压电材料的发展与展望

总括了压电材料的发展历程及现今的研究发展方向,简单介绍了各类压电陶瓷的特性及应用领域。详细介绍弛豫铁电单晶体、高居里温度压电陶瓷、压电复合材料,三元及多元系压电陶瓷以及无铅压电陶瓷的发展前景。     

A multiaxial lead-free two-dimensional organic-inorganic perovskite ferroelectric

Two-dimensional (2D) hybrid organic-inorganic perovskites (HOIPs) have recently gained tremendous interest because of their unique features in contrast to three-dimensional counterparts and traditional 2D materials. However, although some 2D HOIP ferroelectrics have been achieved, the issue of toxic Pb and uniaxial nature impede their further application. Herein, for the first time, we report a lead-free 2D HOIP multiaxial ferroelectric, [3,3-difluorocyclobutylammonium]₂CuCl₄ (1), which shows four ferroelectric axes and eight equivalent polarization directions, more than those of the other 2D HOIP ferroelectrics and even the inorganic perovskite ferroelectric BaTiO₃ (three ferroelectric axes and six equivalent polarization directions). 1 also features a high Curie temperature of 380 K and exhibits remarkable thermochromism of color change from green-yellow to dark brown. To our knowledge, 1 is the first multiaxial lead-free 2D HOIP ferroelectric. This work sheds light on the exploration of better lead-free 2D HOIP ferroelectrics.     

Structures and electronic properties of domain walls in BiFeO3 thin films

Domain walls (DWs) in ferroelectrics are atomically sharp and can be created, erased, and reconfigured within the same physical volume of ferroelectric matrix by external electric fields. They possess a myriad of novel properties and functionalities that are absent in the bulk of the domains, and thus could become an essential element in next-generation nanodevices based on ferroelectrics. The knowledge about the structure and properties of ferroelectric DWs not only advances the fundamental understanding of ferroelectrics, but also provides guidance for the design of ferroelectric-based devices. In this article, we provide a review of structures and properties of DWs in one of the most widely studied ferroelectric systems, BiFeO₃ thin films. We correlate their conductivity and photovoltaic properties to the atomic-scale structure and dynamic behaviors of DWs.     

Practical high-performance lead-free piezoelectrics: structural flexibility beyond utilizing multiphase coexistence

Due to growing concern for the environment and human health, searching for high-performance lead-free piezoceramics has been a hot topic of scientific and industrial research. Despite the significant progress achieved toward enhancing piezoelectricity, further efforts should be devoted to the synergistic improvement of piezoelectricity and its thermal stability. This study provides new insight into these topics. A new KNN-based lead-free ceramic material is presented, which features a large piezoelectric coefficient (d₃₃) exceeding 500 pC/N and a high Curie temperature (T_c) of  ∼200°C. The superior piezoelectric response strongly relies on the increased composition-induced structural flexibility due to lattice softening and decreased unit cell distortion. In contrast to piezoelectricity anomalies induced via polymorphic transition, this piezoelectricity enhancement is effective within a broad temperature range rather than a specific small range. In particular, a hierarchical domain architecture composed of nano-sized domains along the submicron domains was detected in this material system, which further contributes to the high piezoelectricity.     

Two-dimensional spatial manipulation of microparticles in continuous flows in acoustofluidic systems

We report a modeling and experimental study of techniques to acoustically focus particles flowing through a microfluidic channel. Our theoretical model differs from prior works in that we solve an approximate 2-D wave transmission model that accounts for wave propagation in both the solid and fluid phases. Our simulations indicate that particles can be effectively focused at driving frequencies as high as 10% off of the resonant condition. This conclusion is supported by experiments on the acoustic focusing of particles in nearly square microchannels, which are studied for different flow rates, driving frequencies and placements of the lead zirconate titanate transducer, either underneath the microchannel or underneath a parallel trough. The relative acoustic potential energy and the resultant velocity fields for particles with positive acoustic contrast coefficients are estimated in the 2-D limit. Confocal microscopy was used to observe the spatial distribution of the flowing microparticles in three dimensions. Through these studies, we show that a single driving frequency from a single piezoelectric actuator can induce the 2-D concentration of particles in a microchannel with a nearly square cross section, and we correlate these behaviors with theoretical predictions. We also show that it is possible to control the extent of focusing of the microparticles, and that it is possible to decouple the focusing of microparticles in the vertical direction from the lateral direction in rectangular channels with anisotropic cross sections. This study provides guidelines to design and operate microchip-based acoustofluidic devices for precise control over the spatial arrangement of microparticles for applications such as flow cytometry and cellular sorting.     

Behavior of positive ions in hydrogen

It has been shown that electrons with 11.5 volts energy can dissociate a hydrogen molecule into its two constituent atoms, but up until recently no experiments have been performed to see whether fast positive ions are able to dissociate hydrogen.In the present experiments Li or Cs positive ions of various velocities are produced in a tube containing hydrogen molecules. The tube is immersed in liquid air, and the rate of decrease of pressure of hydrogen is measured as a function of the velocity of the positive ions. It is found that with no positive ions entering the tube there is a certain decrease in the pressure of the hydrogen due to its thermal dissociation on the hot filament and its subsequent condensation on the cold walls of the tube. With ions of energies from 15 to 320 volts flowing in the tube the rate of decrease of pressure is greater, showing a formation of some condensible product due to the action of the ions.The rate of pressure decrease with the voltage applied has been found to be proportional to the ion current flowing. The rate per unit current is proportional to the pressure; and the rate per unit current per unit pressure is practically independent of the voltage for Li and Cs ions of energies from 15 to 320 volts.The effect has been shown not to be due to secondary electrons.The process may be due to the formation of alkali hydrides in the gas phase. The number of hydrogen molecules disappearing per positive ion entering the tube varies from 0.01 to 0.5. No critical potentials have been found in this experiment, in disagreement with recent experiments of Leipunsky and Schechter.     

非天然有机分子折叠体的组装及其对有机分子和离子的识别研究（英文）

分子折叠体是一类由非共价键稳定的、采用有序构象的寡聚物或聚合物. 我们设计并合成了三类非天然的折叠体，包括：1）由疏溶剂作用驱动的并入萘环板块的寡聚乙二醇折叠体，2）由分子内氢键驱动的寡聚酰肼折叠体，3）由分子内氢键驱动的并入锌卟啉板块的寡聚苯酰胺折叠体. 定性和定量的研究揭示，在有机溶剂中这些折叠体可以作为非天然受体分子高效络合或识别结构匹配的有机分子和离子，并且氢键驱动的折叠体可以通过络合作用实现超分子体系的手性诱导或手性放大.     

Room-temperature multiferroicity and diversified magnetoelectric couplings in 2D materials

Multiferroics are rare in nature due to the mutual exclusive origins of magnetism and ferroelectricity. The simultaneous coexistence of robust magnetism/ferroelectricity and strong magnetoelectric coupling in single multiferroics is hitherto unreported, which may also be attributed to their potential conflictions. In this paper, we show the first-principles evidence of such desired coexistence in ultrathin-layer CuCrS₂ and CuCrSe₂. The vertical ferroelectricity is neither induced by an empty d shell nor spin-driven, giving rise to an alternative possibility of resolving those intrinsic exclusions and contradictions. Compared with their bulk phases, the ferromagnetism in the thin-layer structures (two–six layers) can be greatly stabilized due to the enhanced carrier density and orbital shifting by vertical polarization, and the Curie temperatures of both ferromagnetism and ferroelectricity can be above room temperature. Moreover, a considerable net magnetization can be reversed upon ferroelectric switching, where the change in spin-resolved band structure also renders efficient ‘magnetic reading + electrical writing’. The thickness-different layers may even exhibit diversified types of magnetoelectric coupling, which both enriches the physics of multiferroics and facilitates their practical applications.     

天然氨基酸的结构和旋光性

利用螺旋理论，具体分析了天然氨基酸的构型、构象及其族光方向间的关系．结果表明，天然氨基酸遵从螺旋理论的规律．它们的旋光方向和旋光度大小都是由分子的立体结构所决定的．通过氨基酸的结构可以推断其族光方向；从旋光方向也可以推断其构型和构象。     

Winners of 2008 CAS Award for International Scientific Cooperation

On 14 January, 2009, CAS honored three foreign scientists for their lasting and fruitful contributions to the collaboration between CAS and the world： Akito Arima, president of the Japan Science Foundation, Yuen-Ron Shen, professor of physics with the University of California at Berkley, and Michel Che, catalyst expert and chair professor at Universite Pierre et Marie Curie. Their association with the Chinese scientific community can be dated back to some three decades ago.     

Properties and applications of magnetic liquids

Ferromagnetic materials such as iron, cobalt, and nickel lose their strong magnetic properties when heated to a temperature above that called the Curie temperature, a temperature which is different for different materials. For all known ferromagnetic materials this temperature is always below that of the corresponding melting points of the materials and thus intrinsic ferromagnetic liquids are not known to exist. The term magnetic liquid (or ferrofluid) as used today does not refer to an intrinsic ferromagnetic liquid but to a stable colloidal suspension of small particles of a ferromagnetic material.     

Dispersion relations for acoustic waves in heterogeneous multi-layered structures contacting with fluids

The paper describes a method and a computer application for the computation of the velocity of acoustic waves excited in complicated multi-layered structures consisting of anisotropic piezoelectric and isotropic layers. The structure assumes to be unbounded in the lateral directions. The top and bottom layers are either semi-infinite in the vertical direction or they contact with media such as fluids, gases or vacuum. A special homogenization technique enables to account for bristle-like layers contacting with a fluid. The program is supplied with a user friendly graphical interface and can be useful for researchers working on acoustic sensors.     

一种新型称重系统的理论与试验研究

目前国内外研究开发了电阻应变片式、压电式、液压式等很多不同种类的称重系统来限制超载现象。但是实际的应用表明:目前广泛应用的各种称重传感器一个共同的缺点就是容易损坏、耐久性差。本文研究了一种基于光纤Bragg光栅的新型称重系统,通过反复的试验,结果表明基于光纤光栅的称重传感器具有结构简单、实施方便、精度高、耐久可靠而且造价不高等优点,可取代传统地秤用于路桥车辆称重或长期检测,具有很好的应用前景。     

动力降尺度法对鄱阳湖区风能资源模拟效果分析

本文利用中尺度数值模式MM5以及Calmet模型,结合地面和高空观测资料对鄱阳湖区复杂地形条件下风能资源进行动力降尺度研究,并结合鄱阳湖区4个代表风场一年实测资料对模拟结果进行全面分析,得出:动力降尺度方法能够较好地模拟出鄱阳湖区风能资源的空间分布,鄱阳湖区风功率密度高值区主要在鄱阳湖区狭长湖道南侧的水域和湖岸两侧,鄱阳湖北部狭管湖道为高值中心区。风能资源的数值模拟结果月变化特征与观测期间大风出现的时间十分吻合。各风场风向、风能方向以及风速频率分布模拟与实测结果比较一致,但在量级上有一定的偏差。各风场日平均风速模拟值与实测值年相关系数为0.647～0.780,鄱阳湖区70m高度年平均风速模拟值与测风塔实测值相对误差为6.77%。总体来说,动力降尺度方法模拟效果较好,可以作为区域风能资源评价和特性分析的有效手段。     

Design and some applications of extended bandwidth finite gain amplifiers

A general theory is developed for extended bandwidth operation of actively compensated finite gain amplifiers. Designs for three new circuits are given which implement the theory. These circuits employ only operational amplifiers and resistors and their gains depend only on their resistor ratios. Thus they are suitable for IC fabrication. Further in IC technology, the characteristics of the operational amplifiers as well as the resistor ratios track closely with each other with reference to temperature and aging. Thus the extended bandwidth operation of the amplifiers will be available over a wide temperature range as well as under varying aging conditions. Their characteristics can be tuned easily by trimming only two resistors. Applications of the new amplifiers have been considered in RC active filters as well as in inductance simulation schemes. Experimental results are given which closely agree with theoretical predictions. The results also indicate that substantial improvement in the usable bandwidth of the circuits employing the new amplifiers may be expected over those using the conventional design of finite gain amplifiers.     

Optimum coherent imaging of a limited field of view in the presence of angular and aperture noise

An optimal procedure is established for the reconstruction of the angular object distribution in a given field of view (FOV). The object is coherently illuminated and located in the far zone of the receiving aperture. The procedure is “uniformly” optimal in the sense of minimizing the statistical r.m.s. difference between the object distribution, modeled as a random function of the angular coordinates and its reconstructed image, for each direction belonging to the FOV. The observable complex amplitude distribution of the field on the aperture is due in the general case not only to the incidentfield scattered by the object but also to background disturbance, or “angular noise”, randomly distributed inside and outside the FOV, and is affected by “measurement noise”, that is random errors introduced in measuring the aperture field. The reconstruction algorithm consists of summing a truncated series of special functions—prolate spheroidal for the linear case and their generalizations for two dimensional apertures—weighted by appropriate coefficients. These coefficients depend upon the observed aperture field and upon the relative power densities associated with the object field and the various types of noise. The series is truncated to a number of terms (“effective degrees of freedom” of the image) determined through an information theoretical method: each term of the series, suitably ordered, provides an information gain less than the preceding one, and the information gain goes rapidly to zero. A relationship between information transfer and mean squared error for each term in the image series is established. Numerical examples are discussed.     

Ultra-sensitive hybrid diamond nanothermometer

Nitrogen-vacancy (NV) centers in diamond are promising quantum sensors because of their long spin coherence time under ambient conditions. However, their spin resonances are relatively insensitive to non-magnetic parameters such as temperature. A magnetic-nanoparticle-nanodiamond hybrid thermometer, where the temperature change is converted to the magnetic field variation near the Curie temperature, were demonstrated to have enhanced temperature sensitivity () (Wang N, Liu G-Q and Leong W-H et al. Phys Rev X 2018; 8: 011042), but the sensitivity was limited by the large spectral broadening of ensemble spins in nanodiamonds. To overcome this limitation, here we show an improved design of a hybrid nanothermometer using a single NV center in a diamond nanopillar coupled with a single magnetic nanoparticle of copper-nickel alloy, and demonstrate a temperature sensitivity of . This hybrid design enables detection of 2 mK temperature changes with temporal resolution of 5 ms. The ultra-sensitive nanothermometer offers a new tool to investigate thermal processes in nanoscale systems.     

联苯衍生物及其类似物结构和旋光方向的关系(Ⅰ)

每种光学活性的联苯衍生物都是两种构象的混合物．在利用笔者所提出的螺旋理论［１～３］分析其旋光方向与结构间的关系时,必须确定它们的优势构象,比较取代基的可极化性大小及在优势和非优势构象中各种不同螺旋的扭曲角度（螺距的大小）．在全面考虑了这三种影响旋光性的因素条件下,可根据构型、构象推测它们的旋光方向和大小．反之,知道了它们的旋光方向和大小,也可推断它们的绝对构型和构象     

Hydrogen Breath Tests in Gastrointestinal Diseases

Hydrogen breath tests are widely used to explore pathophysiology of functional gastrointestinal (GI) disorders. Small intestinal bacterial overgrowth (SIBO) and carbohydrate malabsorption are disorders detected by these tests that have been proposed to be of great importance for symptoms of GI diseases. Glucose hydrogen breath test is more acceptable for diagnosis of SIBO whereas lactose and fructose hydrogen breath tests are used for detection of lactose and fructose maldigestion respectively. Lactulose hydrogen breath test is also used widely to measure the orocecal transit time for GI motility. These methods are noninvasive and inexpensive. Many patients with functional gut disorders are unaware of the relationship between diet and GI symptoms they present. In particular, patients with chronic symptoms may regard their condition as normal and may not be aware that their symptoms can be effectively managed following a proper diagnosis. Patients with symptoms of abdominal pain, bloating, flatulence and altered bowel movements (diarrhea and constipation), or with a medical diagnosis of irritable bowel syndrome or celiac disease, may have undiagnosed carbohydrate malabsorption or SIBO. Hydrogen breath tests are specific and sensitive diagnostic tests that can be used to either confirm or eliminate the possibility of carbohydrate malabsorption or SIBO in such patients. Breath tests, though valuable tools, are underutilized in evaluating dyspepsia and functional bloating and diarrhea as well as suspected malabsorption. However, because of their simplicity, reproducibility and safety of procedure they are now being substituted to more uncomfortable and expensive techniques that were traditionally used in gastroenterology.     

A novel technique for optimal placement of piezoelectric actuators on smart structures

The problem of positioning of actuators and sensors on smart materials has been a point of interest in recent years. This is due to the fact that in many practical applications there are limitations in space, weight, etc. of the smart structures, which make the problem of positioning more complex. In addition, it is required that the actuators/sensors have the best possible performance. The development of smart structures technology in recent years has provided numerous opportunities for vibration control applications. The use of piezoelectric ceramics or polymers has shown great promise in the development of this technology. The employment of piezoelectric material as actuators in vibration control is beneficial because these actuators only excite the elastic modes of the structures without exciting the rigid-body modes. This is important since very often only elastic motions of the structures are needed to be controlled. The purpose of this paper is to introduce a novel approach developed for optimizing the location of piezoelectric actuators for vibration suppression of flexible structures. A flexible fin with bonded piezoelectric actuators is considered in this study. The frequency response function (FRF) of the system is then recorded and maximization of the FRF peaks is considered as the objective function of the optimization algorithm to find the optimal placement of the piezoelectric actuators on the smart fin. Three multi-layer perceptron neural networks are employed to perform surface fitting to the discrete data generated by the finite element method (FEM). Invasive weed optimization (IWO), a novel numerical stochastic optimization algorithm, is then employed to maximize the weighted summation of FRF peaks. Results indicate an accurate surface fitting for the FRF peak data and an optimal placement of the piezoelectric actuators for vibration suppression is achieved.