钛酸锶钡的铁电相变与晶胞体积的关联

考察了Ba_μSr_1-μTiO₃(BST)的T_C对晶格 参数γ的依赖关系.并对BST的依赖关系与BaTiO₃和SrTiO₃的相应依 赖关系进行了比较.得到了一个观点：BST的T_C的变化可归因于晶胞体积效应.还 从体积效应的观点对BST相变的弥散性和级进行了讨论.BST的晶胞体积效应可归因于BST中Ba 和Sr的离子化现象. 关键词： 铁电性 钛酸锶钡 晶胞体积效应     

钛酸铋钡陶瓷的介电性、铁电性及对晶格结构的依赖性

采用溶胶-凝胶工艺成功制备出BaBi₄Ti₄O₁₅微细粉料，并利用此微粉烧结出成瓷良好的BaBi₄Ti₄O₁₅陶瓷.研究了BaBi₄Ti₄O₁₅陶瓷的铁电 顺电相 变，测定了BaBi₄Ti₄O₁₅的介 电特性和饱和状态下的铁电特性.所作测量表明B 关键词： 铁电性 介电性 晶格结构 溶胶 凝胶法     

磁致多铁性物理与新材料设计

磁致多铁材料是多铁性材料大家族中的后起之秀,其特色在于其铁电性起源于特定的磁序,因此其铁电性与磁性紧密关联,具有本征的强磁电耦合效应。目前对磁致多铁性的研究以基础物理为主。随着对磁致多铁现象背后物理机制认识的不断深入,不断有新的磁致多铁材料被设计、预言和发现,其性能也在不断地提高。文章简要介绍了磁致多铁材料所涉及的基本物理机制,并根据这些已知的规律,回顾了近年来寻找和设计新的磁致多铁材料的经验。     

光子诱导多铁性薄膜非接触式信息读取新方法

作为一种显著的多铁性材料,由于BiFe0₃的禁带宽度位于可见光波段,近年来它独特的光学性质(例如,可翻转的光伏效应、不同于传统材料的大于禁带宽度的光生电压、光致伸缩效应等)格外引人关注。作者将一束能量大于材料禁带宽度的激光引入原子力显微镜中,利用开尔文力显微技术,测量到不同电畴结构的表面电势差长时间衰减后的光致恢复效应。这种光致电势恢复可以理解为被拉到表面的光生载流子导致的表面电荷重新分布的结果。这一结果展现了一种新的铁电性材料的光学特性,并提供了一种把光学性质应用于非破坏性读取铁电存储信号的新思路。     

Numerical Study of Switching Behavior in Finite Media Subject to 3D Ferroelectric-Paraelectric Interactions and Inspection of Calibration Effects

We study numerically the switching behavior aspects and calibration effects relative to finite media embedding fully a three-dimensional ferroelectric layer in a paraelectric environment. Our approach makes use of the Ginzburg-Landau formalism in combination with the electrostatics equations. The associated discrete nonlinear system, which arises from finite element approximations, is solved by an inexact Newton method. The resulting numerical experiments highlight the effects of a balance between the physical and geometrical parameters. In particular, the same state switchings can be retrieved from different ferroelectric layer sizes by acting upon the physical characteristic of the paraelectric environment. Ferroelectric platelet samples are in parallelepipedic and cylindrical configurations involved in these experiments.     

Liquid phase demixing in ferroelectric/semiconducting polymer blends: An experimental and theoretical study

This article describes a combined experimental and theoretical study on nanophase structure development as a result of liquid phase demixing in solution‐cast blends of the organic semiconductor poly(9,9′‐dioctyl fluorene) (PFO) and the ferroelectric polymer poly(vinylidene fluoride‐co‐trifluoroethylene) (P(VDF‐TrFE)). Blend layers (200 nm) are prepared by spin coating a 1:9 (w/w) PFO:P(VDF‐TrFE) blend solution in a common solvent on a poly(ethylenedioxy thiophene)/poly(styrene sulfonate) substrate. Owing to the pronounced incompatibility between the two polymers, a strong phase‐separated morphology is obtained, characterized by disk‐like nanodomains of PFO embedded in a P(VDF‐TrFE) matrix, as revealed by scanning electron microscopy. By varying the processing conditions, we find the average domain size and standard deviation to increase with spinning time. The considerable increase in domain size suggests the coarsening process not to be impeded by a steep rise in viscosity. This indicates solvent evaporation to be only moderate within the experimental time frame. The evolution of the observed phase morphology is modeled using ternary diffuse interface theory integrated with a modified Flory–Huggins (FH) treatment of the homogeneous (bulk) free energy of mixing, to account for significant molecular differences between the active blend components. Using calculated FH interaction parameters, the model confirms the phase separation to occur via spinodal decomposition of the blend solution during spin coating, as suggested by experimental observations. The simulated phase morphologies as well as the modeled trends in domain growth and standard deviation compare favorably with the experimental data. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 49: 1255–1262, 2011     

The doping effects of BiFe1-xCoxO3 (x=0.0-0.8) in layered perovskite Bi4Ti3O12 ceramics

Bi5Fe1-xCoxTi3O15(x = 0.0, 0.2, 0.4, 0.5, 0.6, and 0.8) multiferroic ceramics are synthesized in two steps using the solid state reaction technique. X-ray diffraction patterns show that the samples have four-layer Aurivillius phases. At room temperature (RT), the samples each present a remarkable coexistence of ferromagnetism (FM) and ferroelectricity (FE). The remnant polarization (2P r ) reaches its greatest value of 14 μC/cm 2 at x = 0.6. Remnant magnetization (2M r ) first increases and then decreases, and the greatest 2M r is 7.8 menu/g when x = 0.5. The magnetic properties for x = 0.4 are similar to those for x = 0.6, indicating that the magnetic properties originate mainly from the coupling between Fe 3+ and Co 3+ ions, rather than from their own magnetic moments.     

Ferroelectric and optical properties of ‘Ba-doped’ new double perovskites

Solid solution of Pb_1.5Ba_0.5BiNbO₆ ceramic is explored here to obtain its ferroelectric and optical properties. The polycrystalline sample was prepared by a standard solid state reaction route. Room temperature XRD and FTIR spectra of the compound exhibit an appreciable change in its crystal structure of Pb₂BiNbO₆ on addition of ‘Ba’ in A site. The surface morphology of the gold-plated sintered pellet sample recorded by SEM exhibits a uniform distribution of small grains with well-defined grain boundaries. Detailed studies on the nature of polarization and variation of dielectric constant, tangent loss with temperature as well as frequency indicate the existence of Ferro-electricity in the sample. Using UV-Vis spectroscopy, the optical band gap of the studied sample has been estimated as 2.1 eV, which is useful for photo catalytic devices. Photoluminescence analysis of the powder sample shows a strong red photoluminescence with blue excitation, which is basically useful for LED.     

Doping of polyvinylidene difluoride with cobalt nitrate: Structural,electrical, and magnetic properties

Polyvinylidene difluoride (PVDF) doped with a few percentage of cobalt nitrate hexahydrate induces transition into the ferroelectric β‐phase. Infrared spectra show peaks indicative of β‐phase PVDF at 1277 cm^?1 and loss of the α‐phase peak at 790 cm^?1 while polarization measurements show loops consistent with relaxor ferroelectric behavior. Electronic spectroscopy shows that the Co²⁺ ion is in a six‐coordinate environment, and this is confirmed by magnetic susceptibility. Thermal measurements show that the PVDF melts near 155 °C, depending on the Co²⁺ content, and that there are several other thermal features that are associated with the hydrated cobalt nitrate. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012