Magnetic ferroelectric materials

In the form of a succinct overview the structure and symmetry requirements of magnetic ferroelectrics are discussed. Boracites are the best-studied examples and have phases being simultaneously ferroelectric, ferromagnetic and ferroelastic. One of the salient features of such materials is the obligatory occurrence of the linear and bilinear magnetoelectric effects. They represent an invaluable auxiliary information for magnetic symmetry determination by neutron diffraction. Owing to the complexity of property combinations, work with single crystals and polarized light microscopy is obligatory. Key references of the field are given.     

Microdeformations in ferroelectrics

Ferroelectrics undergo one or more crystallographic phase transitions, which involve lattice distortions. The direction of spontaneous polarization in ferroelectrics can be reoriented by an applied electric field (or mechanical stress). There is a spontaneous strain accompanying spontaneous polarization. Phase transitions and domain reorientations thus result in microdeformations. Many devices such as actuators and transducers are based on this behaviour. The origin of microdeformations in ferroelectrics and their consequences are discussed here.     

La2O3掺杂对BST/MgO复合陶瓷显微结构和性能的影响

采用固相反应法制备了未掺杂和La2O3掺杂(0.5%、1%、2%(摩尔分数))的Ba0.55Sr0.45TiO3/MgO复合陶瓷材料,并研究了它们的显微结构和各种介电性能.研究结果表明,La2O3除一部分会进入BST晶格獭代Ba或Sr的位置外,还会有一部分与MgO等形成无定形态物质滞留在晶界,起到抑制BST晶粒生长的作用.BST/MgO复合陶瓷的居里温度随La2O3掺杂量的增大而降低,居里温度的降低导致了介电常数的减小.适量的La2O3掺杂提高了复合陶瓷的调谐性,而且La2O3掺杂明显降低了复合陶瓷的微波介电损耗.0.5%(摩尔分数)La2O3掺杂的BST/MgO复合陶瓷具有最佳的综合介电性能,其在10kHz下的调谐性为6.9%(2kV/mm),3.99GHz时的介电常数和介电损耗分别为87.5和3.35×10-3,基本可以满足铁电移相器的使用要求.     

Optical-induced absorption tunability of Barium Strontium Titanate film

The absorption tunability of 100 nm thickness of ferroelectric Barium Strontium Titanate (Ba_0.5Sr_0.5TiO₃) thin films with different densities of pumped optical field is measured by terahertz time-domain spectroscopy in the range of 0.2 THz – 1.2 THz at 19 °C. Experimental results show that the absorption coefficient of BST film is approximately at 5000 cm⁻¹–20000 cm⁻¹ in the range of 0.2 THz – 1.2 THz and the absorption coefficient reached up to 16% when we applied the optical field up to 600 mW. The theoretical calculations reveal that increasing photoexcitation fluences is responsible for the increasing of transmission change in the conduction current density cause the absorption coefficient varied.     

考虑内陆转运的集装箱班轮运输网络设计方法

为了优化班轮公司航线网络,降低运营成本,针对始发地或目的地位于内陆,且内陆与港口间存在转运OD流的班轮航线进行网络设计。基于Logit和整数线性规划等方法,将内陆OD流转化为港到港需求,建立集装箱班轮航运网络评估模型。模型以总成本最小为目标,同时满足货运需求、装卸港转运时间以及合理安排运力等约束,利用IOLG CPLEX优化软件进行求解。将模型用于某班轮公司航线网络设计,与现有结构相比优化结果显示：在保持总运量大致持平的基础上,可将原有船队规模从81条航线、289只船舶有效缩减到77条航线和269只船舶。表明该模型能够有效降低班轮航线运营成本,具有较大的实践意义。     

铌酸钠钾基压电陶瓷的电场诱导介电特性

采用传统的固相反应合成法制备了0.9(K0.5Na0.5)NbO3-0.1LiSbO3(KNN-LS)无铅压电陶瓷,研究了它在不同直流偏置电场下的介电常数的频谱,并分析了直流偏置电场诱导下的相对介电常数变化值Δrε和调谐率K.随着偏置电场的增大,Δrε和K都变大,这与传统的钛酸锶钡陶瓷类的材料结果相反.同时,随着频率的增加,Δrε和K都减小.Δrε随偏置电压的增加而增大,意味着在高的电压下,样品的色散效应增大,其原因可以用空间电荷的极化理论来解释.另外,在外加偏置电压不高的情况下(3 kV/cm),就可以获得相对较大的调谐率1.17%.     

Some current problems in perovskite nano-ferroelectrics and multiferroics: kinetically-limited systems of finite lateral size

Abstract

We describe some unsolved problems of current interest; these involve quantum critical points in ferroelectrics and problems which are not amenable to the usual density functional theory, nor to classical Landau free energy approaches (they are kinetically limited), nor even to the Landau–Kittel relationship for domain size (they do not satisfy the assumption of infinite lateral diameter) because they are dominated by finite aperiodic boundary conditions.     

Some current problems in perovskite nano-ferroelectrics and multiferroics: kinetically-limited systems of finite lateral size

We describe some unsolved problems of current interest; these involve quantum critical points in ferroelectrics and problems which are not amenable to the usual density functional theory, nor to classical Landau free energy approaches (they are kinetically limited), nor even to the Landau–Kittel relationship for domain size (they do not satisfy the assumption of infinite lateral diameter) because they are dominated by finite aperiodic boundary conditions.     

A designer approach to plasmonic nanostructures: tuning their resonance from visible to near-infrared

Using Green's matrix method and resonance capacity concept, surface plasmon resonances of metallic nanostrips are investigated. We first show how the resonance wavelength is determined by the geometric parameters. Then, resonances from visible to near-infrared, depending on the strip size, are obtained. For a specific nanostrip-type, a linear tunability of resonance wavelength is demonstrated from λ_R = 900 nm to λ_R = 1800 nm by merely changing the dimensions and keeping the aspect ratio fixed. It is also found that the near field is more enhanced around the thin and long nanostrip. These results can act as a guide in practical design work.     

含稀土配合物的聚丙烯酸酯的荧光可调控性能研究

用化学络合的方法制得含弱荧光稀土离子镨Pr(Ⅲ)和铒Er(Ⅲ)的单体,并经自由基聚合方法制得含Pr(Ⅲ)和Er(Ⅲ)的聚丙烯酸酯聚合物.通过对聚合物薄膜的荧光分析发现,敏化离子La(Ⅲ)、Y(Ⅲ)、Yb(Ⅲ)的引入,使含弱荧光稀土离子镨Pr(Ⅲ)和铒Er(Ⅲ)的聚丙烯酸酯表现出了明显的荧光发射特性,且通过引入这些敏化离子,可实现对上述聚合物的特征荧光发射光谱的调控作用;同时发现敏化离子Yb(Ⅲ)对上述两种聚合物的荧光调控作用都较为明显.     

Sol-Gel制备Ba1-x Srx TiO3系铁电薄膜的介电、调谐性能*

用sol-gel工艺制备Ba1-xSrxTiO3系铁电薄膜（1－x=0.3,0.5-0.9)。实验证实,在制备溶胶过程中,提高加热温度能有效增加BST薄膜的介电调谐百分率。室温下,100kHz,各组分薄膜的介电常数（ε）和介电调谐百分率（Tunability%)均呈现较高的值。其中,Ba0.8Sr0.2TiO3的介电常数和调谐百分率达到最大分别为：678和39％,比国际上同类文献报道的数据高。BST的ε－E曲线呈良好的单值函数关系。介电温谱出现明显宽化,调谐曲线峰值点对应的温度较居里温度低20－30℃,本文并对上述现象作出解释。     

Polarisation behaviour of diode lasers with frequency selective feedback

The paper reviews recent results obtained with diode lasers used in external hybrid cavities with frequency selective feedback. Such cavities attract continuing interest for several reasons. They generate a tunable single laser mode with very low linewidths (usually a few tens of kilohertz). Very wide discrete tunable ranges over 100 nm for Fabry-Perot type and over 200 nm for quantum well lasers are achieved. They can be made to oscillate in a tunable mode having the desired polarization state,TE orTM and, in some cases, simultaneously atTE andTM. This is done by designing a cavity that increases strongly theTM/TE intensity ratio and by using coatings on one laser facet that greatly lower bothTE andTM reflectivities. High-speed polarization switching in the gigahertz range is possible by inserting passive or active polarization selecting elements in the cavity. For all these reasons hybrid external cavities are attractive for applications in optical metrology, spectroscopy and optical communications. Moreover, the external cavity configuration allows the study of physical mechanisms in the laser diode by inducing on purpose phenomena that would have been otherwise impossible to achieve with free-running lasers.     

基于ARM的嵌入式系统中FPGA配置方式研究

介绍了基于SRAM LUT结构的FPGA的几种在线配置方式,同时给出了在嵌入式系统中利用ARM7TDMI微处理器产生FPGA配置时序的方法;给出了最小系统应用电路;结合程序,分析如何产生FPGA的配置时序;本方案的实用性在本文得到充分说明.