Electric field effects on the dielectric and acoustic anomalies of Pb[(Mg1/3Nb2/3)0.83Ti0.17]O3 single crystals studied by dielectric and Brillouin spectroscopies

The effect of the electric field on the dielectric and acoustic properties of Pb[(Mg_1/3Nb_2/3)_0.83Ti_0.17]O₃ single crystals was investigated as functions of temperature and the electric field strength. The dielectric constant and the acoustic mode behaviors exhibited typical relaxor behaviors when there was no bias field. The longitudinal acoustic mode showed splitting under a moderate electric field of 1 kV/cm applied along the [001] direction, indicating coexistence of macroscopic/mesoscopic ferroelectric states and relaxor states. Further increase in the electric field up to 2 kV/cm induced a clear ferroelectric phase transition, which became smeared out due to the proximity of the electric field to the critical point. The electric field-temperature phase diagram of Pb[(Mg_1/3Nb_2/3)_0.83Ti_0.17]O₃ was suggested based on the observed field-induced changes in the dielectric and the acoustic properties.     

Elastic stiffness constants and acoustic symmetry of LiY0.5Tb0.5F4

Measurements of ultrasound wave velocities between 4.2 and 293 K have been used to determine the temperature dependences of the seven adiabatic elastic stiffness tensor components of the laser host scheelite structure fluoride LiY_0.5Tb_0.5F₄. The sign of C₁₆ is negative, as found previously for other oxide and fluoride scheelites; therefore for LiY_0.5Tb_0.5F₄ the positions of the acoustic symmetry axes in the XY plane have the same sense as those of the other scheelites. The k and γ axes of acoustic symmetry lie at +31° and + 76° from the + X axis. Transformation of the elastic stiffness constants to a basis comprised of two acoustic symmetry axes together with the +Z axis enables a detailed comparison of the elastic behaviour of LiY_0.5Tb_0.5F₄ with those of other scheelite crystals.     

Temperature-dependent Brillouin scattering studies of surface acoustic modes in Nd0.5Sr0.5MnO3

Brillouin scattering experiments are carried out to study the surface acoustic waves in Nd_0.5Sr_0.5MnO₃ as a function of temperature in the range of 40-300 K covering the metal-insulator and charge-ordering phase transitions. The surface modes include surface Rayleigh wave, pseudo-surface acoustic wave (PSAW) and high velocity PSAW. The observed softening of the sound velocities for the surface modes below paramagnetic to ferromagnetic transition, T_c is related to the softening of the C₄₄ elastic constant. The subsequent hardening of the sound velocity below the charge ordering transition temperature T_co is attributed to the coupling of the acoustic phonon to the charge ordered state via long range ordering of the strong Jahn-Teller (JT) distortion.     

Tunable Ba0.5Sr0.5TiO3 film bulk acoustic resonators using SiO2/Mo Bragg reflectors

Tunable and switchable Ba 0.5 Sr 0.5 TiO 3 film bulk acoustic resonators（FBARs） based on SiO 2 /Mo Bragg reflectors are explored,which can withstand high temperature for the deposition of Ba x Sr 1 x TiO 3（BST） films at 800 C.The dc bias-dependent resonance may be attributed to the piezoelectricity of the BST film induced by an electrostrictive effect.The series resonant frequency is strongly dc bias-dependent and shifts downwards with dc bias increasing,while the parallel resonant frequency is only weakly dc bias-dependent and slightly shifts upwards at low dc bias（ 45 V） while downwards at higher dc bias.The calculated relative tunability of shifts at series resonance frequency is around 2.3% and the electromechanical coupling coefficient is up to approximately 8.09% at 60-V dc bias,which can be comparable to AlN FBARs.This suggests that a high-quality tunable BST FBAR device can be achieved through the use of molybdenum（Mo） as the high acoustic impedance layer in a Bragg reflector,which not only provides excellent acoustic isolation from the substrate,but also improves the crystallinity of BST films withstanding higher deposition temperature.     

Inelastic neutron scattering from transverse acoustic modes in K2SnCl6

In cubic K₂SnCl₆ the dispersion curve für q q; [110] of [1$\text{1}$0] polarized acoustic phonons has been measured at three temperatures near the phase transition temperature T_c1. The acoustic branch shows no temperature dependence in the low wave vector region and stiffens slightly near the X-point of the fcc-Brillouin zone as the temperature approaches the phase transition T_c1= 262 K from above. The results support a previously developed model on acoustic anomalies in this compound.     

Acousto-induced structural change in amorphous As2S3

The acoustic flux injection method was applied to amorphous As₂S₃. The velocity and the attenuation constant for shear wave at ～ 100MHz were measured through the observation of the Brillouin scattering of the light beam from a He-Ne laser. The optical transmission around absorption edge was found to change after the injection of acoustic fluxes. It was also found that the sound velocity decreased with increasing injection time of acoustic fluxes and the amount of the change of the sound velocity reached ～ 20% after 10⁵ injections. The changes in the optical transmission and the sound velocity tended to be erased by annealing below the glass transition temperature. These phenomena are considered to be due to structural changes caused by the injection of strong acoustic fluxes.     

(Hf0.5Zr0.5V2)Hx的声子谱与超导性的关系

本文报道了用Be过滤探测器谱仪对C-15相的(Hf_0.5Zr_0.5V₂₎H_x等五种样品的声子谱的测量。观察到了它们的声子谱随含氢量而变化以及声学支有规则的软化现象。表明(Hf_0.5Zr_0.5V₂₎H_x的T_c随x的变化,主要是声学支的贡献,声学文软化有利于T_c的提高,而光学支“软化”可能会抑制超导性。 关键词：     

Brillouin scattering investigation of paraelectric KH2PO4 under applied uniaxial stress

The Brillouin scattering spectra of KH₂PO₄ under an applied uniaxial stress have been studied in the neighborhood of the ferroelectric transition. Dependence of shear acoustic phonon on the uniaxial stress is similar to dependence on electric field. The acoustic phonon is overdamped near T_c, but become underdamped under the applied shear stress. In the case of ΔT(= T — T_c) < ～ 0.05 K, application of stress caused a transition not to have any soft acoustic phonon.     

Li2O-(LiCl)2-B2O3-Al2O3系统玻璃的声学性质

本工作测量了Li₂O-(LiCl)₂-B₂O₃-Al₂O₃系统玻璃的密度、超声速,计算了玻璃的绝热压缩系数,从声学性质分析了玻璃骨架结构随组成的变化,为研究玻璃的离子导电性提供了方法和分析的依据。 关键词：     

Phonon-phonon interactions in (Lu, Y)Ni2B2C

The temperature dependence of the Δ₄ acoustic and optic mode, measured at q=(0.5,0,0) in LuNi₂B₂C, YNi₂B₂C were extended to 1000 K and new measurements on the mixed compound, Y_0.5Lu_0.5Ni₂B₂C, were undertaken to explore the mode coupling in these materials. The temperature behavior of each is different and cannot be explained by a simple mode coupling scheme of the acoustic and optic modes.     

Acoustic properties of multiferroic PbFe1/2Ta1/2O3

The longitudinal acoustic wave velocity and attenuation in PbFe_1/2Ta_1/2O₃ ceramics have been measured by pulse-echo technique in the temperature range from 4.2 to 530 K. The anomalies observed in the sound velocity and attenuation behavior versus temperature were correlated with Burns temperature, temperature range of the coexistence of relaxor ferroelectric and antiferromagnetic states, and a suggested second antiferromagnetic phase transition at low temperatures.     

Electronic structure and the infrared absorption and Raman spectra of the semiconductor clusters C24, B12N12, Si12C12, Zn12O12, and Ga12N12

The optimized configurations, electronic structures, charge transfers, band gaps, total energies, cohesive energies, electron density maps, infrared absorption spectra, Raman spectra, and relevant modes of natural acoustic vibrations for the semiconductor clusters C₂₄, B₁₂N₁₂, Si₁₂C₁₂, Zn₁₂O₁₂, and Ga₁₂N₁₂ are calculated using the ab initio Hartree-Fock method in the 6–31G basis set. Original Russian Text ? V.V. Pokropivny, L.I. Ovsyannikova, 2007, published in Fizika Tverdogo Tela, 2007, Vol. 49, No. 3, pp. 535–542.     

Brillouin scattering in KH3 (SeO3)2 above the transition temperature

The Brillouin scattering measurement in KH₃(SeO₃)₂ above the transition temperature shows a large anomaly in hypersonic velocity of the transverse wave with the wave vector q = [010] and the polarization ξ = [001], which indicates acoustic phonon softening.     

The magnetic field dependence of the structural transition temperature in La3S4 and La3Se4

The magnetic field dependence of the structural transition temperature T_m from the cubic to the tetragonal phase has been determined for single crystals of La₃S₄ and La₃Se₄. The observed field dependence of T_m can be accounted for by the band Jahn-Teller model of the coupling of an e_g-band to the shear mode of the cubic lattice without invoking any coupling to acoustic or optical phonons.     

Elastic behaviour under pressure of the cluster compound (Ag6Ge4P12)Ge6

The elastic stiffness constants of the cluster compound (Ag₆Ge₄P₁₂)Ge₆ have been measured by the ultrasonic pulse-echo overlap technique and are found to conform quite closely with those of zincblende structure compounds. The hydrostatic pressure dependences of the elastic constants and also the third-order elastic constants have been measured. It is found that, unlike the zincblende structure compounds, this compound does not show any tendency towards shear mode softening under pressure, all the long wavelength acoustic mode Grüneisen gammas being positive.     

Light scattering study of ferroelastics Hg2Br2

Brillouin and Raman scattering spectra of the soft modes in Hg₂Br₂ have been measured using triple pass Fabry-Perot interferometers. The temperature dependence of the coupled soft optical and acoustic modes are analyzed by use of the thermodynamic potential and the equations of motion for the coupled oscillators. These two methods have given the same result for explaining the elastic anomaly of Hg₂Br₂ crystals below the transition temperature.     

Crystal growth and dielectric, piezoelectric and elastic properties of Ca3TaGa3Si2O14 single crystal

Single crystals of Ca₃TaGa₃Si₂O₁₄ (CTGS) were successfully grown from stoichiometric melts by the conventional Czochralski technique. The relative dielectric constants, the piezoelectric strain constants and the elastic compliance constants of CTGS single crystal have been determined by an electric bridge and resonance-antiresonance method. At room temperature, the two piezoelectric strain constants d₁₁ and d₁₄ are −4.58×10⁻¹² coulombs per newton (C/N) and 10.43×10⁻¹² coulombs per newton (C/N), respectively. The velocities of the bulk acoustic wave are also calculated.     

The elastic constants of V2O3 in the insulating phase

The initial slopes of the acoustic phonon dispersion curves in (V_0.98Cr_0.02)₂O₃ have been measured at room temperature in several of the high symmetry directions by inelastic neutron scattering. From these data several sound velocities and four independent elastic constants have been determined. Although the Cr doped specimen is in the insulating phase and pure V₂O₃ is metallic, these results are in good agreement with recent data (1) obtained by ultrasonic measurements on pure V₂O₃.     

Anelastic effects in (AgI)x(Ag2O·B2O3)1−x superionic glasses

We present here the first measurements of acoustic absorption in (AgI)_x(Ag₂O·B₂O₃)_1?x superionic glasses at ultrasonic frequencies (5–45 MHz) and in the 80–434 K temperature range. The attenuation shows, at decreasing temperature, an unusually high peak which seems to be attributed to a thermally activated relaxation process. A possible microscopic explanation of this anomaly is proposed, in connection with the presence of mobile ions in those materials.     

Brillouin scattering investigation of the structural phase transition of TlCdF3 and RbCaF3

The elastic constants of the fluoroperovskites TlCdF₃ and RbCaF₃ have been investigated by means of Brillouin scattering. Elastic and attenuation anomalies have been observed very near the phase transition temperature for longitudinal and transverse acoustic waves.