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  Dynamics of anions and cations in cesium hydrogensulfide (CsHS, CsDS): Neutron and x-ray diffraction, calorimetry and proton NMR investigations

Haarmann, F., Jacobs, H., Kockelmann, W., Senker, J., Müller, P., Kennedy, C. A., et al. (2002). Dynamics of anions and cations in cesium hydrogensulfide (CsHS, CsDS): Neutron and x-ray diffraction, calorimetry and proton NMR investigations. Journal of Chemical Physics, 117(10), 4961-4972. doi:10.1063/1.1479141.

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Haarmann, F.1, Author              
Jacobs, H., Author
Kockelmann, W., Author
Senker, J., Author
Müller, P., Author
Kennedy, C. A., Author
Marriott, R. A., Author
Qiu, L., Author
White, M. A., Author
Affiliations:
1Chemical Metal Science, Max Planck Institute for Chemical Physics of Solids, Max Planck Society, ou_1863405              

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 Abstract: Protonated and deuterated samples of the hydrogensulfide of cesium were studied by high-resolution neutron powder diffraction, calorimetry and proton NMR investigations in a wide temperature range. Primarily due to reorientational disorder of the anions, three modifications of the title compounds are known: an ordered low-temperature modification- LTM (tetragonal, I4/m, Z=8), a dynamically disordered middle- temperature modification-MTM (tetragonal, P4/mbm, Z=2), and a high-temperature modification-HTM (cubic, Pm (3) over barm, Z=1). The LTMreversible arrowMTM phase transition is continuous. Its order parameter, related to an order/disorder and to a displacive part of the phase transition, coupled bilinearly, follows a critical law. The critical temperature T- C=123.2+/-0.5 K determined by neutron diffraction of CsDS is in good agreement with T-C=121+/-2 K obtained by calorimetric investigations. For the protonated title compound a shift to T- C=129+/-2 K was observed by calorimetric measurements. The entropy change of this transition is (0.24+/-0.04) R and (0.27+/-0.04) R for CsHS and CsDS, respectively. The MTMreversible arrowHTM phase transition is clearly of first order. The transition temperatures of CsHS and CsDS are T=207.9+/-0.3 K and T=213.6+/-0.3 K with entropy changes of (0.86+/-0.01) R and (0.81+/-0.01) R, respectively. Second moments (M-2) of the proton NMR absorption signal of MTM and HTM are in reasonable agreement with M-2 calculated for the known crystal structures. A minimum in spin-lattice relaxation times (T-1) in the MTM could not be assigned by dipolar coupling to a two-site 180degrees reorientation of the anions, a model of motion presumed by the knowledge of the crystal structure. The activation enthalpies determined by fits of T-1 presuming a thermal activated process are in the order of molecular reorientations (E-a=13.5+/-0.5 kJ mol(-1) for the MTM and E-a=9.3+/-0.3 kJ mol(-1) for the HTM). In the HTM at T>330 K translational motion of the cations determines T-1 (E- a=13.8+/-0.4 kJ mol(-1)). (C) 2002 American Institute of Physics.

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Language(s): eng - English
 Dates: 2002-09-08
 Publication Status: Published in print
 Pages: -
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 Table of Contents: -
 Rev. Type: Peer
 Identifiers: eDoc: 17344
ISI: 000177574400043
DOI: 10.1063/1.1479141
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Title: Journal of Chemical Physics
  Alternative Title : J. Chem. Phys.
Source Genre: Journal
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Pages: - Volume / Issue: 117 (10) Sequence Number: - Start / End Page: 4961 - 4972 Identifier: ISSN: 0021-9606