Anomalous Magnetic Behavior in Phase-separated La0.5 Sr0.5 MnO3 +δ Films

(001)La0.5 Sr0.5MnO3 δ films on (001)LaA1O3 substrates were prepared by using a RF magnetron sputtering with powder target.At low temperature, the films exhibit two phase coexistence, which means that ferromagnetic (FM) clusters are embedded in antiferromagnetic (AFM) matrix.Moreover, a shift in hysteresis loop is unexpectedly observed in this inhomogeneous system.We suggest that the anomalous hysteresis loop may result from the unidirectional exchange anisotropy at the interface between AFM and FM clusters.     

Investigation of Structure and Hydriding Properties of La0.6 Nd0.4 Ni4.8 Mn0.2 Cux Alloys

The structure and hydriding performance of La0.6Nd0.4Ni4.8Mn0.2Cux (x = 0 ～ 0.4) alloys were investigated in order to develop suitable materials for metal hydride air conditioner. The effect of Cu addition on the crystal structure,equilibrium pressure, hydrogen capacity and hysteresis as well as hydrogen absorption/desorption kinetics were systematically studied by using the measurement of P-C isotherms, X-ray diffraction and scanning electron microscopy. As the amount of Cu increases, the plateau pressure increases and hydrogen absorption/desorption kinetics is improved, but the effective hydrogen storage capacity decreases. It is shown that variations in the basal plane parameter a can be used as an indication for the plateau pressure changes. With the increase of parameter a, the plateau pressure decreases. For La0.6 Nd0.4Ni4.8Mn0.2Cux(x = 0 ～ 0.4) alloys there is a relationship between the effective hydrogen storage capacities and the ratios of their unit cell parameters c and a. The effective hydrogen storage capacity decreases with increase of a/c.     

压电驱动晶体的特性研究

压电陶瓷迟滞特性是影响压电陶瓷驱动器位移输出精度的主要因素。在仔细研究现有的解决方案的基础上，采用Preisach模型对压电的迟滞性进行建模，并进行了相应的实验研究。实验结果证明该方法可以很好地降低压电陶瓷迟滞特性对位移输出性能的影响。而且采用压电陶瓷位移输出不回复到初始0电压状态的处理方法能够更地吻合实际情况。     

Research on seismic resistance and mechanic behavior of reinforced lightweight aggregate concrete walls after high temperature

This study focused on the mechanical behavior of reinforced lightweight aggregate concrete (RLAC) walls under repeated horizontal loads after a standard temperature‐rising fire‐resistance test and compared the specimen walls' ultimate loads, yielding loads, cracked loads, stiffness, and ductility with those of reinforced normal‐weight aggregate concrete (RNAC) walls. Steel reinforcing bar spacing, aggregate types, wall widths, and high temperatures were variables in this study. The experimental results showed that, after the fire‐resistance test, the smaller the steel reinforcing bar spacing of RLAC walls, the higher the yield and ultimate loads, yet the worse the ductility and the hysteresis loop's energy, whereas the greater the width of the wall, the greater the stiffness and the higher the hysteresis loop's energy. The differences in terms of stiffness, ductility, and hysteresis between RLAC walls with and without the fire‐resistance test were insignificant, indicating that RLAC walls do not lose their basic mechanical behavior during a high‐temperature fire. RNAC walls showed, indeed, a significant downward trend for strength and hysteresis after the fire‐resistance test, but the decrease was much less clear for stiffness. Therefore, RLAC walls did show better seismic resistance than RNAC walls under the same testing conditions. Copyright © 2013 John Wiley & Sons, Ltd.     

一种高转速水轮发电机转子动平衡的试验方法

本文对高转速水轮发电机组的动平衡试验进行了研究,提出了一种比较实用的动平衡试验方法,这种方法具有仪器设备简便,启动机组次数少,平衡精度高等优点。     

Complex structural contribution of the morphotropic phase boundary in Na0.5Bi0.5TiO3 - CaTiO3 system

The correlation between structure and dielectric properties of lead-free (1-x)Na_0.5Bi_0.5TiO₃ - xCaTiO₃ ((1-x)NBT - xCT) polycrystalline ceramics was investigated systematically by X-ray diffraction, combined with impedance spectroscopy for dielectric characterizations. The system shows high miscibility in the entire composition range. A morphotropic phase boundary (MPB), at 0.09?≤?x?<?0.15 was identified where rhombohedral and orthorhombic symmetries coexist at room temperature. The fraction of orthorhombic phase increases gradually with x in the MPB region. Dielectric measurements reveal that the relative permittivity increase with addition of Ca²⁺. This behavior is unusual with this kind of doping. A thermal hysteresis occurred only in the MPB composition which varies in a non-monotonically manner with x, detected by dielectric properties. This phenomenon is related to the crystalline microstructure by a linear relationship between the fraction of each phase and dielectric properties, and, more precisely, to the strong interaction between rhombohedral and orthorhombic phases.     

Double polarization hysteresis and dramatic influence of small compositional variations on the electrical properties in Bi4Ti3O12 ceramics

This work reports the existence of double polarization hysteresis (P–E) loop in Aurivillius-phase ferroelectric Bi₄Ti₃O₁₂ (BiT) and reveals dramatic influence of small compositional variations on the electrical properties of it. The double polarization hysteresis is a characteristic of the interaction of defects with domain walls. This characteristic becomes more pronounced in Bi-deficient and Mg-doped BiT due to an increase in oxygen vacancy concentration at the lattices. Normal and saturated P–E loop is recalled by Nb donor doping, and associated composition Bi₄Ti_2.97Nb_0.03O_12.015 (BiT-0.03Nb) shows high remnant polarization (P_r = 12.5 μC/cm²) and large field-induced strain (S₃₃ = 5.6 × 10^?4). In addition, this doping results in bulk conductivity (σ_b) of BiT decreasing dramatically and associated activity energy (E_a) increasing significantly. In contrast, high oxide ion conductivity is induced with Mg²⁺ acceptor doping, and at 600 °C the optimum composition has ionic conductivity of ?0.65 × 10^?2 S cm^?1 in the bulk.     

Scaling behavior of dynamic hysteresis of PMN-PT relaxor ferroelectric ceramics near the morphotropic phase boundary

Due to the feature of domains, ferroelectric materials display hysteresis behavior with respect to the change of the applied electric field. Every ferroelectric material has its own unique hysteresis loop reflecting the information of domain reversal under an electric field. In this work, the scaling behaviors of dynamic hysteresis in relaxor (1-x)Pb(Mg_1/3Nb_2/3)O₃-xPbTiO₃ (PMN-PT) ceramics with different compositions were studied systemically. Our results showed that the evolution of scaling behavior in PMN-PT ceramics can be divided into three stages, which is independent of the phase structure of the ceramics and the testing electric field frequency. The relationship between hysteresis area <A> and field amplitude E₀ obeys the power law <A>∝ in the low and high E₀ regions, where the reorientations of 180° and non-180° domain are dominant, respectively. However, the dynamic hysteresis area <A> does not follow the power law in the intermediate E₀ regions, which is attributed to the interaction of different domain reversal mechanisms. Furthermore, the hysteresis area <A> decreases gradually with increasing frequency at a certain E₀ and the time-dependent domain reversal process was also discussed.     

Charge storage and memory effect in graphene quantum dots – PEG600 hybrid nanocomposite

We report an easy, one step, low cost method to obtain a hybrid composite material consisting in graphene quantum dots (GQDs) embedded in a polymeric – poly(ethylene glycol) bis (carboxymethyl) ether – matrix. Optical measurements show the excitation wavelength dependent photoluminescence of the GQDs – PEG₆₀₀. In comparison with self-passivated GQDs, the composite exhibits a blue shifted photoluminescence, as well as additional emission peaks in the range of 570–600 nm. These features are explained by the presence of new electronic surface states induced by the polymeric matrix as it was demonstrated by the electrochemical measurements. The transport properties consist in a large clockwise hysteresis presenting high and low resistance states, also two distinctive regions of negative differential resistance. The photocurrent decay and the transient currents indicate a large charge storage and confirm the existence of trap charge levels. The experimental findings suggest that the leading mechanism underling the transport is Simmons Verderber. We demonstrated the switching properties of GQDs – PEG₆₀₀ for applications in non-volatile memory by performing standard sequence memory tests.     

Reversible Flat to Rippling Phase Transition in Fe Containing Layered Battery Electrode Materials

Layered sodium transition metal oxides of NaTMO₂ (TM = 3d transition metal) show unique capability to mix different compositions of Fe to the TM layer, a phenomenon that does not exist in LiTMO₂. Here, a novel spontaneous TM layer rippling in the sodium ion battery cathode materials is reported, revealed by in situ X‐ray diffraction, Cs‐corrected scanning transmission electron microscopy, and density functional theory simulation, where the softening and distortion of FeO₆ octahedra collectively drives the flat TM planes into rippled ones with inhomogeneous interlayer distance at high voltage. In such a rippling phase, charge and discharge of Na ions take different evolution pathways, resulting in an unusual hysteresis voltage loop. Importantly, upon discharge beyond a certain Na composition, the rippling TM layer will go back to flat, giving the reversibility of such structural evolution in the following cycles.