Room-temperature multiferroic properties of Co-doped KNbO3 ceramics

KNb_0.95Co_0.05O₃ (KN–Co) ceramic was prepared via a solid-state reaction method, and the effect of cobalt dopant on the structural, electric, and magnetic properties was studied. The KN–Co ceramic with polycrystalline perovskite structure exhibited ferromagnetic and ferroelectric properties simultaneously at room temperature, and the coupling of them was confirmed by a large magnetocapacitance effect (about 13%) near the Curie temperature. The possible causes for the magnetism and magnetoelectric properties are discussed.     

Electro-optical properties of superlattices

In the long-wavelength approximation, the dependence of electro-optical properties of superlattices on the mutual orientation of crystallographic axes forming the layer structure is studied. It is shown that electrooptical crystals can be used as a base for the production of layered periodic structures that are insensitive to the external electric action. The conditions for obtaining superlattices with a high electro-optical efficiency are found. The results of a numerical simulation can be used for the production of high-efficiency electro-optical materials with optimum parameters, which are required for the development of information transfer systems.     

Anisotropic self-diffraction in KNbO3

Anisotropic diffraction and self-diffraction processes in KNbO₃ crystals are investigated utilizing the large elementr ₅₁ of the electro-optic tensor. Geometrical conditions, polarization changes, phase conjugation, phase doubling and the dynamics of hologram recording are studied theoretically and experimentally. Anisotropic diffraction with equal or different frequencies for recording and reading permits the determination of photo- and dark conductivity. Further material properties are estimated on the assumption that the charge transport is governed by diffusion effects.     

Electro-optical properties of dielectric liquid microlens

We report the electro-optical properties of dielectric liquid droplets based on dielectrophoretic effect. Due to dielectric force, the surface of each droplet can be reshaped which in turn alters its focusing behaviors. Our experimental results show that a deformed droplet can recover to its original shape with a negligible hysteresis. Both amplitude and frequency of the applied voltage play important roles affecting the droplet's shape change. The rise time is mainly governed by the applied voltage: for a given frequency a higher voltage results in a faster rise time. On the other hand, the decay time is jointly determined by the interfacial surface tensions, droplet size, and viscosity of the employed liquids.     

Electro-optical properties of doped anthracene films

Electroluminescence in anthracene doped with anthraquinone (10^?3 mole%) films are presented. Films are deposited at room temperature in a vacuum of 10^?5 torr. It is observed that at constant frequency the brightness/voltage relationship follows the relation $\text{B = B}{}_0\text{exp}\text{(?b/V}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{)}$. The results show that electroluminescent brightness increases linearly with frequency. At lower frequencies green electroluminescent (EL) emission and at higher frequencies blue EL emission is observed. Similar nature for I–V and brightness/voltage relationship are found in anthracene doped with 10^?4 mole% anthraquinone.     

Electro-optical properties of excitons in polydiacetylene chains

We show how to compute the optical functions (reflectivity, transmission, and absorption) of polydiacetylene chains diluted in their monomer matrix exposed to a uniform electric field in the chain direction, in the excitonic energy region. Adopting a model electron-hole potential, we derived an analytical expression for the effective chain susceptibility, which gives the optical functions. The resulting absorption shows excitonic peaks below the gap and Franz-Keldysh oscillations above the gap. The method has been applied for a 3BCMU polydiacetylene chain, showing a good agreement with experimental spectra. Received 5 November 1998 and Received in final form 23 February 1999     

Electro-optical properties of tetragonal KNbO<Subscript>3</Subscript>

Linear electro-optical tensor coefficients and optical susceptibility of tetragonal KNbO₃ are calculated using a formalism based on bond charge theory. Results are in close agreement with the experimental data. The covalent Nb-O bonding network comprising the distorted NbO₆ octahedral groups in the structure is found to be a major contributor to the electro-optic coefficients making these groups more sensitive to these properties than the KO₁₂ groups. The orientations of the chemical bonds play an important role in determining these properties.      

OH stretching vibrations in monodomain KNbO3

Infrared absorption bands due to OH stretching vibrations have been investigated in monodomain KNbO₃ at different temperatures. The results obtained in the orthorhombic phase for polarized light suggest hydrogen positions predominantly along the O-O directions of the oxygen octahedron parallel to the spontaneous polarization.     

Electro-optical properties of nanodispersions based on ferroelectric thiobenzoates

The influence of differential nanoparticles on the properties of ferroelectric liquid crystal based on chiral thiobenzoates series was investigated by optical and electro-optical methods. MHOBS4/ZnO, MHOBS4/Ag and MHOBS10/SWCN nanocomponents were prepared. A small addition of nanoparticles leads to changes in electro-optical properties. This is due probably to the various mutual arrangements of nanoparticles and liquid crystal molecules.     

Theory of the successive phase transitions in KNbO3

The microscopic mechanism of the successive cubic-tetragonal-orthorhombic-rhombohedral phase transitions in KNbO₃ is discussed quantitatively from the microscopic free energy based upon the mean field approximation where the Nb ions are displaced to create spontaneous deformations. From the calculation of the microscopic free energy, it is shown that the order of the phase transitions and the experimental values of the transition entropy in KNbO₃ are well explained by this model.     

Electro-optical properties and photopolarization anisotropy of methacrylic azopolymer films

We have synthesized polymethacrylates with azobenzene side moieties and “spacers” of different lengths. We have studied the spectra and kinetics of the electro-optical effect appearing in films of such azopolymers after they are exposed to linearly polarized light. The nature of the electro-optical effect is explained by the appearance of photoinduced optical anisotropy in the films, due to a change in the ratio of the concentrations of trans and cis isomers of the azobenzene moieties. The characteristic time required for establishment and relaxation of photoinduced optical anisotropy correlates with the times required for a change in the dielectric characteristics of the studied films when exposed to linearly polarized light. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 76, No. 2, pp. 307–310, March–April, 2009.     

Electro-optical properties of polymer stabilized cholesteric liquid crystal film

Liquid crystals (LCs) and polymers are extensively used in various electro-optical applications.In this paper,normal mode polymer stabilized cholesteric LC film is prepared and studied.The effects of chiral dopant and monomer concentrations on the electro-optical properties,such as contrast ratio,driving voltage,hysteresis width and response time,are investigated.The reasons of electro-optical properties influenced by the concentrations of the materials are discussed.Through the proper material recipe,the electro-optical properties of polymer stabilized cholesteric LC film can be optimized.     

全息聚合物弥散液晶器件电光特性的研究

研究了全息聚合物弥散液晶(HPDLC)器件的电光特性，研究了添加不同表面活性剂对聚合物界面对液晶的锚定能的影响机理，寻求到了低工作电压的实现方法. 分析了聚合物基体与液晶折射率不匹配性对器件对比度的影响，测量了HPDLC器件的响应时间和弛豫时间，得到了平均100μs的快速响应. 关键词： 全息聚合物弥散液晶 电光特性 表面活性剂 对比度 响应时间     

KNbO3:Fe晶体的最佳二波耦合

本文在分析光折变晶体KNbO3:Fe的最佳二波耦合条件的基础上,通过计算和实验研究了晶体KNbO3:Fe的二波耦合增益系数Γ与两光束的夹角2θ、光栅矢量的取向β及不同电光系数r51或r42的关系,获得了在特定掺杂浓度N～1016cm-3条件下KNbO3:Fe晶体的最佳二波耦合条件为:θm～4°-8°并且βm～45°.     

Modelling of the phase transitions sequence in KNbO3 and BaTiO3

Interatomic potentials are determined in the framework of the nonlinear oxygen polarizability model to describe the structural behavior of KNbO₃ and BaTiO₃ as a function of temperature. To this purpose, the adiabatic potential is evaluated for different ferroelectric distortions and the model potential parameters are improved by comparing with total energies from full-potential LMTO calculations. Phonon dispersion curves are computed to test if the model reproduces the pronounced two-dimensional character instabilities found by first-principles lattice dynamics using a linear response approach. Finally, the phase diagram for KNbO₃ is obtained through a constant-pressure molecular dynamics simulation.     

Photoconductivity and light-induced absorption in KNbO3:Fe

Measurements of photoconductivity and light-induced absorption in KNbO₃: Fe are performed at different light intensities and crystal temperatures. The results are interpreted in terms of a two-center charge transport model. Different model parameters may be evaluated from the experimental data. A complete set of parameters is suggested explaining the dependences of photoconductivity and light-induced absorption on light intensity and temperature for the KNbO₃: Fe crystal investigated.