Raman spectra of a LiN(H_xD_1‐x)₄SO₄ mixed crystal

Abstract

Raman spectra of a deuterated lithium ammonium sulphate single crystal are studied a t 77 to 493 K. The results show that the 1-11-111 phase transitions are bonded essentially with the dynamics of Li-SO, framework; the NH,-spectra are of a diffusive character so that no clear-cut conclusions can be drawn about the role of the NH,-sublattice in these phase transitions. The spectra corroborate the necessity of using several order parameters in the phenomenological description of the phase transitions in this crystal. M3Y'IaH)TCFI CneKTpbI fcp AefiTepMpOBaHHOrO MOHOKpMCTaJIna JIMTMfi-aMMOHHfi CyJIbqaTaIIpM 77 A 0 493 K. Pe3ynbTaTbI nOKa3bIBaH)T, 9 T O @a30BbIe IIepeXOAbI 1-11-111 CyUeCT-BeHHO CBR3aHbI C AMHaMMHOfi KapKiCa Li-so, ; CIIeKTpbI NH,, MMeH)T AH#@Y3MOHHbIfi XapaKTep, 9 T O He II03BOJIFIeT OnpeAeJIllTb OAH03Ha9HO p0nb IIOApeILIeTXM NH, B 3TMX IIepeXOHaX. CIIeKTpbI n0~TBepmAaloT HeO6XOAMMOCTb MCIIOJIb30BaHMR HeCKOJIbKPiX IIapaMeTpOB nOpHAKa IIpll @eHOMeHOnOIX9eCKOM OIIMCaHMM @a3OBbIX IIepeXOAOB B 3TOM Kpmxanne.

Coexistence of the soft mode and sub-THz central peak in ferroelectric BaTiO3/(Ba,Sr)TiO3 superlattices

“…In addition to the soft mode, the relaxator Debye-like central mode was observed at sub-Terahertz frequencies in BaTiO 3 single crystals [8][9][10][11], and in Ba 1-x Sr x TiO 3 ceramics and in polycrystalline films [12,13]. Similar low-frequency relaxations were also observed in other ferroelectric single crystals [15][16][17][18], and classical ferroelectric relaxor PbMg 1/3 Nb 2/3 O 3 due to polarization fluctuations [19]. Note however that the appearance of the central peak is not a general rule.…”

Raman scattering in lithium ammonium sulphate

“…Also given in Tables 2 and 3 for comparison purposes are the frequencies and assignments previously reported for deuterated LAS. 3 The assignments in these tables labelled vi, T and L are for internal vibrations, translations and librations, respectively. The superscripts S, H and D refer to SO4, NH, and ND, ions, respectively.…”

“…3. In the external modes region of the spectra few lines were observed: one B,, four B, and three A , symmetry modes, totalling eight instead of the 43 lines predicted.…”

Raman Spectra of [N(CH3)4]2ZnCl4 Single Crystals I. Raman Spectra of the Parent Phase

“…It should be noted that based on this assumption, an adequate identification was performed of the spectra of some crystals of the family in question [29,30, 331, so we shall stick to this hypothesis. In the latent phase of D& symmetry, BX, ions occupy the (c)-position of D,, symmetry.…”