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采用高温固相法合成Sr_(1.98)(Al_(1–x) Mg_x)(Al_(1–x) Si_(1+x))O_7: 2%Eu~(2+)荧光粉完全固溶体,利用X射线衍射、光致发光光谱和光学显微镜进行晶体结构和发光性能的研究. Sr_2Al_2SiO_7和Sr_2MgSi_2O_7同构化合物中包含[MgO_4]、[SiO_4]和[AlO_4]四面体,较大体积的[MgO_4]和较小体积的[SiO_4],共同替代体积相似的[AlO_4],导致[(Si/Al)O_4]收缩和[(Mg/Al)O_4]膨胀,晶胞参数c减少, a和V增大,使Eu~(2+)周围的环境发生改变,晶体场劈裂程度减小,发射峰位从503 nm蓝移至467 nm,实现发光光谱从绿色(0.2384, 0.3919)到蓝色(0.1342,0.1673)的转变.当x为0时,发射峰的半高宽为120 nm, x从0.25增加到1时,半高宽由89 nm逐渐减小至50 nm,多面体的替代会改变荧光粉的发光性能. 相似文献
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提出利用S-RESIDOR(Symmetry-based Resonance Echo Saturation Irradiation DOuble Resonance)方法测量1H-27Al偶极偶合常数. 通过理论模拟,讨论了四极作用常数、饱和照射脉冲功率、照射时间对1H/27Al S-RESIDOR实验的影响. 发现四极作用常数对1H/27Al S-RESIDOR偶极去相曲线影响较小,中等强度的饱和照射功率即能满足实验要求. 高转速下,在氢型丝光沸石上进行了1H/27Al S-RESIDOR实验,测量得到Br-nsted酸位上的 1H与骨架上27Al的偶极偶合常数为874 Hz. 相似文献
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高岭土与针铁矿胶结样中27Al、29Si NMR谱与其原子电荷关系 总被引:3,自引:0,他引:3
由NMR谱实验得高岭土与针铁矿胶结样中27Al、29Si的化学位移较单一高岭土分别正移了2.7ppm和2.33ppm.由CNDO/2方法计算得到胶结样中Al、Si原子电行比高岭土分别减少了0.0787和0.0286.胶结样中Al、Si原子电荷的减少与27Al、29Si NMR谱化学位移相吻合,可以认为在高岭土与外铁矿的界面上形成了氢键而呈现胶结态. 相似文献
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采用高温原位拉曼光谱技术,研究了Li2B4O7从常温至1 373 K温度范围内的拉曼光谱。在升温过程中,晶体的拉曼光谱出现展宽和红移现象,且强度降低。晶体熔化时,由2个[BO4]和2个[BO3]组成的[B4O9]环状结构转变成(B3O6)3- 六元环和[BO3]结构,[BO4]结构减少直至消失。基于密度泛函理论,计算了Li2B4O7晶体的拉曼光谱,对其振动模式进行了分析归属。利用量子化学从头计算法计算了由[B3O6-BO3]为基础相互连接形成的x(Li2B4O7)(x=2, 3, …, 9)的环状团簇模型的拉曼光谱,对Li2B4O7熔体的结构进行了模拟分析。计算结果表明Li2B4O7熔体的阴离子基元为三个(B3O6-BO3)组成的大三元环超级结构。 相似文献
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Y型沸石脱铝机制和铝状态的NMR研究 总被引:2,自引:2,他引:0
对Y型沸石原粉及几种不同脱铝样品进行了几种不同NMR方法的测量,确定了不同处理过程的脱铝机制和骨架内外铝状态的变化,29Si MAS NMR谱给出了骨架Si、Al分布的信息,反映了不同方法处理样品其脱铝机制的差异,据此可以控制Y沸石脱铝过程获得更高的硅铝比,27Al MAS NMR谱、二维章动NMR及1H-27Al CP/MAS NMR测量表明:水热处理的Y沸石中存在4种不同的铝状态。综合29Si和27Al MAS NMR观测,可相当程度地推断Y型沸石分子筛脱铝改性所发生的内部过程。 相似文献
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3-[5-(α-萘)-2H-四唑-2-甲撐-4-苯基-1,2,4-三唑啉-5-硫酮13C-NMR的研究 总被引:2,自引:1,他引:1
本文研究了5-(α-萘)-四唑(Ⅱ),5-(α-萘)-2H-四唑-2-乙酸甲酯(Ⅲ),5-(α-萘)-2H-四唑-2-乙酰肼(Ⅳ),1-[5-(α-萘)-2H-四唑-2-乙酰]-4-苯基氨基硫脲(V)以及3-[5-(α-萘)-2H-四唑-2-甲撐]-4-苯基-1,2,4-三唑啉-5-硫酮(Ⅵ)的13C核磁共振谱和各种13C-NMR化学位移。根据化学位移理论、讯号强度以及同模型化合物化学位移的比较,辨认其归属。 相似文献
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Neutron diffraction study of polycrystalline HoRu2Si2, HoRh2Si2, TbRh2Si2, and TbIr2Si2 was performed in the temperature range between 4.2 and 300 K. For HoRu2Si2 the magnetic spin alignment of a linear transverse wave mode below the Néel temperature 19 K is observed. This static moment wave is propagating along the b-axis with k=(0, 0.2, 0) and is polarized in the c-axis. The root-mean-square and maximum saturation moments per Ho atom are 9.26 and 13.09μB, respectively. HoRh2Si2, TbRh2Si2 an TbIr2Si2 are simple collinear antiferromagnets of +-+- type with Néel temperatures of (27±1), (98±2) and (72±3) K, respectively. For TbRh2Si2 and TbIr2Si2 magnetic moments are localized on RE ions only and are aligned along the tetragonal axis, while for HoRh2Si2 they form an angle ø = (28±3)°. 相似文献
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P. Dalmas de Réotier B. Licciardi A. Yaouanc B. Chevalier P. Chaudouët R. Madar J. P. Sanchez 《Hyperfine Interactions》1990,59(1-4):317-320
Muon spin relaxation experiments have been carried out in the paramagnetic and magnetically ordered states of URh2Si2 and CeRh2Si2. As the magnetic structure of these compounds is well known, these measurements can help to characterise their magnetic properties
probed by μSR and to understand the μSR results of the heavy fermion compounds of the same crystallographic family. Our measurements
show that the muons occupy two different crystallographic sites. The spectra of URh2Si2 and CeRh2Si2 in the magnetically ordered states are very different, probably reflecting their different magnetic structures. The spectra
obtained on CeRh2Si2 are similar to the published spectra of the heavy fermion compound CeCu2.1 Si2. Muon spin rotation measurements on LaNi2As2 indicate that the muon is diffusing at 150 K. 相似文献
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The CO2 TEA laser irradiation of CBr2F2 in the presence of Cl2 yielded 13C-enriched CBrClF2 and 13C-enriched CCl2F2 under selected experimental conditions. As the photolysis proceeded, the 13C concentration of CBrClF2 decreased gradually and that of CCl2F2 increased up to 90% or higher. These results can be explained by the mechanism involving the secondary 13C-selective IRMPD of the primary product CBrClF2. On the other hand, the carbon-containing product for a CCl2F2/Br2 system was only CBrClF2; the further IRMPD of which probably regenerated CBrClF2 in the presence of Br2. The decomposition probabilities of 12C- and 13C-containing molecules in both systems were measured as functions of laser line, laser fluence, and reactant pressures. 相似文献
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Guo Guanghua R. Z. Levitin V. V. Snegirev D. V. Filippov 《Physics of the Solid State》2001,43(3):496-500
Longitudinal and transverse magnetostrictions of polycrystalline samples of intermetallic compounds RMn2Ge2 (R=Sm or Gd) are measured in pulsed magnetic fields up to 250 kOe. It is found that linear magnetostrictive strains of about 10?3 arise in a temperature range in which the magnetic field causes a change in the magnetic state of a manganese magnetic subsystem. The results obtained are described within the model of a two-sublattice ferrimagnet with a negative exchange interaction in the manganese subsystem in terms of a strong dependence of this interaction on interatomic distances. 相似文献
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J. Petzelt I. Mayerová Č. Bárta L. D. Kislovskii 《Czechoslovak Journal of Physics》1973,23(8):845-854
Far infrared (30–430 cm?1) reflectivity measurements of Hg2Cl2 and Hg2Br2 single crystals have been performed in polarized light. The spectra, which are in agreement with group-theoretical predictions, were analyzed by the oscillator fitting procedure and Kramers-Kronig method. The results are compared with the existing data from other measurements and the large anisotropy of polar modes is briefly discussed. The polarization vectors of all long-wavelength symmetry modes were determined group-theoretically. 相似文献
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《中国科学:物理学 力学 天文学(英文版)》2018,(12)
正Since the discovery of superconductivity in LaFeAsO_(1-x)F_x,the high-T_c iron-based superconductors have been extensively studied from both experimental and theoretical viewpoints [1-8]. However, the mechanism of the unconventional superconductivity is still to be resolved. To 相似文献
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H. Oesterreicher 《Journal of Physics and Chemistry of Solids》1973,34(7):1267-1280
Both pseudobinary systems exhibit large homogeneous regions of cubic and hexagonal Laves phases. Ordering tendencies on crystallographic sites between Al and the transition metals are observed in the hexagonal type.Electron transfer to the transition metals quenches their moments so that they become nonmagnetic at high Al concentrations. The peculiarities in the mechanism of magnetization which appear in rare earth dialuminides when Al is replaced by a transition metal have been studied in detail at cryogenic temperatures.The first replacement of Al results in a decrease in saturation moment. Neutron diffraction verifies the low ordered rare earth sublattice moments and reveals the ‘lost part’ as a disordered component. Considerable magnetic hardness develops in certain regions of concentration often connected with spontaneous increases in magnetization with field. All available evidence suggests the presence of unusual domain wall effects to be responsible for this effect. High remanences develop in both the hexagonal and in the cubic structures in the intermediate region. The development of disordered magnetic components is connected either with the disorder on crystallographic sites or changes in the free electron concentration. 相似文献