Raman spectra of crystals in the proton glass state

Abstract

Polarized Raman spectra of Cs 5 H 3 (SO 4 ) 4 • H 2 O (PCHS) single crystals were measured in the frequency range 0-4000 cm −1 at 20-300 K, i.e. both below and above the glass transition temperature (T g ). The evolution of the spectra with decreasing temperature indicates that the orientational disorder of SO 2− 4 ions and H 2 O molecules changes at T g from the dynamical to a static one. A scenario for the glass transition and a model of the resulting glass state is suggested, in which the water molecules (H bonds) play the role of binding constituents of the isolated sulphate complexes H 3 (SO 4 ) 5− 4 .

Fast proton conducting hydrogen sulphates and selenates: Impedance spectroscopy, Raman scattering and optical microscope study

“…In M 3 H(XO 4 ) 2 crystals an increasing rotational disorder of XO 4 groups, involved in O 3 XO -HIIIOXO 3 dimers, is observed on heating already below T S [15]. As a result disorder of protons in Hbonds also increases and finally a state of completely disordered H-bond network is reached at T S .…”

H-bond network dynamics of the solid-state protonic conductor Rb3H(SeO4)2 from FTIR and IINS measurements

“…Infrared spectra of Rb 3 H(SeO 4 ) 2 between 800 cm À1 and 1100 cm À1 at 298 K (monoclinic phase); measurements of a small crystal (30Â30Â3 Am) using the Bruker IFS66/MCT-D26 FTIR-microscope spectrometer; fit of the measured spectra with nine Gaussian functions, as well as with three background functions (dashed). The nine bands observed in the IR spectra, characteristic of internal vibrational modes in Rb 3 H(SeO 4 ) 2 , were assigned by comparison with literature data (Rb 3 H(SeO 4 ) 2 [6,17,[19][20][21], H 2 SeO 4 [22] and KHSeO 4 [23]), together with the results of the comparative factor group analysis and with the IINS results [14]. In the range of strong OH bondings (O. .…”

“…[4]). If we carry out the factor group computation for this disordered hydrogen atom, we find nine vibrational modes (A 1u +E u +2A 2u +2E u ) and not three modes, as it should be [6,16]. It is not possible to divide the result in a useful way or to find a non-disordered position for the hydrogen in the centrosymmetric trigonal structure, and therefore this atom cannot be included into this comparative factor group analysis.…”

“…In the literature already numerous results of factor group analysis on Rb 3 H(SeO 4 ) 2 have been published, however, with conclusions not always consistent with each other [6,16,17]. In order to present a comparative factor group analysis for both the monoclinic and the trigonal phase of Rb 3 H(SeO 4 ) 2 , it is necessary to present this analysis in some more detail.…”

“…Polarized Raman scattering studies have shown the off-center positions of protons in the O-H. . .O bonds, which is equivalent to a non-centrosymmetric H[SeO 4 ] 2 3À dimer [6]. Proton conductivity in Rb 3 H(SeO 4 ) 2 is related to a dynamic disorder in the form of an intracrystalline chemical equilibrium reaction [7,8].…”