Nanoscale Ferroelectricity in Crystalline γ‐Glycine

Ferroelectrics are multifunctional materials that reversibly change their polarization under an electric field. Recently, the search for new ferroelectrics has focused on organic and bio‐organic materials, where polarization switching is used to record/retrieve information in the form of ferroelectric domains. This progress has opened a new avenue for data storage, molecular recognition, and new self‐assembly routes. Crystalline glycine is the simplest amino acid and is widely used by living organisms to build proteins. Here, it is reported for the first time that γ‐glycine, which has been known to be piezoelectric since 1954, is also a ferroelectric, as evidenced by local electromechanical measurements and by the existence of as‐grown and switchable ferroelectric domains in microcrystals grown from the solution. The experimental results are rationalized by molecular simulations that establish that the polarization vector in γ‐glycine can be switched on the nanoscale level, opening a pathway to novel classes of bioelectronic logic and memory devices.     

Conducting Domain Walls in Lithium Niobate Single Crystals

Ferroic materials play an increasingly important role in novel (nano)electronic devices. Recently, research on domain walls (DWs) receives a big boost by the discovery of DW conductivity (DWC) in BiFeO₃ and Pb(Zr_xTi_1‐x)O₃ ferroic thin films. Here, it is demonstrated that DWC is not restricted to thin films, but equally applies to millimeter‐thick wide‐bandgap, ferroic single crystals, such as LiNbO₃. In this material transport along DWs can be switched by super‐bandgap illumination and tuned by engineering the tilting angle of DWs with respect to the polar axis. The results are consistently obtained using conductive atomic force microscopy to locally map the DWC and macroscopic contacts, thereby in addition investigating the temperature dependence, DW transport activation energies, and relaxation behavior.     

BT-PMN共烧陶瓷的新的介温特性

具有不同居里点的两种铁电体粉末在共烧时会产生过渡相．这种过渡相的特性与原始物相的性质密切相关·ＢａＴｉＯ_３（简称ＢＴ）和Ｐｂ（Ｍｇ_１／３Ｎｂ_２／３）Ｏ_３（简称ＰＭＮ）共烧时,介温特性发生异常变化．结果显示,在低温端介温曲线明显抬起,表明具有更低居里温度（Ｔ_ｃ）的新相形成．而在高温端ＢＴ的^Ｔ_ｃ值升高,表明Ｐｂ进驻ＢＴ的晶格．共烧体的性能可以达到室温介电常数＞３０００,损耗＜６０,容温变化率符合Ｘ７Ｒ标准．     

67 Pb(Mg1/3Nb2/3)O3-33PbTiO3单晶90铁电畴光学研究

采用偏光显微镜观察了67Pb(Mg1/3Nb2/3)O3-33PbTiO3固溶体铁电单晶在室温时90铁电畴结构.铁电畴结构与晶体质量有关,在正交偏光显微镜下光学透明晶体中存在着尺寸为23mm的均匀大畴,不同极化方向的大畴重叠形成雾状区,使晶体表现出光学质量宏观不均匀.在光学质量差的雾状晶体中则存在着0.1mm宽的110型带状孪生畴,使晶体形成表面浮凸,带状畴内还存在着90°亚畴.并对这些畴的形成作了讨论     

The Effect of Size, Strain, and Long-Range Interactions on Ferroelectric Phase Transitions in KNbO3KTaO3KNbO3 Superlattices Studied by X-ray, EXAFS, and Dielectric Measurements

Epitaxial, uniformly strained superlattices of ferroelectric KNbO₃ and paraelectric KTaO₃ are studied with respect to their structural and dielectric properties. For dielectric measurements, perfectly lattice-matched conducting KNbO₃Sr(Ru_0.5Sn_0.5)O₃ electrodes are used, and a broad, frequency-dependent maximum is observed in the capacitance-vs-temperature curves. Niobium K-edge glancing-angle EXAFS provides information regarding the crystal structure of KNbO₃ films as thin as two unit cells in superlattices with equal KTaO₃ and KNbO₃ layer thicknesses, showing a clear difference between these thinnest-layer superlattices and films of the KNbO₃K(Ta_0.5Nb_0.5O₃ solid-solution. X-ray diffraction measurements, on the other hand, indicate that these samples exhibit the same transition temperature KNbO₃T_c, indicating the importance of long-range electrostatic interactions. Analysis of the transition temperature for various structures leads to a clear identification of the effect of size and strain on KNbO₃T_c.     

Percolative clusters in KTaO3:Li

Abstract

Percolation of polarization is considered in solid solutions of incipient ferroelectric KTaO₃: Li. The Li impurities were surrounded by a sphere of the interaction radius. The latter was thought to be proportional to the correlation radius, whichcan be represented through the dielectric susceptibility, the temperature dependence of which is well known. This temperature dependence determines the dependence of the average size of the percolative clusters on temperature. It was shown that, in the Hyper-Rayleigh scattering case, the SHG intensity is just proportional to the average size that gives an opportunity to check the idea of existing the percolative clusters by straight comparison of the experimental and theoretical result.     

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.     

烧结工艺对Sr_(0.3)Ba_(0.7)Bi_(3.7)La_(0.3)Ti_4O_(15)陶瓷显微结构及介电性能的影响

采用传统高温直接烧结和低温保温的两步烧结工艺制备铋层结构铁电陶瓷Sr0.3Ba0.7Bi3.7La0.3Ti4O15,获得结构致密、均匀、粒径介于1～3μm的陶瓷材料.结合XRD和SEM分析研究烧结工艺对陶瓷的晶相、显微结构和介电性能的影响.研究表明:采用两步烧结法使铋挥发和氧空位浓度降低,从而显著减弱了陶瓷的高温低频耗散.随着保温时间的增加,晶格畸变减少,居里温度降低了60℃左右.高温绝缘性也得到明显改善,高温电导率随保温时间的增加显著降低,保温15 h所得陶瓷样品的电导率降低了一个数量级,在280℃时为5.2×10-9S·m-1.