Spectroscopy of phase transitions
The study of phase transitions in organic and inorganic crystals was one of the main subjects of research
work in the Laboratory for many years. New, previously unknown, phase transitions were found [1-6] being
confirmed later by X-rays and calorimetric studies. It was proposed for the first time to use the temperature
dependence of the intensity of phonon lines (FIR and RS [2-4]), or Davydov and/or Bethe splitting of intermolecular
vibrations [5] as the order parameter in the vicinity of phase transition. The ferroelectric phase stabilization near the
surface of TlGaSe2 crystal was observed [6]. The effect of the proton dynamics on Raman spectra and the
manifestation of the protons and deuterons tunneling in Raman spectra of the nonlinear crystals Rb(DxH1-x)2PO4 [7].
The separate series of works are forming the RS studies of phonon spectra and their transformations with
the change of hydrostatic pressure up to 12 Kbar in semiconducting crystals of the types A IIIBV and AIIIBIIIC2VI.
Nearly 50 compositions were studied, new phase transitions have been discovered in some of them.
After
discovery
of
high-temperature
superconductivity (HTSC) the spectroscopy of HTSC and
related materials has been as a new trend in the Laboratory.
We stated a problem correctly to obtain and intepret the
Raman spectra (Fig. 1), to study both the interaction of the
electron continuum with the phonon subsystem and the
correlation between the spectra and the superconducting
properties of HTSC [8,9].
Fig. 1. The frequency dependence of Ag-modes on the oxygen
content in YBa2Cu3Ox [9].
We have studied the temperature dependences of the
Raman spectra of the lithium-containing superionic crystals.
It is found, that the widths and the frequencies undergo
anomalies at the superionic transition in the LiNbGeO5
crystal. It is revealed that an interference of one-phonon
optical low-frequency modes (an antiresonance) appears with the temperature increase of the -Li3PO4 crystal. The
numerical analysis of the spectrum in the interaction region has shown the strong temperature dependence of the
coupling constant defined by the anharmonic coupling of optical and acoustical modes [10].
1.
G.N.Zhizhin. Spectroscopy of low temperature crystal phases of organic substances. Crystalography,
v.18(4), 769 (1973).
2. N.I.Afanasyeva, V.M.Burlakov, G.N.Zhizhin. Phonon spectrum in the vicinity of phase transition «crystalnematic» and the ordering parameter. JETP, v. 23(9), 508 (1976).
3. G.N.Zhizhin, YU.N.Krasyukov, Ye.l,Mukhtarov, V.N.Rogovoy. Anisotropy of rotational reorientations of
cyclohexane near the phase transition point. Letters to J ETP, v.28, 465 (1978).
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the phase transition. Soviet Physics, Solid State, v.18, 2826 (1976).
5. G.N.Zhizhin, E.I.Mukhtarov,Optical spectra and lattice dynamics of molecular crystals ( in Vibrational
spectra and structure, ed. J.R.Durig) v.21, 447, Elsevier, Amsterdam, 1995.
6. N.I.Agladze, B.P.Antonuk, V.M.Burlakov, E.A.Vinogradov,G.N.Zhizhin. Structural phase transition in
near-surface layer. Fizika Tverdogo Tela, 23, 3289 (1981).
7. B.N.Mavrin, Kh.E.Sterin, L.N.Rashkovich, A.V.Misthenko. Low-frequency spectrum and tunneling
protons (deuterons) in the Rb(DxH1-x)PO4 crystals. Fizika Tverdogo Tela, 15, 3702 (1973).
8. V.N.Denisov, A.F.Goncharov, B.N.Mavrin,V.B.Podobedov. Raman scattering in high-Tc superconductors
Yba2Cu3Ox with different oxygen contents. In: Laser Optics of Condensed Matter. (Ed. E.Garmire,
A.Maradudin, K.Rebane), Plenum Press, New York, 1991.v.2, p. 131.
9. V.N.Denisov, B.N.Mavrin, V.B.Podobedov. Raman spectroscopy of the high temperature superconducting
YBa2CuOx single crystals and films. Phys.Rep., 194, 397 (1990).
10. B.N.Mavrin, V.V.Asonov, V.V.Fomichev, A.K.Ivanov-Shits, V.V.Kireev. Raman scattering, interaction
and interference of optical vibrations in the -Li3PO4 superionic crystal. JETP, 96, 53 (2003).