reorientations are dominated by 90deg; jumps around the C2axes with an average time tgr; between jumps of 3.2plusmn;0.4 psec at 373deg;K. The inelastic part of the measured neutron spectra shows a torsional vibration peak at 305 cmminus;1, in good agreement with previous values. The results and analysis demonstrate the value of single crystal measurements in neutron studies of dynamic orientational disorder in solids.
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