Surface acoustic waves interaction with twin structure in the LiNbO3 crystal

This paper reports a scanning electron microscopy study of the surface acoustic waves interaction with twin structure in the LiNbO₃ crystal. The twin was formed spontaneously in the process of the LiNbO₃ crystal growth. We investigated the surface acoustic waves reflection and refraction on the twin structure. Also, we demonstrate the shift of the surface acoustic wave potential contrast on the twin walls.     

Waveguide properties of regular domain structure in LiTaO3 crystal

This paper reports a scanning electron microscopy study of the surface acoustic wave interaction with regular domain structure in LiTaO₃ crystal. The regular domain structure was formed by thermoelectrical treatment after growth. The process of the surface acoustic wave propagation along domain structure and waveguide properties of the domain structure were investigated.     

Preparation of Li2B4O7 Films with Preferential Orientation by Sol–Gel Method

Li₂B₄O₇ films, a promising material for surface acoustic wave devices, were prepared by the sol—gel method using metal alkoxide precursors as starting materials. The Li₂B₄O₇ films on silicon (100) and (111) single crystals prepared from a coating solution to which acetic or hydrochloric acid was added were highly oriented along the (122) plane, whereas those without acid additive were randomly oriented. The results were interpreted based on the basic sol-gel chemistry and the lattice matching between the film and substrate.     

Surface acoustic wave interactions with regular domain structures in LiNbO3 crystals

This paper reports a scanning electron microscopy study of the interaction between surface acoustic waves and ferroelectric domain structures in LiNbO₃ crystals. The domains were formed by thermoelectric treatment after growth. We investigated both the surface acoustic wave propagation across the domain structure and the reflection phenomena on the domain walls.     

An investigation of (Na0.5K0.5)NbO3–CaTiO3 based lead-free ceramics and surface acoustic wave devices

Lead-free (Na_0.5K_0.5)NbO₃ ceramics doped with CaTiO₃ (0–3 mol%) have been prepared by the conventional mixed oxide method in this paper. All of the CaTiO₃ doped (Na_0.5K_0.5)NbO₃ specimens do not deliquesce as exposed to water for a long time. The samples are characterized by X-ray diffraction analysis, Raman scattering spectra, scanning electron microscopy, and atomic force microscopy. The dielectric, piezoelectric and ferroelectric properties are also investigated. The results show that the addition of CaTiO₃ is very effective in preventing the deliquescence and in improving the electric properties of (Na_0.5K_0.5)NbO₃ ceramics. Finally, surface acoustic wave devices based on lead-free ceramics have been successfully fabricated and their characterization is presented.     

Piezoelectricity in the Field-Induced Ferroelectric Phase of Lead Zirconate-Based Antiferroelectrics

The piezoelectric characteristics were investigated in the field-induced ferroelectric phase of the antiferroelectric Pb_0.99 Nb_0.02[(Zr_0.6Sn_0.4) _{1 − y} Ti _y ]_0.98O₃ family. The electromechanical coupling factors k _p and k _t were measured, and the piezoelectric anisotropy was calculated. The piezoelectricity was controlled easily by the applied electric field pulse. The large piezoelectric anisotropy of these materials in comparison to that of conventional PZT piezoelectric materials makes them very applicable for ultrasonic probes and surface acoustic wave filters.     

Use of LINbO3 for Design of Device-type Catalysts with Activity Controllable Functions

A poled ferroelectric LiNbO₃ single crystal with high spontaneous polarization was employed as a catalyst support, and the static and dynamic effects of the polar substrate surfaces on the adsorptive and catalytic properties of thin film catalysts deposited were shown. For the static effect, it was demonstrated that the surface conductivity of copper and metal-free phthalocyanine films increased by the adsorption of NO gas, to a larger extent, when the substrate was the negative polar surface, compared to the positive one. The role of the polar substrates is explained In terms of a band bending model. For the dynamic effect, the Rayleigh surface acoustic wave generated on the LiNbO₃ substrate was shown to enhance the catalytic activity for ethanol oxidation on Cu and Ag thin film catalysts deposited on the propagation path. It is proposed that the catalyst activation is mainly due to an electric Held produced. The use of poled LiNbO₃ is suggested to be effective for the development of a device-type catalyst with activity controllable functions.     

Saw determination of D4h layer on the surface of SrTiO3

Velocity of bulk and surface acoustic waves with frequencies 38, 76 and 114 MHz was measured in SrTiO₃ crystals in the phase transition region. The difference in the temperature dependences of bulk and surface waves as well as strong dispersion for surface waves are explained in terms of existence of a thin surface layer with D_4h symmetry.     

Raman spectroscopic studies on the sulfation of cerium oxide

In the present study, we have examined sulfation of cerium oxide via impregnation of (NH₄)₂SO₄, followed by heating in the temperature range of 220–720°C, using Raman Spectroscopy. Based on the SO and SO stretching frequencies in the range of 900–1400 cm⁻¹, a wide range of surface oxysulfur species and bulk cerium-oxy-sulfur species are identified. At 220°C, a mixture of (NH₄)₂SO₄ crystals, SO²⁻_4(aq) and HSO¹⁻_r(aq) is found to have formed on ceria's surface, whereas complete conversion of (NH₄)₂SO₄ to SO²⁻_4(aq) and HSO¹⁻_4(aq) occurs at 280°C. At 350°C, formation of a mixture of surface pyrosulfate S₂O²⁻_7(surf.0, consisting of two SO oscillators and a bulk type compound identified as Ce(IV)(SO₄)_x(SO₃)_2−x (0 < x < 2) have been observed. Upon introduction of moisture, the former transforms to HSO¹⁻_4(surf.), whereas the latter remains unchanged. At 400°C, only the bulk type compound can be observed. At 450°C, only Ce₂(SO₄)₃ is generated and remains stable until 650°C. Further increase in the temperature to 720°C results in the formation of CeOSO₄. The present study not only provides a more thorough understanding of the sulfation of cerium oxide at a molecular level, but also demonstrates that Raman spectroscopy is a highly effective technique to characterize sulfation of metal oxides.     

Acoustic properties of irradiated DIGLYCINE NITRATE crystals

Temperature dependencies of longitudinal acoustic wave velocity and attenuation had been measured in crystals of DIGLYCINE NITRATE (DGN), (NH₂CH₃OOH)2HNO₃, after and before ultraviolet (UV) and neutron irradiation. It was observed that radiation induced defects change dramatically the acoustic properties near the Phase Transition (PT) temperature.     

Brillouin light scattering from surface phonons in hexagonal and cubic boron nitride films

Phase velocities of surface acoustic waves in several boron nitride films were investigated by Brillouin light scattering. In the case of films with a predominantly hexagonal crystal structure, grown under conditions close to the nucleation threshold of cubic BN, four independent elastic constants have been determined from the dispersion of the Rayleigh and the first Sezawa mode. The large elastic anisotropy of up to c₁₁/c₃₃=0.1 is attributed to a pronounced texture with the c-axes of the crystallites parallel to the film plane. In the case of cubic BN films, the dispersion of the Rayleigh wave provides evidence for the existence of a more compliant layer at the substrate-film interface. The observed broadening of the Rayleigh mode is identified to be caused by the film morphology.     

长程TiO2纳米管阵列表面的超声清洗及其光催化性能

通过阳极氧化法在NH4F/乙二醇/H₂O的电解液中制备了长程TiO₂纳米管阵列。借助超声手段分别采用蒸馏水、丙酮和异丙醇作为超声介质清除了TiO₂纳米管阵列表面的集束,探讨其对TiO₂纳米管阵列光催化活性的影响。采用SEM、TG和XRD等对TiO₂纳米管阵列进行表征。结果表明,超声处理明显清除了纳米管阵列表面集束,超声介质对清洗过程有重要影响,丙酮相对于蒸馏水和异丙醇更适合作为超声介质,且超声超过30 min,纳米管阵列的光催化活性得到明显提高。     

焙烧温度对Ru/Ba-Mg(Al)O4氨合成催化剂性能影响

采用超声-沉淀-强静电吸附法制备了化学性质比较稳定的掺钡纳米镁铝复合氧化物Ba-Mg(Al)O₄,并以其为载体、Ru₃(CO)₁₂为活性组分前驱体,制备了一系列钌基氨合成催化剂。通过场发射扫描电镜、X射线衍射和N2物理吸附等表征手段,重点考察了焙烧温度对载体的物相组成和表面织构的影响。结果表明,随着焙烧温度的升高,制备的载体比表面积逐渐下降,表面碱性增强。当载体焙烧温度为780 ℃时,制备的负载型Ru/Ba-Mg(Al)O₄催化剂表现出较高的催化活性,在425 ℃、10 MPa和10 000 h^-1条件下,出口氨浓度达到49.17 mmol·(g·h)^-1。     

A study of the kinetics of the oxidative coupling of methane over a Li/Sn/MgO catalyst

The rate of reaction of methane with oxygen in the presence of a Li/Sn/MgO catalyst has been studied as a function of the partial pressures of CH₄, O₂ and CO₂ using a well-mixed reaction system which is practically gradientless with respect to gas-phase concentrations. It is concluded that the rate-determining step involves reaction of a molecule of CH₄ adsorbed on the catalyst surface with an adsorbed di-atomic oxygen species. The kinetics are consistent with a Langmuir-Hinshelwood type mechanism involving competitive adsorption of CH₄, O₂ and CO₂ on a single site. A comparison is made with previously published results for the Li/MgO material.     

Acoustic Characterization of Silica Glasses

Acoustic characterization of doped silica glasses with a GeO₂, P₂O₅, F, TiO₂, Al₂O₃, or B₂O₃ dopant having different concentrations is presented. Quantitative measurements were performed with a 225-MHz line-focus-beam scanning acoustic microscope. The acoustic velocity variation due to different dopant concentrations is given. It has been found that the Al₂O₃ dopant increases, but the other dopants decrease, the acoustic velocity as compared with that of the pure fused silica. We have also found that the fractional change in acoustic velocity is greater than that in refractive index for a given dopant concentration.     

The electrochemistry of tellurium in methylene chloride

It was found that TeCl₄ in methylene chloride (containing tetrabutylammonium perchlorate as a supporting electrolyte) is reduced to TeCl₂, Te⁰ and Te⁻² in potential applied. Two reduction waves are observed during the reduction of TeCl₄ at a platinum rde (Ep₁ = 0.08 ± 0.02 V, Ep₂ = −1.10 ± 0.02 V) due to the reduction of TeCl₄ to Te and Te⁻² respectively. A cathodic deposition of tellurium from TeCl₄ is followed by anodic stripping wave (Ep₁ = 0.42 ± 0.02 V), corresponding to the oxidation of Te to TeCl₂. It has been shown that reduction of TeCl₄, or TeCl⁻²₆ to Te causes coating of the electrode with metallic tellurium, on whose surface chloride ions are strongly bonded. It was found that when the electrolysis solution contains excess of chloride ion with respect to Te^IV the peak potentials of the cathodic waves shift to more cathodic values (Ep₁ = 0.30 ± 0.02 V, Ep₂ = −1.25 ± 0.02 V). After cathodic deposition of at least a monolayer of tellurium from such a solution two anodic waves appear (Ep₁ = 0.12 ± 0.03 V, Ep₂ = 0.24 ± 0.03 V) which are both due to the oxidation of Te to Te^II.     

Microporous Glass-Ceramics in NASICON-Type Copper(II) Titanium Phosphate

A novel porous glass-ceramic with a skeleton of a NASICON-type copper(II) titanium phosphate was prepared via the controlled crystallization of a glass and the subsequent chemical leaching of the resulting dense glass-ceramic. A volume-crystallized dense glass-ceramic comprised of CuTi₂(PO₄)₃ and Cu₃(PO₄)₂, whose surface was covered by a thin layer of CuO, was prepared by reheating a glass with a nominal composition of 50CuO20TiO₂30P₂O₅ (in mol%) in air. When the resulting glass-ceramic was leached with dilute HCl, the Cu₃(PO₄)₂ and CuO phases were dissolved out selectively, and a cuprous NASICON crystal of CuTi₂(PO₄)₃ was converted to its cupric type, CuTi₄(PO₄)₆, which was left as a skeleton of the porous materials. The specific surface area and the average pore radius of the porous glass-ceramic obtained were ∼70 m²/g and ∼7 nm, respectively. The porous glass-ceramic showed high catalytic activities for the dehydration of 2-propanol.     

Correlations between Strength and Acoustic Properties in Yttria-Stabilized Zirconia Polycrystals

The strength, bulk density, and acoustic properties of nine Y₂O₃-stabilized ZrO₂ polycrystals (Y-TZPs) were evaluated in the present study. The samples showed a strong correlation between strength and acoustic properties, a phenomenon that reflects the internal bulk structure, especially the Pore size distribution. Strength increased with a decrease in the attenuation coefficient and with an increase in the transverse wave velocity of the samples. On the other hand, the bulk density of the samples showed no clear relationship with strength. Bulk density reflects only the amount of pore volume in the test piece, whereas the acoustic properties are sensitive to defects or inhomogeneities in the microstructure. The attenuation coefficient and transverse wave velocity thus seem to be good parameters for estimating the strength of Y-TZPs.     

Thermal Expansion Anisotropy and Acoustic Emission of NaZr2P3O12 Family Ceramics

Most members of the NaZr₂P₃O₁₂ (NZP) family possess low, near zero, overall thermal expansion coefficients. However, they also exhibit anisotropy of axial thermal expansion. Some compounds have opposite anisotropy; for example, the a parameter of CaZr₄P₆O₂₄ contracts on heating and that of SrZr₄P₆O₂₄ expands, while the c parameter expands for the Ca compound and contracts for the Sr compound. The anisotropy of the axial thermal expansion of these materials is believed to induce microcracking. The acoustic emission method was employed here to detect microcracking in ceramics due to the axial thermal expansion anisotropy. Acoustic signals were observed during cooling of the Ca and Sr compounds from 500°C, and Na and K compounds from 600°C. On the other hand, no acoustic emission signal is detected in Ca_0.5Sr_0.5Zr₄P₆O₂₄ ceramics, in which the lattice parameters a and c remain nearly unchanged in the temperature range of room temperature to 500°C. Thus, a direct correlation between microcracking of ceramics and their anisotropic axial thermal expansion coefficients was established by employing acoustic emission monitoring techniques.     

MgH2型复合敏化储氢乳化炸药的制备及其爆轰性能

为了提高乳化炸药的爆炸威力,研制出了一种MgH₂型复合敏化储氢乳化炸药。该乳化炸药采用包覆后的MgH₂与玻璃微球复合敏化,两种材料分别起到含能添加剂和敏化剂的作用。通过研究“热点”数量和包覆材料对炸药爆轰性能的影响,确定了MgH₂型复合敏化储氢乳化炸药的配方。利用水下爆炸实验和猛度实验,研究了MgH₂型复合敏化储氢乳化炸药的爆轰特征参数和水下爆炸特性。实验结果表明,MgH₂型复合敏化储氢乳化炸药的铅柱压缩量为24.3 mm,达到军用炸药的猛度;与传统玻璃微球型乳化炸药相比,其水下爆炸峰值压力虽然下降了4.90%,但比冲击波能、比气泡能和总能量分别提高了7.83%、22.94%和18.32%。MgH₂型复合敏化储氢乳化炸药的猛度和做功能力得到了显著提高。