Transverse Acoustic Waves Research Articles

INELASTIC NEUTRON SCATTERING STUDY ON ACOUSTICAL ACTIVITY OF Bi12GeO20 AND Bi12SiO20

Acoustical activity of isomorphous crystals Bi12GeO20 and Bi12SiO20 has been studied by measuring the splitting of degeneracy of transverse acoustical waves propagating along high symmetric direction with inelastic neutron scattering. One of the interesting results is that the left and right circularly polarized modes of acoustical phonons propagating along direction are subjected to different attenuation. This conclusion is verified by both kinds of crystals. The experimental result is observed for the first time in the study of acoustical activity. The life-time of the phonon with larger attenuation is found to be about 2×10-11 s. experimentally.

Brillouin scattering by transverse acoustic waves in NH4 LiSO4 near the ferroelectric transition

The elastic constant C55 and the combinations (C44 + C55)/2 and (C55 + C66)/2 have been investigated as function of temperature from Brillouin scattering spectra by transverse acoustic waves. The main feature is an increase for every constant below the transition. A broadening of the Brillouin peak corresponding to (C44+ C55)/2 is also observed. The results are discussed on the basis of a biquadratic coupling between the shear strains and the order parameter.

A study of acoustical activity of BiP 12GeO 20

Acoustical activity of Bi 12GeO 20 has been studied by measuring the splitting of the degeneracy of transverse acoustical waves propagating along the directions corresponding to acoustical axes, [100] and [111] with neutron inelastic scattering. A comparison with the experimental results of α-SiO 2 and NaClO 3 has been done. Three striking features of acoustical activity can be obtained from the present study. One of them is that the attenuation is different for right circularly polarized mode of acoustical phonon propagating along acoustical axes from left one. This effect might have applications in the future.

Acoustical Activity and Ferroic Crystals

Two theoretical formulations for explaining acoustical activity, namely the first-strain-gradient theory and the rotation-gradient theory, are described and compared. In the first-strain-gradient theory acoustical activity is determined by a fifth-rank tensor d, called the acoustic gyrotropic tensor. A new fourth-rank pseudotensor G has been defined by us which is completely equivalent to the tensor d. We also introduce the term “pure ferroacoustogyrotropy” to describe the effect in which the acoustic rotatory power of a crystal can be switched in sign (without change of magnitude) for transverse acoustic waves travelling along acoustic axes (axes of 3-fold or higher rotational symmetry). This effect can occur in ferroic crystals only. Twenty-nine Aizu species allowing it are identified. A number of crystals are predicted to exhibit this effect, the most convenient to study being lead germanate.

X-ray Study on the Intermediate Phase of Quartz

This article reviews our recent work on the α-β phase transition of quartz. The transition occurs on the four levels of spatial scale, namely through the structural change within the unit cell, the incommensurate modulation (150∼300 Å), the super modulation (30∼100 µm) and the formation of a domain structure (∼mm). The usefulness of X-ray topography or the combination with goniometry is emphasized. The incommensurate modulation waves are essentially a set of transversal acoustic waves which, however, is modified by a coupling with optical modes particularly near the α phase.

Picosecond impulsive stimulated brillouin scattering: Optical excitation of coherent transverse acoustic waves and application to time-domain investigations of structural phase transitions

A practical stimulated Brillouin-scattering method for spectroscopic characterization of low-frequency excitations is extended to permit optical generation and detection of phase-coherent transverse, longitudinal, and mixed polarization acoustic phonons, tunable over a wide frequency range, in solid media. Results are presented for BK-7 glass and the KH 2PO 4 crystal near its structural phase transition (SPT). Time-domain observations of acoustic phonon-induced ordering near SPTs in KH 2PO 4 and KD 2PO 4 were carried out, and applications of the technique to measurements of SPT dynamics are discussed.

Brillouin scattering study of the ferroelastic transition in some crystals with the scheelite structure

The structural phase transitions in BiVO4 and LaNbO4 have been studied by means of the Brillouin scattering. It has turned out that the velocity of a transverse acoustic wave propagating along a special direction [cosΘ0, sinΘ0, 0] decreases, showing a typical soft-mode behavior, as the transition temperature is approached both from above and below (the direction specified by Θ0 coincides with that of intersection of the tetragonal ab-plane and the ferro-elastic twin boundary observed in the monoclinc phase).

Propagation of Transverse Surface Acoustic Waves in Rotated Y-Cut Quartz Substrates Under Heavy Periodic Metal Electrodes

Abstmct-A theory of the propagation of transverse surface acoustic waves on a piezoelectric substrate with heavy periodic metal electrodes on the surface is presented. The mechanical properties of these electrodes are assumed to be nonnegligible. Dispersion relations for waves near the stopband of the periodic electrode array are analyzed. It is found that the mass of the electrodes exerts a considerable effect on the shape and mutual positions of the stopbands for short-circuited and electrically isolated electrodes. The discussion is based on an approximation for the effective surface impedance that relates the amplitudes of the electric and elastic fields observed at the surface of a piezoelectric substrate. The parameters of this approximation are given for rotated Y-cut quartz substrate. The theory presented can readily be generalized to the case of Rayleigh surface waves.

On the effect of the correlation in phonon motion on the viscosity of impure dielectrics

The effect of the correlation in phonon motion on the viscosity of impure dielectrics is studied. It is shown that for perfect dielectrics the relaxation times entering the expressions for the absorption of longitudinal and transverse acoustic waves are different due to phonon correlations. The influence of impurities on the viscosity of dielectrics is discussed. Special emphasis is given to the problem of longitudinal-acoustic-wave absorption in impure dielectrics. It is shown that the effect of impurities on phonon correlations can lead to a substantial change in absorption of longitudinal waves.

Rayleigh–Brillouin scattering of transverse and longitudinal acoustic waves in a supercooled viscoelastic liquid

Rayleigh–Brillouin spectra of 3-phenyl propanol are studied over the temperature range from −119.5° to 98.1 °C. The orientation relaxation time is obtained as a function of temperature. The depolarized spectra exhibit clear shear wave sidebands at temperatures below −29.5 °C. The polarized spectra give peaks due to the longitudinal acoustic wave whose frequency displays kinks at the glass transition temperature and at 37 °C (Tk). Tk is 55 °C above the melting temperature (−18 °C). The shear wave frequency decreases linearly with increasing temperature. The experimental results on the VH scattering spectra are analyzed according to viscoelastic theories based upon the Voigt and Maxwell models. Comparison of the theory with observed spectra shows that the Voigt model gives a better fit to the experimental data. Microscopic theory has also been developed to derive the Voigt and Maxwell models. Angular dependent studies are proposed to differentiate the various theories which give different predictions about the physical nature of the parameters.

Connection between the low temperature acoustic properties and the glass transition temperature of fluoride glasses

The variations of the velocity and the absorption of longitudinal and transverse acoustic waves have been measured in three fluoride glasses in the temperature range 0.1 K to 1.5 K. The density of states of two level systems (TLS) and the TLS - phonon coupling constants have been determined. The TLS density of states has been found to be inversely proportional to the glass transition temperature.

Magnetogasdynamic effects on the growth of transverse acoustic waves in a reacting gas

The growth of small disturbances is studied in an electrically conducting and reacting gas permeated by a magnetic field. The model extends to the magnetogasdynamic case some aspects of the theory of spinning detonation waves. It is shown that the stratification introduced by the applied magnetic field constrains the orientation of the propagation and that whilst the rate of wave growth is significantly impeded by the magnetic field it is not totally inhibited.

LIGHT SCATTERING FROM ACOUSTIC AND LOW-FREQUENCY VIBRATIONAL MODES IN BORATE GLASSES

Brillouin and low Raman scattering experiments have been performed on series of B203 xM20 glasses where = Li, Na, K, Rb, Cs, 11. The concentration and composition dependences of the velocity and attenuation of longitudinal and transversal acoustic waves have been measured, as well as those of the Raman peak. The composition and concentration dependence of the acoustic velocity seems to result from two competitive effects : the first one is related to the transition of boron atoms from three to four coordination with increasing x and the second one to the structural changes connected to the sterical hinderance of the M cations. The maximum of the boson peak has a behaviour similar to that of sound velocity. This similarity can be understood on the basis of the continuum theory of low-frequency Raman spectrum. Introduction. The binary borate glasses B203 x M20 are currently used as vitreous matrices for the elaboration of ionic conductors. In order to understand the conduction mechanisms in ternary systems (e.g. B203 xLi 20-y LiC£ or B203 x Li20yLi2S00 (7,2,3), it is necessary in a first step, to get structural informations on the binary matrix. For this purpose we have used the Brillouin and Raman scattering techniques. The identification of the structural units of the glass can be made qualitatively from the analysis of the high frequency part of the Raman spectra, while Brillouin experiments can give connection between the acoustical and structural properties. Brillouin results are also of first interest for the interpretation of the so-called Boson peak which dominates the low part of the Raman spectra. Following the Martin and Brenig model (4) the structural correlation range, which reflects the average size of the boron oxygen edifices, can be deduced. High Raman data. The amorphous B203 x M20 systems have already been widely studied by Raman spectroscopy 11,5,6). This spectrum is dominated by two lines at 806 cm and 780-765 cm respectively due to the breathing vibration of boroxol and of six-membered rings containing BO., units (di tri tetraborate groups). By a systematic study of all alcali borate glasses (and also T£20 containing glasses) we have found different laws for the progressive disappearance of the boroxol 806 cm line with increasing values of x : the larger the ionic radius of M, the earlier the 806 cm line disappears. This is compatible with an Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19829108 C9-542 JOURNAL DE PHYSIQUE increase of the dimensions of the borate edifices with increasing s izes of M+ and can be interpreted from stoechiometric reasons by the dominant formation of tribor a t e groups i n the case of B2O3-x Li20 , and tetraborate groups for B203 X Cs20 (0 0.2) 20 does not exceed the dimension of one six-membered ring (this is for instance the case of tr iborate groups). A s the mass of the atom increases, 20. also increases ; t h i s agrees with the formation of borate groups containing more than one six-membered rings. A detailed analysis of these resul ts w i l l be published i n a subsequent forthcoming paper. Fig.2 Low Raman s p e c t r a of Fig .3 S t r u c t u r a l c o r r e l a t i o n range B203-0 ,25 M20 g l a s s e s deduced from the Martin-Brenig t h e o r e t i c a l f i t s wi th Martinmodel.

CONNECTION BETWEEN THE LOW TEMPERATURE ACOUSTIC PROPERTIES AND THE GLASS TRANSITION TEMPERATURE OF FLUORIDE GLASSES

The variations of the velocity and the absorption of longitudinal and transverse acoustic waves have been measured in three fluoride glasses in the temperature range 0.1 K to 1.5 K. The density of states of two level systems (TLS) and the TLS - phonon coupling constants have been determined. The TLS density of states has been found to be inversely proportional to the glass transition temperature.

On the propagation of linear transverse acoustic waves in isotropic media with mechanical relaxation phenomena due to viscosity and a tensorial internal variable

The propagation of linear transverse acoustic waves in isotropic media in which mechanical relaxation phenomena occur was considered in a previous paper. In particular expressions for the velocity and attenuation of the waves were obtained and the limiting cases of waves with high and low frequencies were discussed. In the present paper we investigate the propagation of linear transverse acoustic waves in Poynting-Thomson, Jeffreys, Maxwell, Kelvin-Voigt, Hooke and Newton media. We show that the dispersion relations for these waves may be considered as degeneracies of the dispersion relation which we derived in the general case of a viscoanelastic medium with memory. In particular we investigate the explicit dependence of the dispersion relations on the thermodynamic parameters and the phenomenological coefficients.

On asymmetric propagation on transverse acoustic waves near the structural phase transition in RbH 3(SeO 3) 2

Recently ultrasonic measurements of the RbH 3(SeO 3) 2 crystal have shown that a transverse acoustic wave propagating along the modulation axis of the incommensurate structure ( c-axis) and polarized along the polar axis ( b-axis) exhibits greater temperature anomalies of its velocity and damping than a wave propagating along the b-axis and polarized along the c-axis. The possible explanation of this experimental result is given on the basis of the Landau theory.

Transverse Acoustic Waves in Pulsed Lasers

Transverse acoustic waves in pulsed lasers result from nonuniform pumping transverse to the flow direction. This theoretical study is based on linear acoustics and disregards hot/cold gas interfaces. First, transverse waves in an infinite parallel hard-walled duct are considered, in which case cavity medium inhomogeneity typically decays as t ~ ' / 2 . An idealized treatment is next given to show that exponential decay can be expected with an anode absorber. There is an optimum absorber resistivity and improved attenuation rate results with increased backing volume. Tilted sidewalls are the final topic. Decay is again exponential, and rapid attenuation requires fairly large tilt angles. Examples are chosen to apply to CO2 electric discharge, chemical, and excimer lasers.

On the propagation of linear transverse acoustic waves in isotropic media with mechanical relaxation phenomena due to viscosity and a tensorial internal variable: I. General formalism

In this paper we consider the propagation of linear transverse acoustic waves in isotropic media in which mechanical relaxation phenomena occur. It is assumed that the irreversible mechanical processes in the medium are due to viscosity and to changes in a tensorial internal variable and that these processes can be described with the aid of non-equilibrium thermodynamics. The viscous flow phenomenon is analogous to the viscous flow of ordinary fluids. In particular we investigate the velocity and attenuation of the waves and we consider the limiting cases of waves high and low frequencies. For high frequencies we obtain expressions for the phase velocity and attenuation which are analogous to those for viscous fluids and it is seen that the tensorial internal variables does not influence the propagation of waves. If the frequencies are sufficiently low, the expression for the phase velocity is analogous to the expression for the phase velocity in purely elastic media, while the damping is influenced by both irreversible phenomena and the imaginary part of the complex wave number is proportional to the square of the frequency.

Ultrasonic investigation of phase transitions in K2SnCl6

The velocities and the attenuation of ultrasonic waves have been investigated as a function of temperature (255K≦T≦350K) for the cubic phase of K2SnCl6 which undergoes a structural transition atTc1≃263K. An anomalous decrease of the shear stiffness constantc′=1/2(c11−c12) of about 30% between room temperature andTc1 is found in this cubic high temperature phase whenTc1 is approached from above. Whereas the softening ofc′ extends over a substantial temperature range (about 50 K), the other shear constantc44 shows only a weak decrease, which is an order of magnitude smaller and restricted toT−Tc1≦10 K. NearTc1, a strong increase occurs in the attenuation of the shear acoustic wave propagated along the [111] direction, while such an anomalous attenuation is not observed for the transverse acoustic wave propagated along [100]. Furthermore, atTc1 a hysteresis is detected for the longitudinal sound wave velocityvL[100], which is restricted to the temperature region 262K≦T≦263.5 K. In addition, the room-temperature elastic constants of (NH4)2SiF6 and the hydrostatic pressure derivatives of the elastic constants of K2SnCl6 and (NH4)2SiF6 at room-temperature are presented and discussed in terms of mode softening behaviour.

Diffuse Umklapp scattering in amorphous metals

It is shown that the short-wavelength collective excitations recently detected in the metallic glass Mg0.7Zn0.3 using inelastic neutron scattering arise from a diffuse Umklapp scattering from transverse acoustic waves.