共查询到19条相似文献,搜索用时 156 毫秒
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基于密度泛函理论的赝势-平面波方法,采用三种模型分别研究Li,N原子对N—H键方位的影响以及N—H键间的相互影响,得到了Li2NH的晶体结构和H原子的占位位置.计算结果表明:Li2NH晶体为层状结构,空间群为P42,晶胞中4个N—H键分为两层,层内N—H键为反平行排列,层间N—H键为垂直排列.态密度和电子局域函数(ELF)分析表明,N—H键呈明显的共价键特性,Li和N—H键呈明显的离子键相互作用.可逆储氢反应Li2NH+H2/LiNH2+LiH在温度0K时的反应焓为69.6kJ/molH2,与实验结果66kJ/molH2符合得较好. 相似文献
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用Mg和Mg3N2作触媒,以LiH作添加剂,在55—64千巴及1700—2100℃的高温高压下,进行了由六方氮化硼到立方氮化硼的合成。对合成晶体作了结构与有关性能的鉴定和测试。晶体表面上杂质、缺陷、生长中心和台阶结构的显微观察表明,高温高压下合成的立方氮化硼晶体具有通常条件下晶体生长的一般特征。对密切依赖于温度、压力状况及触媒组装的合成结果进行了分析和讨论。文中特别报道了触媒中少量LiH的加入对提高晶体粒度和质量的显著效果,其中获得了1毫米以上的大颗粒立方氮化硼晶体。 相似文献
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采用第一性原理方法研究了NH3分子在LiH(100)晶面的表面吸附情况. 通过研究LiH(100) /NH3体系的吸附位置、吸附能和电子结构,发现NH3分子在Li3N (100)晶面主要是化学吸附,初始位置为NH3分子中N-H键在Li顶位时失去一个H原子,并在LiH(110)面形成NH2基,其吸附能为0.511 eV,属于强化学吸附,吸附作用最强. 此时NH2基与附近H原子和Li原子之间为离子键作用,NH2基中N—H键为共价键;NH3分子中另一个H原子与LiH表面的一个H原子形成一个H2分子逸出表面. H2分子中H-H键为明显的共价键. 相似文献
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引入调节剂是一种改善立方氮化硼生长环境的重要手段. 本文中,我们研究了在Li3NhBN体系中引入调节剂对合成立方氮化硼的影响. 研究发现,调节剂的引入对立方氮化硼成核有明显的影响,并且通过光学显微镜可以明显发现调节剂曾有溶融的迹象,认为是调节剂在高温高压下发生溶解,改变了立方氮化硼生长溶液的性质,为立方氮化硼的生长提供了良好的生长环境,改变了立方氮化硼的生长速度,使晶体形貌得到了明显的改善. 通过电镜分析,发现调节剂含量的不同给晶体带来了不同的缺陷. 相似文献
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研究了常压高温下Li3N在B4 C与含氮化合物生成BN反应中的作用。实验结果表明 ,在 950℃高温下 ,B4 C与Si3N4 反应不生成hBN ,B4 C与NH4 Cl反应只生成少量hBN。在该两种原料中加入Li3N后 ,反应产物中hBN的生成量都明显增多。但Li3N本身没有与B4 C生成hBN的反应。由此推断 ,Li3N在上述B4 C与含氮化合物生成hBN的反应中表现出了催化作用。此外 ,在以hBN为原料 ,以Li3N为催化剂合成出cBN的温度压力区域内 ,对B4 C Si3N4 Li3N体系所做的高温高压实验没有合成出hBN或cBN。还讨论了在低压条件下原位合成cBN的探索实验中 ,应如何选择硼源和氮源的问题 相似文献
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The structural characteristics and chemical, morphological, and optical properties of cBN and cBN:Gd micropowders are studied by x-ray diffraction, energy-dispersive electron probe microanalysis (x-ray spectral microanalysis), and photoluminescence techniques. Cubic boron nitride (cBN) micropowders were synthesized at high pressures and temperatures from hexagonal boron nitride (hBN) micropowder and Li3N catalyst. cBN:Gd micropowders were synthesized from mixtures of hBN, Li3N, and GdF3 micropowders. A lattice parameter of a~3.615 ? is calculated for both types of powder (cBN and cBN:Gd). The photoluminescence spectra of the cBN:Gd powder are found to contain emission lines attributable to intracenter optical transitions of Gd3+ ions. 相似文献
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以(C2H5)2O·BF3和Li3N为原料,于苯热条件下合成氮化硼并研究其相变机理。X射线粉末衍射和傅立叶变换红外吸收光谱分析证明,产物中不仅有hBN和cBN物相存在,而且还发现了正交氮化硼(oBN)和锂硼氮的常压相Li3BN2(O)及高压相Li3BN2(T)存在。分析了Li3BN2在高温高压条件下和在苯热条件下对合成cBN催化机制的差异,探讨了Li3BN2在以Li3N和(C2H5)2O·BF3为原料合成BN的催化机制,提出常压相Li3BN2(O)和高压相Li3BN2(T)分别对生成cBN和oBN起催化作用的观点。 相似文献
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A chemical reaction for the preparation of B-C-N compounds by using carbon tetrachloride (CC14), boron tribromide (BBr3), lithium nitride (Li3N) and sodium as reactants has been carried out at the temperature of 400℃. Measurements of FTIR, XRD, TEM and EELS show that two kinds of compounds have been formed in the prepared sample. One is hollow sphere-like C-N with an amorphous, structure; the other is piece-like polycrystalline B-C-N with the hexagonal structure. Their determined compositions are close to C3N and BC2N, respectively. 相似文献
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Hetero-Epitaxial Diamond Single Crystal Growth on Surface of cBN Single Crystals at High Pressure and High Temperature 下载免费PDF全文
We report a new diamond synthesis process in which cubic boron nitride single crystals are used as seeds, FesoNi20 alloy powder is used as catalyst/solvent and natural flake-like graphite is used as the carbon source. The samples are investigated using laser Raman spectra and x-ray diffraction (XRD). Morphology of the sample is observed by a scanning electron microscope (SEM). Based on the measurement results, we conclude that diamond single crystals have grown on the cBN crystal seeds under the conditions of high temperature 1230℃ and high pressure 4.8 GPa. This work provides an original method for synthesis of high quality hereto-semiconductor with cBN and diamond single crystals, and paves the way for future development. 相似文献
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Shigehito Isobe Haiyan Leng Hironobu Fujii Yoshitsugu Kojima 《Journal of Physics and Chemistry of Solids》2008,69(9):2234-2236
Li-Mg-N-H systems composed of Mg(NH2)2 and LiH with various ratios can reversibly store a large amount of hydrogen under the temperature condition above 150 °C. These composites with 3:6, 3:8 and 3:12 ratio of Mg(NH2)2 and LiH have been independently reported by four groups as promising candidates of high performance hydrogen storage materials possessing the reversibility and the high capacity. In any cases, an interaction between NH3 and LiH plays an important role for the progress of hydrogen desorbing and absorbing reactions. For the hydrogen desorption process, the NH3 molecule generated from Mg(NH2)2 reacts with LiH, forming LiNH2 and H2. Especially, under an equilibrium condition, in situ diffraction results indicated that the single phase of LiNH2·MgNH (LiMgN2H3) could be generated other than the separated two phases. As a next step, the NH3 molecule generated from LiNH2 reacts with LiH, desorbing H2. As a result, the dehydrogenated phase was evaluated to be Li2NH·MgNH (Li2MgN2H2) or separated two phases, in which the final phase should depend on the experimental conditions. Thus, if the amount of LiH is enough to react with NH3, the hydrogen desorption processes are described by the NH3 generation from the corresponding amides and the imide. 相似文献
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Sintering of cubic boron nitride (cBN) with addition of A1 is carried out in the temperature range 1300-1500℃ and under the pressure 5.5 GPa. When sintered at 1300℃, a weak diffractive peak of hexagonal BN (hBN) is observed in the Al-cBN sample, indicating the transformation from cBN to hBN. No nitrides or borides of A1 are observed, which indicated that A1 does not react with cBN obviously. When the sintering temperature is increased to 1400℃, the diffractive peak of hBN disappears and new phases of A1N and A1B2 are observed, due to reactions between A1 and cBN. When the sintering temperature is further increased to 1500℃, the contents of A1N and A1B2 phases increase and the A1 phase disappears completely. 相似文献