石墨烯和硼氮类石墨烯对LiFePO4表面结构的改进及其电导的促进作用

利用密度泛函理论研究石墨烯和硼氮类石墨烯包覆对LiFePO₄ (010)表面结构和电导性质的影响. 结果表明包覆层和LiFePO₄ (010)表面之间的相互作用可以改善LiFePO₄ (010)表面的电导性能. 石墨烯包覆LiFePO₄ (010)表面后, 禁带宽度从3.3 eV减小到2.1 eV. 硼氮类石墨烯包覆LiFePO₄ (010)表面后, 虽然其价带顶和导带底仍由Fe的3d轨道贡献, 但禁带中出现两个间隔为0.6 eV的带隙态, 由硼氮类石墨烯与LiFePO₄(010)表面有直接接触并形成共价键的B原子和N原子贡献.     

Synthesis of Novel Superhard Phases in the B-C-N System

Novel ternary diamond-like phases of the B-C-N system were synthesized at pressures up to 30 GPa and temperatures up to 3500 K by static and dynamic compression of graphite-like BN-C solid solutions. Structure and properties of these new phases were studied using X-ray diffraction with synchrotron radiation, analytical transmission electron microscopy (ATEM), electron energy loss spectroscopy (EELS), microhardness measurements and nanoindentation.     

B-C-N Compound Synthesized Under High Temperature and High Pressure

Crystalline hexagonal B(N 1 m x C x ) and cubic B-C-N compounds have been synthesized from a precursor produced from melamine and boric acid by application of high temperature and high pressure. The synthesized products were characterized by X-ray diffraction. The lattice parameters for the hexagonal crystal are a=2.506 Å, c=6.657 Å, and that for the cubic crystal is a=3.596 Å. The X-ray photoelectron spectra of the B-C-N compound indicate the presence of B-N, C-N, C-C, and B-C bonds, which suggests that boron, carbon, and nitrogen atoms all bond with one another and that the B-C-N crystal is a compound in which the three kinds of atoms are mixed atomically. The composition of the B-C-N compound is B 0.47 C 0.23 N 0.30 . A strong absorption band at 1000～1120 cm m 1 attributable to the cubic B-C-N phase is observed in the infrared spectrum. The photoluminescence spectrum of hexagonal B-C-N powder measured at room temperature features a broad peak centered at 374 nm, corresponding to the band-edge emission of h-B-C-N, and is similar to that of w-GaN.     

B0.44C0.27N0.29化合物的合成、表征和性能

以硼酸和三聚氰胺为原料，利用化学法、真空热处理及高温高压技术对BCN化合物的形成、结构及相变进行了研究．在真空10^-3Pa条件下，经1273K高温热处理得到非晶B-C-N前驱物．这种前驱物在920K以下为绝缘体，在920K由绝缘体转变为非晶半导体．在973-1003K和1013-1073K范围这种非晶半导体表现出不同的电导一温度关系，电导激活能分别为0．34eV和1．10eV，表明在两个不同的温度区域这种非晶半导体的导电机构不同．将这种前驱物在3．5GPa，经1473K退火40min后由非晶态转化为单相六方结构的B-C-N晶体，其成分为B0.44C0.27N0.29，晶格常数为a=0．2515nm，c=0．6684nm．六方B0.44C0.27N0.29晶体在1330，1364，1588和1617cm^-1出现四个强的Raman散射峰，其中1330和1617cm^-1被认为是六方B0.44C0.27N0.29晶体特征Raman散射峰.     

Formation of B-C-N Ceramics Investigated by Emanation Thermal Analysis, TG and DTA

Processes taking place during formation of B-C-N ceramics by thermal treatment of organic precursors were investigated using emanation thermal analysis (ETA), differential thermal analysis (DTA) and thermogravimetry (TG). An additional information about thermal behavior of precursors used for preparation of BC4N, BN and CNx ceramic systems by heating in argon up to 1100°C was obtained. The ETA enabled us to characterize microstructure changes in the samples at in situ conditions of thermal treatment. A good agreement of ETA, TG and DTA results was found. This revised version was published online in August 2006 with corrections to the Cover Date.     

Preparation and characterization of thick cubic boron nitride films

Cubic boron nitride （c-BN） films are prepared by the radio frequency magnetron sputtering technique. The stresses and crystallinities of the films are estimated by the Fourier transform infrared spectroscopy of c-BN samples, including the peak shifts and varieties of full widths at half maximum. The effects of the B-C-N interlayer and the two-stage deposition method on the c-BN films are investigated. Then the thick and stable c-BN films are prepared by a combination of the two methods. The properties of the interlayer and film are also characterized.     

基于非金属掺杂g-C3N4的均匀B-C-N三相单层

基于第一性原理方法计算,通过在g-C3N4中掺杂C、B和N原子,预测了四种元素均匀分布的B-C-N三元单层材料,除了B4-C3N4单层材料是一个具有1.18eV带隙的半导体,其余三种C-B-N三元单层材料都是金属材料,其中,B3C-C3N4是铁磁金金属,其净磁矩为0.57μB/原胞,可用于构建自旋电子器件材料,计算的形成能显示B-C-N三元体系具有较高的热稳定性。     

Investigations on ternary B-C-N materials

Isoelectronic BC _x N compounds have been researched widely. However, electron-deficient boron-rich B-C-N solids have also attracted much interest both theoretically and experimentally. In this paper, we introduce the synthesis, theoretical prediction, and physical properties of crystalline ternary B-C-N compounds. Our recent work reveals that the novel B-C-N materials may have a wide variety of crystal structures with different characteristics.      

新型BCN化合物的结构表征和相转变

将石墨和六方氮化硼(h-BN)混合粉球磨120h形成的非晶B-C-N粉在4.5GPa，1600K等温退火45min. XRD，TEM和Raman散射测量结果表明，高压合成的产物由晶格常数为a₁=0.2551nm，c₁=0.6716nm的六方Ⅰ相和a₂=1.2360nm，c₂=0.8570nm的六方Ⅱ相组成，其中六方Ⅱ相为B-C-N 新相. 在室温该新相在1279，1368，1398cm^-1出现三个特征Raman峰. 变温Raman测量结果表明，在测量温度T=93K时，样品中的主要相为六方Ⅰ相，随着温度的升高，六方Ⅰ相逐渐向六方Ⅱ相转变，当T>473K时，六方Ⅰ相完全转变成六方Ⅱ相. 当温度从673K降到93K过程中，样品又从六方Ⅱ相逐渐变回到六方Ⅰ相. 对这一相变的机理进行了讨论. 关键词： B-C-N 机械球磨 高温高压 相转变     

基于非金属掺杂g-C3N4的均匀B-C-N三相单层

基于第一性原理方法计算,通过在g-C₃N₄中掺杂C、B和N原子, 预测了四种元素均匀分布的B-C-N三元单层材料． 除了B₄-C₃N₄单层材料是一个具有1.18 eV带隙的半导体, 其余三种C-B-N三元单层材料都是金属材料．其中,B₃C-C₃N₄是铁磁金属,其净磁矩为0.57 μB/原胞,可用于构建自旋电子器件材料．计算的形成能显