BaTiO_3晶体中的负晶结构和对电畴结构的影响

本文从结晶化学角度出发，结合晶体的生长工艺研究了顶部籽晶溶盐法（ＴＳＳＧ）生长ＢａＴｉＯ３晶体中的包裹体形成机理及其对电畴结构的影响。在ｃ轴籽晶生长的晶体中，包裹体主要是沿着籽晶分布在晶体的放肩起始区域里。通过显微观察发现，通常为四方锥形和四方台形两种几何形状，并以四方锥形为多见。四方锥形的锥顶方向与提拉方向相反，指向溶液；锥面与｛１１１｝面族平行，晶体中四方锥形包裹体的结晶形貌和方位完全相同，具有负晶结构的特性。四方台形包裹是未发育完整的四方锥包裹体。通过定向发现，ＢａＴｉＯ３晶体中负晶的四个锥面与晶体中｛１１１｝面族的四个锥面平行是一种内向生长机理。结合晶体生长的物理化学条件，从包裹体的分布和结晶方位来分析，提出该种负晶体结构包裹体的形成是由于在放肩阶段，肩部面积按指数律增加，热量容易耗散；与此同时，因晶体转动的线速度是由缘及里逐渐减慢，位于籽晶下方的晶体与溶液之间的相对流动减少，导致径向温度梯度由边缘向中央逐渐降低。在ＢａＴｉＯ３晶体放肩生长时容易形成凹的固液界面，易将溶液包裹在晶体的中部。根据负离子配位多面体生长基元的理论模型，被包裹的溶液在冷却过程中是以ＴｉＯ６八面体和Ｂａ２＋（或ＢａＯ１２立方八?

三硼酸锂晶体中负晶的观察

采用光学显微镜、X射线形貌术以及激光散射层析等方法,对新型非线性光学材料三硼酸锂晶体中的一种特殊的包裹体——负晶进行观测和研究,揭示了它的本质和组成,探讨了它的形成机理。

光电负阻晶体管PNEGIT的电路模型和模拟

给出了光表面控制负阻晶体管 PNEGIT( Photo- Controlled Surface Negative ImpedanceTransistor)的电路模型 ,从栅控晶体管数学模型出发并结合光电池的电路模型 ,用电路模型描写带有表面复合和体复合的器件 ,模型为研究 PNEGIT和表面控制负阻晶体管 NEGIT( Surface- Controlled Negative Impedance Transistor)以及探讨该类器件的新用途提供了一种手段 。

6H-SiC单晶的生长与缺陷

采用升华法 ,在一定的温度、气体压力和流量的条件下 ,生长了尺寸 5 0 .8mm的 6HSiC单晶。利用光学显微术观察了原生晶体的表面形貌 ,发现了微管在晶体表面的露头点具有明显的多个螺位错成核特征。采用透射模式对抛光晶片进行观察 ,发现了SiC晶体内的典型缺陷 ,如 :负晶、微管、碳颗粒等 ,并对它们的形成机理进行了讨论。

草莓红绿柱石(Pezzottaite)的晶体结构测定及其意义

利用CCD单晶衍射仪对草莓红绿柱石进行晶体结构测定,测定其空间群为R3c,并讨论了结构中Li+有序地置换Be2+造成c/a值的变化特征。晶体中发现复三方偏三角面体的负晶包裹体,其宏观对称属m,它与空间群Rc相对应,但与测出晶体结构的空间群有矛盾。X射线结构测定已否定了其空间群为Rm的看法。要解决草莓红绿柱石晶体空间群是否有对称中心(Rc或Rc)的问题,还需进一步将X射线结构的数据及其有关的电性实验结合分析。

尖晶石的八面体包裹体成分及成因探究

目前对于尖晶石内部八面体包裹体的成分,宝石学研究中尚存在争议。基于市场上尖晶石主要产地为缅甸且八面体包裹体为缅甸及斯里兰卡产地的特征包裹体的两方面考虑,对收集到的52粒主要产地为缅甸的尖晶石样品进行观察,据包裹体存在的共性及包裹体所处位置选择较有代表性的4颗宝石级尖晶石样品进行显微观察和拉曼光谱测试。拉曼光谱显示包裹体有位于155、282、712、1 086cm-1的方解石拉曼峰和位于177、300、1 099cm-1的白云石拉曼峰。通过对八面体包裹体分布特征的观察,从突起、空间分布、偏光特点和成分等方面分析,得出结论:缅甸尖晶石内部的包裹体若呈白色或无色、边界清晰、定向排列、八面体形状,则可以判断他们是由残余成矿热液白云石或方解石所充填的同生、次生或假次生负晶包裹体。但由于研究样品数量和来源的局限性,对于其他尖晶石族矿物作为八面体包裹体的存在缺乏相关证据,有待进一步验证。

Designing Conformal Electrode-electrolyte Interface by Semi-solid NaK Anode for Sodium Metal Batteries

Solid-state Na metal batteries(SSNBs),known for its low cost,high safety,and high energy density,hold a significant position in the next generation of rechargeable batteries.However,the urgent challenge of poor interfacial contact in solid-state electrolytes has hindered the commercialization of SSNBs.Driven by the concept of intimate electrode-electrolyte interface design,this study employs a combination of NaK alloy and carbon nanotubes to prepare a semi-solid NaK(NKC)anode.Unlike traditional Na anodes,the paintable paste-like NKC anode exhibits superior adhesion and interface compatibility with both current collectors and gel electrolytes,significantly enhancing the intimate contact of electrode-electrolyte interface.Additionally,the filling of SiO_(2)nanoparticles improves the wettability of NaK alloy on gel polymer electrolytes,further achieving a conformal interface contact.Consequently,the overpotential of the NKC symmetric cell is markedly lower than that of the Na symmetric cell when subjected to a long cycle of 300 h.The full cell coupled with Na_(3)V_(3)(PO_(4))_(2)cathodes had an initial discharge capacity of 106.8 mAh·g^(-1)with a capacity retention of 89.61%after 300 cycles,and a high discharge capacity of 88.1 mAh·g^(-1)even at a high rate of 10 C.The outstanding electrochemical performance highlights the promising application potential of the NKC electrode.

Stable and reversible zinc metal anode with fluorinated graphite nanosheets surface coating

A highly stable zinc metal anode modified with a fluorinated graphite nanosheets(FGNSs)coating was designed.The porous structure of the coating layer effectively hinders lateral mass transfer of Zn ions and suppresses dendrite growth.Moreover,the high electronegativity exhibited by fluorine atoms creates an almost superhydrophobic solid-liquid interface,thereby reducing the interaction between solvent water and the zinc substrate.Consequently,this leads to a significant inhibition of hydrogen evolution corrosion and other side reactions.The modified anode demonstrates exceptional cycling stability,as symmetric cells exhibit sustained cycling for over 1400 h at a current density of 5 mA/cm^(2).Moreover,the full cells with NH_(4)V_(4)O_(10)cathode exhibit an impressive capacity retention rate of 92.2%after undergoing 1000 cycles.

Effects of crystallinity, {001}/{101} ratio, and Au decoration on the photocatalytic activity of anatase TiO_2 crystals

Anatase TiO2 nanocrystals and sub-microcrystals with truncated octahedral bipyramidal morphologies were prepared by direct calcination of TiOF2 precursors. The as-prepared TiO2 samples were thoroughly characterized by X-ray diffraction, Raman spectroscopy, field-emission scanning electron microscopy, N2 adsorption-desorption isotherms, X-ray photoelectron spectroscopy, and UV-visible diffuse spectroscopy. It was found that the crystallinity, grain size, and {001}/{101} ratio of the samples can be increased by raising the calcination temperature from 500 to 800℃. The higher crystallinity and {001}/{101} facet ratio resulted in an increase in both aqueous and gas-phase photocatalytic activities, by inhibiting the recombination and separation of electrons and holes. After selecting two TiO2 samples with high crystallinity and {001}/{101} ratio, Au nanoparticles were decorated on their surfaces, and the photocatalytic activity of the resulting samples under visible light illumination was studied. It was found that the visible light-induced photocatalytic activity increased by 2.6 and 4.8 times, respectively, upon Au decoration of the samples prepared by calcination of TiOF2 at 700 and 800℃.

Modeling and Simulation of Photoelectronic Lambda Bipolar Transistor

Based on the region model of lambda bipolar transistor ( LBT), a dividing region theory model of PLBT is set up,simulated and verified. Firstly, the principal operations of different kinds of photoelectronic lambda bipolar transistor ( PLBT) are characterized by a simple circuit model. Through mathematical analysis of the equivalent circuit, the typical characteristics curve is divided into positive resistance, peak, negative resistance and cutoff regions. Secondly, by analyzing and simulating this model, the ratio of MOSFET width to channel length, threshold voltage and common emitter gain are discovered as the main structure parameters that determine the characteristic curves of PLBT. And peak region width, peak current value, negative resistance value and valley voltage value of PLBT can be changed conveniently according to the actual demands by modifying these parameters. Finally comparisons of the characteristics of the fabricated devices and the simu- lation results are made, which show that the analytical results are in agreement with the observed devices characteristics.

Effects of negative index medium defect layers on the transmission properties of one-dimensional photonic crystal

The photonic band gap structure of 1D photonic crystal with a negative index medium defect layer is studied by using the transfer matrix method. Investigations show that the introdufion of negative index medium defect layer and the increase of the negative index value will result in an extension of the band gap. Moreover, by increasing the negative index, the width of defect layer and the numbers of period photonic crystal, the width of defect modes will be narrowed, which is advantaged to obtain optical filters with narrow band. Finally, the effects of absorption on the properties of band gap and on defect modes have been discussed.

Design and Fabrication of Novel Dual-Base Negative-Differential-Resistance Heterojunction Bipolar Transistor

Based on planar Si dual-base transistor conception, a novel mesa dual-base heterojunc- tion bipolar transistor ( HBT) is designed and fabricated. Molecule beam extension. selective wet chemical etching, common contact photolithography and metal lift-off technique are adopted in the process. The device has particular and distinct voltage-controlled negative differential resistance (NDR) and photo-controlled NDR. The highest peak-to-vally current rate of the voltage-controlled NDR is larger than 148 and the peak current varies with the increase of collector voltage. The device features high speed and high frequency characteristics derived from HBT and intrinsic bistability and self-latching characteristics due to NDR. A single dual-base HBT can be seen as an integration of NDR device, HBT and photoconductive device. Compared with common HBT.the groove is the key factor producing NDR.

Hydrothermal Synthesis and Electrochemical Properties of Amorphous LiMoS2 as a High Capacity Anode Material for Lithium Ion Batteries

The LiMoS： anode material for lithium ion rechargeable batteries were synthesized by a hydrothermal method at 150 ℃. According to our measurements with X-ray diffraction, LiMoS2 was amorphous structure. Electrochemical measurements results showed that LiMoS2 exhibited large lithium storage capacities.

Mesocrystal Co3O4 nanoplatelets as high capacity anode materials for Li-ion batteries

Faceted crystals with exposed highly reactive planes have attracted intensive investigations for applications. Herein, we demonstrate a general synthetic method to prepare mesocrystal Co3O4 with predominantly exposed {111} reactive facets by the in situ thermal decomposition from Co（OH）2 nanoplatelets. The mesocrystal feature was identified by field emission scanning electron microscopy, transmission electron microscopy, selected area electron diffraction, and N2 isotherm analyses. When applied as anode material in lithium-ion batteries, mesocrystal Co3O4 nanoplatelets delivered a high specific capacity and an outstanding high rate performance. The superior electrochemical performance should be ascribed to the predominantly exposed {111} active facets and highly accessible surfaces. This synthetic strategy could be extended to prepare other mesocrystal functional nanomaterials.

Multi-dimensional wave steering with higher-order topological phononic crystal

The recent discovery and realizations of higher-order topological insulators enrich the fundamental studies on topological phases.Here,we report three-dimensional(3D)wave-steering capabilities enabled by topological boundary states at three different orders in a 3D phononic crystal with nontrivial bulk topology originated from the synergy of mirror symmetry of the unit cell and a non-symmorphic glide symmetry of the lattice.The multitude of topological states brings diverse possibilities of wave manipulations.Through judicious engineering of the boundary modes,we experimentally demonstrate two functionalities at different dimensions:2D negative refraction of sound wave enabled by a firstorder topological surface state with negative dispersion,and a 3D acoustic interferometer leveraging on second-order topological hinge states.Our work showcases that topological modes at different orders promise diverse wave steering applications across different dimensions.

The growth mechanism of the basic magnesium chloride whisker

Based on the theoretical model of anion coordination polyhedron growth units, the growth mechanism of the basic magnesium chloride whisker was discussed in this paper.It was found that the basic magnesium chloride whisker habits were related to the different environments in which anion coordination polyhedra grew. The growth units of basic magnesium chloride whiskers are [Mg - (OH) 4]2 -and [Mg - Cl 4]2 -. The growth process is the incorporation process of growth units. Growth units will have different incorporations and orientations caused by different system characters or heating. Furthermore, the formation mechanism of basic magnesium chloride whiskers was also interpreted using anion coordination polyhedron growth units.