Neutron Scattering Studies of Vibrational Spectra and Structural Transformations in Superionic Conductors CsHSO/sub 4/ and CsHSeO/sub 4/

摘要

The results of neutron diffraction (ND) and inelastic neutron scattering (INS) studies on phase transitions and vibrational spectra in powder samples of superionic conductors CsHSO/sub 4/ (CHS) and CsHSO/sub 4/ (CHSe) at pulsed reactor IBR-2 are reported. Three different phases (III,II,I) in CHS and only two phases (II,I) in partly deuterated crystal CsDsub(0.7)Hsub(0.3)SO/sub 4/(CDS) are observed in the temperature range 123-420 K. The structural transformation of the ferroelastic type from monoclinic phase II to a possibly tetragonal phase I in CHS (CDS) at the superionic phase transition temperature Tsub(c) = 414 K (412 K for CDS) is rather sharp as compared to those in CHSe where the structural transformation starts far below Tsub(c) = 400 K. Considerable changes in INS spectra at the superionic phase are observed in all crystals: a librational mode of SO/sub 4/ ( or SeO/sub 4/) groups in CHS (CHSe) becomes rather broad and gamma (OH)-proton bending mode softens and broadens. To explain the experimental results, a theoretcal model for ferroelastic transformation at Tsub(c) induced by the Slater order-disorder type superionic phase transition of protons on hydrogen bonds is proposed. 24 refs.; 12 figs. (Atomindex citation 18:006748)