Coupled Modes With A1 Symmetry In Tetragonal Batio3

The infrared properties of a system of first-order-coupled phonons are analyzed. The dielectric function and the Raman line shape of the polariton modes are derived. The parameters involved in the theory can be obtained from the Raman spectra of the TO and LO modes or from the Raman spectrum of the TO modes plus infrared-reflectivity measurements. It is shown that we can objectively distinguish real coupling from imaginary, contrary to the current belief. Numerical calculations are performed for the A1-symmetry modes of tetragonal BaTiO3, with good agreement for the polariton shapes and complete disagreement for the infrared reflectivity; damage at the crystal surface is pointed out as the probable cause of the discrepancy. In addition to the coupling between the lowest and the middle mode, previously known, a much larger coupling between the middle mode and the highest is shown to exist. Both couplings are shown to be real or nearly so. The discrepancy between the dielectric constant created by the resonant modes (electronic plus phonons) and the value obtained by electrical measurements is interpreted as a new indication that the crystal has a dynamical disorder; this disorder could also be cause of an anomalous broadening observed in the lowest polariton. © 1974 The American Physical Society.10835223533Information, Control and Communication (INSTICC),Institute for Systems and Technologies o

Temperature Dependence Of Dipolar Modes In Ferroelectric Batio3 By Infrared Studies

Temperature dependence of A1 modes in tetragonal phase and F1u modes in cubic phase of BaTiO3 has been studied by ir (infrared) reflectivity measurements. The spectra have been analyzed using Kramers-Kronig analysis and the coupled-mode classical oscillator fit. The results are in excellent agreement with each other and are compatible with the earlier Raman measurements. Such a compatibility indeed favors the conclusion of Pinczuk et al. with regard to the interpretation of the broad peaks at 270 and 520 cm-1 in the Raman spectrum to be of first order. A critical analysis of the earlier work in BaTiO3 is presented. © 1980 The American Physical Society.2252396240

Raman Scattering In Hydrogen Halide Gases

We have measured the Q branch vibrational Raman cross sections of the hydrogen halide gases HCl, HBr, and HI relative to that of N2. We also measured the variation of the HI cross section as a function of the incident laser frequency. The absence of preresonance behavior in HI suggests that the virtual states primarily responsible for Raman scattering lie near or above the ionization potential. This in turn implies that the variation of the Raman cross section among the hydrogen halide molecules results primarily from a variation in the magnitude of the dipole matrix elements rather than from a variation in the energy of the virtual states involved. Copyright © 1975 American Institute of Physics.6393996400

Mixing Of Internal Modes Of Different Molecular Symmetry In Liio3

We present experimental data which show that there is a smooth and continuous frequency and polarization variation with phonon propagating directions in single-crystal LiIO3, which implies a mixing of phonon symmetries at k=0 and continuous mixing of internal vibrational modes of the IO3-ion. © 1970 The American Physical Society.162818282

Phonons, Polaritons, And Oblique Phonons In Liio3 By Raman Scattering And Infrared Reflection

A detailed Raman-scattering investigation of LiIO3, combined with the polarized infrared-reflectivity measurements, is reported. The dielectric constants determined by the Lyddane-Sachs-Teller (LST) relation (εxx=6.7,εzz=6.1) do not reveal any large contribution by the lattice dynamics to the low-frequency dielectric response. The high-temperature study of the TO Raman modes (till 220°C) does not show any mode "softening, " which could explain the critical dielectric behavior observed at very low frequencies. The study of the A-symmetry polariton curves has reconfirmed the LST dielectric values. The angular dispersion of the two upper oblique phonons of the A and E1 symmetry is compared with theory. The intensity dependence of these oblique phonons enables the determination of the second-harmonic- generation coefficient d13 and the linear electro-optic coefficient r13 in LiIO3. These values are compared with other published data. © 1971 The American Physical Society.4124542455

Debye-like Diffusive Central Mode Near The Phase Transition In Ferroelectric Lithium Tantalate

We report a clear cut evidence of a temperature dependent diffusive central mode associated with the ferroelectric phase transition of LiTaO3; a detailed linshape analysis shows that this central mode is a Debye-like relaxation. We also show its influence in the dielectric constant through polariton measurements for several temperatures. © 1976.196491494Devonshire, Theory of ferroelectrics (1954) Advances in Physics, 5, p. 85Cochran, Crystal stability and the theory of ferroelectricity (1960) Advances in Physics, 9, p. 387Anderson, (1960) Fizika Dielekrikov, p. 290. , G.I. Skanavi, Acad. Nauk. USSR, MoscowFirstein, (1974) PhD Dissertation, , University of Southern California, Los AngelesDidomenico, Jr., Porto, Wemple, Evidence from Raman Scattering for an Overdamped Soft Optic Mode in BaTiO_{3} (1957) Physical Review Letters, 19, p. 855Johnston, Jr., Kaminov, (1968) Phys. Rev., 168, p. 1045Penna, (1974) PhD. Dissertation, , University of Southern California, Los AngelesScalabrin, (1974) PhD. Dissertation, , University of Southern California, Los AngelesFritz, Reese, Brody, Wilson, Cummins, (1971) Light Scattering in Solids, p. 415. , M. Balkanski, Flammarion, ParisSteigmeier, Harbeke, Wehner, (1971) Light Scattering in Solids, p. 396. , M. Balkanski, Flammarion, ParisNassau, Levinstein, Loiacono, Abrahams, Reddy, Bernstein, Hamilton, (1966) J. Phys. Chem. Solids, 27, p. 983Glass, (1968) Phys. Rev., 172, p. 564To be reported and discussed in detail elsewhereAndrade, Prasad Rao, Katuar, Porto, Analysis of the relationship between temperature dependence of the libration mode and dielectric relaxation in NaNO2 (1973) Solid State Communications, 12, p. 847Coombs, Cowley, (1973) J. Phys., 6 C, p. 121Mason, Theory of the Ferroelectric Effect and Clamped Dielectric Constant of Rochelle Salt (1974) Physical Review, 72, p. 854Andrade, Porto, (1974) Ann. Rev. Mat. Sci.Riste, Samuelsen, Otnes, (1971) Solid State Commun., 9, p. 1455Shirane, Axe, (1971) Phys. Rev. Lett., 27, p. 1803Scott, Soft-mode spectroscopy: Experimental studies of structural phase transitions (1974) Reviews of Modern Physics, 47, p. 83Huang, On the Interaction between the Radiation Field and Ionic Crystals (1951) Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences, 208, p. 35

Light Scattering By Lithium Tantalate At Room Temperature

The room-temperature Raman spectra of LiTaO3 for all symmetry phonons are investigated. We make a new assignment of the phonons, which agrees with the selection rules of a C3 symmetry instead of C3v, contrary to Kaminow and Johnston's previous work. The oblique phonon dispersions are obtained and turn out to be consistent with our phonon assignments. We obtain also the polariton dispersion curve and, from it, the low-frequency dielectric constant. © 1976 The American Physical Society.13114907491

Temperature Dependence Of The Broad A1 (to) Phonon Raman Linewidth In Batio3

The temperature dependence of the A1 (TO) broad phonon linewidth is discussed. It is shown that it can adequately be accounted for by assuming a simple model where the Ti ions are sitting off the center of the unit cell and tunneling through a double well in the direction of the ferroelectric axis. © 1977.244291294Scalabrin, Porto, Chaves, (1975) Third International Conference on Light Scattering in Solids, p. 861. , M. Balkansky, R.C.C. Leite, S.P.S. Porto, Flammarion Sciences, ParisScalabrin, Chaves, Shim, Porto, (1977) Phys. Stat. Sol. (b), 79, p. 731. , see alsoMason, Matthias, (1948) Phys. Rev., 74, p. 1622Park, (1967) Phys. Lett., 25 A, p. 490Pine, Tannenwald, (1969) Phys. Rev., 178, p. 1424Andrade, Prasad Rao, Katiyar, Porto, Analysis of the relationship between temperature dependence of the libration mode and dielectric relaxation in NaNO2 (1973) Solid State Communications, 12, p. 847Andrade, Porto, On linewidth of phonons associated to a disorder mechanism (1973) Solid State Communications, 13, p. 1249Prasad Rao, Andrade, Porto, Temperature Dependence of the Libration Mode and Dielectric Relaxation of NaNO3 (1974) physica status solidi (b), 61, p. K71Maradudin, Fein, (1962) Phys. Rev., 128, p. 2589Kemble, (1958) The Fundamental Principle of Quantum Mechanics, , Dover Publications Inc, New YorkKemble, (1935) Phys. Rev., 48, p. 549Wemple, Di Domenico, Jr., Camlibel, (1968) J. Phys. Chem. Solids, 29, p. 179