掺铑BaTiO3单晶场致应变特性的研究

系统地研究了掺铑的BaTiO₃单晶在老化后的场致应变性能.研究发现，晶体的场 致应变随老化时间的增加而增大，在老化27天后，在300V/mm的电场下，其双向场致应变可达1.11％；在较小的测试频率下（0.01Hz）也可得到0.95％的可逆的巨大的单向场致应变，在低频范围内，晶体的单向场致应变随测试频率增大而减小；研究晶体老化后的电滞回线，发现其 形状类似于蜂腰磁滞回线.实验结果表明，对BaTiO₃单晶掺杂铑元素可以大大改 善其电致伸缩性能，可能产生新的在超大应变及非线性驱动器中的应用. 关键词： 3单晶')" href="#">BaTiO₃单晶 掺铑 场致应变 老化     

Dielectric response in ferroelectric BaTiO3

The far-infrared optical and dielectric properties of ferroelectric perovskite titanate powder BaTiO₃ are reported. The terahertz time-domain spectroscopy (THz-TDS) measurement reveals that the low frequency dielectric response of BaTiO₃ is closely related to the lowest pair of transverse optical (TO) and longitudinal optical (LO) modes near at 180 cm⁻¹, which is verified by Raman spectroscopy. This result provides a better understanding of the relation of low-frequency dielectric function with the optical phonon mode for ferroelectric materials. Combining terahertz TDS with Raman spectra, the overall low frequency optical phonon response of BaTiO₃ is presented in an extended spectral range from 6.7 to 1200 cm⁻¹.     

Characterization of optical and nonlinear properties of periodically-poled RbTiOAsO4 in the mid-infrared range via difference-frequency generation

Tunable mid-infrared coherent radiation (3.25- 3.7 μm) is generated by quasi-phase-matched difference frequency generation in a multi-grating periodically-poled RbTiOAsO₄ crystal. The spontaneous polarization and coercive field of flux-grown RbTiOAsO₄ are determined by polarization switching measurements. The nonlinear interaction enables us to explore the optical and nonlinear properties of this material in the mid-infrared range, where data is scarce. The measurements are used to derive a mid- infrared corrected dispersion equation for n_z in RbTiOAsO₄. This equation is in excellent agreement with previously published measurements of nonlinear interactions in periodically-poled RbTiOAsO₄. The measured wavelength and temperature bandwidths are ≈48 nm cm and ≈29 °C cm, respectively. A relatively high temperature tuning slope of the phase-matched idler wavelength, -1.27 nm/°C, is measured. This may be useful for realizing temperature-tuned nonlinear devices. Received: 30 March 2000 / Revised version: 9 May 2000 / Published online: 30 June 2000     

The ferroelectric field effect on the two-dimensional electron gas at LaAlO3/SrTiO3 (001) interface: Insights from first principle simulations

We perform first-principles calculations to explore the possibility of tuning the two-dimensional electron gas at the LaAlO₃/SrTiO₃ (001) interface through BaTiO₃ substrate. A metal-to-insulator transition is found at the interface as the polarization of BaTiO₃ reverses. Through the potential analysis of the LaAlO₃/SrTiO₃/BaTiO₃ superstructure, we find that the intrinsic electric field of LaAlO₃ is significantly suppressed as the polarization points away from the LaAlO₃/SrTiO₃ interface, while it is enhanced with the polarization pointing to the interface. The ferroelectric field control of the intrinsic electric field, and therefore the electronic reconstructions at the interface, originating from the screening of polarization charges, opens the way to the development of novel nanoscale electronic devices.     

Nonlinear scattering in BaTiO3 induced by two orthogonally polarized waves

A new nonlinear scattering effect is described which is induced by the simultaneous action of ordinary and extraordinary waves impigning on a BaTiO₃ crystal in the plane perpendicular to the c-axis. The scattered light of ordinary polarization propagates along a circular cone and the light intensity on this cone is nonuniform. We present a model that describes the experimental observations rather well, including phase matching conditions and the unusual intensity distribution of the scattered light.     

BaTiO3和Ce:BaTiO3晶体极性声子和电磁激元的喇曼散射研究

从声子-电磁激元频率色散关系的普遍公式出发,推导出了单轴晶体的Merten方程和电磁激元的频率色散关系。测量了BaTiO₃和Ce:BaTiO₃晶体的简正模和斜声子的喇曼散射谱,并根据Merten方程,拟合出了斜声子的方向色散曲线;记录了A₁类电磁激元在不同波矢值下的喇曼谱,观察到其频率色散现象.根据以上结果,对A₁(TO)模喇曼谱中两个宽的非对称峰的归属和BaTiO₃晶体的结构相变机制进行了讨论;计算出了这两种晶体的受夹介电常数;分析了掺Ce对BaTiO₃晶体结构的影响。 关键词：     

1-3型纳米多铁复合薄膜中电场诱导的磁化研究

运用Landau-Devonshire热力学唯像理论,考虑铁电相和铁磁相的电致伸缩、磁致伸缩效应以及产生于铁电/铁磁和薄膜/基底界面的弹性应力作用,两次重整介电和磁作用系数得到了这种多铁系统在Landau自由能函数下的本征二次方磁电耦合形式,从而研究了外延1-3型纳米多铁复合薄膜中极化、磁化随薄膜厚度、温度的变化以及该薄膜中外加电场诱导的磁化变化.结果表明薄膜平面内的应压力的弛豫使得磁化强度和极化强度随薄膜厚度的增加而减少,外加电场不仅能诱导铁电相极化场翻转,而且由于铁电和铁磁相界面竖直方向的弹性耦合导致 关键词： 多铁 磁电效应 磁致伸缩 薄膜     

Anisotropic electrodynamics of low dimensional metals: Optical studies of (TMTSF)2ClO4

Optical experiments are reported for the metallic state of the linear chain compound (TMTSF)₂ClO₄. For the electric field polarized both along the highly (a) and intermediately (b ) conducting directions, a zero energy (ZE) mode and a finite energy mode (FE) are observed. The large anisotropy in the spectral weight of the FE mode is consistent with the band structure, however the spectral weight of the ZE mode is surprisingly isotropic. In the least conducting (c ^*) direction, the low frequency optical conductivity along with the dc conductivity indicate the presence of a (small) Drude component only at temperatures below 10 K. These observations provide evidence for a correlation induced semimetallic state, with a 3D to 2D crossover with increasing temperature. Received 20 May 1999     

Studies of the third-order nonlinear optical susceptibility for InxGa1−xN/GaN cylinder quantum dots

The resonant third-order susceptibilities at various directions (both parallel and vertical to Z-axis) in self-assembled quantum dots (QDs) have been investigated. The nonlinear susceptibilities associated with the intraband transition in the conduction band are theoretically calculated for wurtzite In_xGa_1−xN/GaN-strained cylinder QDs. The confined wave functions and energies of electrons in the dots have been calculated in the effective-mass approximation by solving the 3D Schrödinger equation, in which a strong built-in electric field effect due to the piezoelectricity and spontaneous polarization has been taken into account. Furthermore, it is shown that the magnitude and the resonant position of the nonlinear susceptibility χ⁽³⁾(3ω) strongly depend on the dots’ size as well as size distribution.     

Structure, dielectric and ferroelectric properties of highly (1 0 0)-oriented BaTiO3 grown under low-temperature conditions

The highly (1 0 0)-oriented BaTiO₃ thin films were fabricated on LaNiO₃(1 0 0)/Pt/Ti/SiO₂/Si substrates under low-temperature conditions. Substrate temperatures throughout the fabrication process remained at or below 400 °C, which allows this process to be compatible with many materials commonly used in integrated circuit manufacturing. X-ray diffraction data provided the evidence for single BaTiO₃ phase. Field-emission scanning electron microscopy was used to study the columnar structure of the films. The dielectric properties as a function of frequency in the range of 1 kHz to 1 MHz was obtained. The room temperature remanent polarization (2P_r) and coercive field were found to be ∼5 μC/cm² and 50 kV/cm, respectively. The BTO film maintains an excellent fatigue-free character even after 10⁹ switching cycles.     

钽掺杂对钛酸钡导热性能影响的研究

利用光热检测技术测量了钛酸钡材料的导热性能，得到了不同成型压力、烧结温度以及不同 掺杂量下的钛酸钡材料的热扩散率.研究了钽掺杂对钛酸钡材料导热性能的影响，发现了钽 元素掺杂量小于1.5mol%时，钛酸钡材料的热扩散率随掺杂量的增加而增大，当钽元素掺杂 量大于1.5mol%时，热扩散率随掺杂量的增加而减少.对钛酸钡材料的导热性能做了进一步的 分析. 关键词： 光热检测 钛酸钡 导热性能 钽掺杂     

Photorefraction in the ultraviolet: Materials and effects

Doped as well as nominally pure crystals of Lithium Niobate (LiNbO₃), -Arginine Phosphate (LAP), Lithium Iodate (LiIO₃), Potassium Dihydrogen Phosphate (KDP), Lithium Formate (LFM), Beta-Barium Borate (BBO), and lithium tetra borate were grown and investigated for photorefractive effects at ultraviolet wavelengths down to 333 nm. In nominally undoped LiNbO₃ crystals strong beam coupling effects were observed. In contrast to the visible we revealed a diffusion-dominated charge transport mechanism based on holes, and a low photovoltaic field in the order of 550 V/cm. With such a crystal we investigated the modulation transfer function of a lensless image projection system based on a phase conjugation scheme. A spatial frequency response beyond 2800 line pairs per millimeter was observed. Photorefractive beam coupling was also obtained in LiIO₃. Light-induced scattering was detected in iron-doped LiIO₃ whereas as-grown LAP material did not exhibit any observable photorefractive effects. However, 100 kV X-ray irradiation seems to induce material defects which can lead to weak light-induced scattering at 351 nm. In all other above-mentioned materials, doped as well as undoped, light-induced scattering could not be observed. On the other hand, this is appreciated in all the applications where the crystals are used as nonlinear material for optical frequency conversion.     

Combination of spontaneous polarization plasma and photocatalyst for toluene oxidation

In this paper, we report toluene destruction using a spontaneous polarization plasma and photocatalyst reactor in air at atmospheric pressure and room temperature. A spontaneous polarization material (BaTiO₃) and photocatalyst (TiO₂) were added to the plasma system simultaneously. Three types of catalyst, i.e., TiO₂, BaTiO₃, or TiO₂/BaTiO₃, were used for toluene removal. The catalyst carrier, type, and amount were important factors in the toluene removal efficiency. The specific energy density and energy yield during the discharge process were investigated. The toluene removal efficiency increased when a spontaneous polarization plasma was combined with the photocatalyst. In terms of toluene removal efficiency, the activity order was TiO₂/BaTiO₃ > BaTiO₃ > TiO₂ > none. Large amounts of BaTiO₃ in the TiO₂/BaTiO₃ catalyst gave slightly better conversion. The TiO₂/BaTiO₃ catalyst not only enhanced the toluene removal efficiency, but also saved energy, making it useful for industrial applications.     

Electromechanical-induced antiferroelectricben ferroelectric phase transition in PbLa(Zr,Sn,Ti)O3 ceramic

Antiferroelectric—ferroelectric (AFE—FE) phase transition in ceramic Pb_0.97La_0.02(Zr_0.75Sn_0.136Ti_0.114)O₃ (PLZST) was studied by dielectric spectroscopy as functions of frequency (10²—10⁵ Hz) and pressure (0—500 MPa) under a DC electric field. The hydrostatic pressure-dependent remnant polarization and dielectric constant were measured. The results show that remnant polarization of the metastable rhombohedral ferroelectric PLZST poled ceramic decreases sharply and depoles completely at phase transition under hydrostatic pressure. The dielectric constant undergoes an abrupt jump twice during a load and unload cycle under an electric field. The two abrupt jumps correspond to two phase transitions, FE—AFE and AFE—FE.     

Colossal magnetostriction effect in HoMn2O5

We have investigated the detailed field and temperature dependence of the dielectric constant, electric polarization, magnetization and magnetostriction in orthorhombic HoMn₂O₅ single crystals. HoMn₂O₅ displays incommensurate antiferromagnetic ordering below 39 K, becoming commensurate on further cooling. The commensurate-incommensurate transition takes place at low temperatures. The inherent magnetic frustration in this material is lifted by a small lattice distortion, primarily involving shifts of the Mn³⁺ cations and giving rise to a canted antiferroelectric phase. Colossal magnetostriction effect was observed and a novel phase transition diagram was build.     

Fully relativistic calculations of the L2,3-edge XANES spectra for vanadium oxides

Fully relativistic multielectron method based on the numerical solution of the Dirac equation was used to calculate the L_2,3-edge X-ray absorption near edge structure (XANES) spectra of VO₂, V₂O₃, and V₂O₅ crystals. The key-points of the method are: i) usage of the molecular orbitals (MO); ii) absence of any fitting parameters; iii) wide area of application: to any ion in any symmetry; iv) possibility of numerical analysis of the MO composition. The calculated spectra are in a satisfactory agreement with experimental data available in the literature, including the absolute values of the transitions energy, the shape of the absorption bands, and polarization dependence. The assignment of the absorption bands in terms of the electronic configurations was done. The structure of the absorption bands is attributed to the splitting of the vanadium p- and d-orbitals; the magnitude of this splitting is estimated from the spectra. Covalency effects were considered for all hosts; it was shown that the contribution of the oxygen wave functions increases with increasing the vanadium oxidation state. Dependence of the relative positions of the vanadium 3d and oxygen 2p levels and energies of the “ligand–metal” charge transfer transitions on the vanadium oxidation state was analysed.     

由BaTiO3晶体结构相变时的介电特性研究其电场作用下的偶极子偏转路径

在不同频率和偏置电场下测量了BaTiO₃晶体从三方相到正交相再到四方相相变过程中的介电温谱.基于BaTiO₃晶体在电场作用下的偶极子偏转假设和介电特性实验结果,提出BaTiO₃各结构相在电场作用下的偶极子偏转路径可以由其相邻相的介电常数随温度的变化特性表现出来.推断出各结构相的偶极子偏转路径,以及偏置电场对偶极子偏转路径的影响. 关键词： 3晶体')" href="#">BaTiO₃晶体 介电特性 结构相变 偶极子偏转路径     

Cascaded frequency doubling and electro-optic coupling in a single optical superlattice

Frequency doubling and electro-optic (EO) coupling are cascaded in a single optical superlattice due to simultaneous modulation of nonlinear and EO coefficients. The coupling equations are deduced and analyzed, and simulations in both periodic and quasi-periodic structures are presented. The results show that both polarization and magnitude of the second harmonic can be manipulated by an external DC electric field, which is useful when simultaneous frequency conversion and signal tuning are desired.This revised version was published online in August 2005 with a corrected cover date.     

Multiwave-pumped mirrorless parametric oscillation in BaTiO3

We report on the observation of mirrorless oscillation in photorefractive BaTiO₃ pumped by two pairs of two nearly counterpropagating light waves, each of them containing an ordinary and an extraordinary component of polarization. The oscillation waves are located on a cone with an apex angle defined by the phase-matching conditions of this process.     

Co:BaTiO3/Si(100)纳米复合薄膜制备、微结构及其紫外光电子能谱研究

采用脉冲激光气相沉积(PLD)方法,在Si(100)晶面上制备了Co:BaTiO₃纳米复合薄膜.采用X射线衍射(XRD)结合透射电镜(TEM)方法研究了两种厚度Co:BaTiO₃纳米复合薄膜的晶体结构,当薄膜厚度约为30 nm时,薄膜为单一择优取向;当薄膜厚度约为100nm时,薄膜呈多晶结构.原子力显微镜(AFM)分析表明,当膜厚为30nm时,薄膜呈现明显的方形晶粒.采用紫外光电子能谱(UPS)研究了Co的价态和Co:BaTiO₃纳米复合薄 关键词： 3')" href="#">BaTiO₃ 纳米复合薄膜 紫外光电子能谱