共查询到20条相似文献,搜索用时 93 毫秒
1.
2.
掺杂分子晶体NH_(4-x)D_xNO_3相变中的分形行为──NO_3~-u_1、u_4振动模临界态拉曼峰强的研究马树国,吴国祯(清华大学物理系北京100084)TheFractalInterpretationofthePhaseTrasitionof... 相似文献
3.
本文用第一原理的LDF-LMTO-ASA方法,以超元胞Ba4Bi4O(12),(Ba3K)Bi4O(12),(BaK)Bi2O6,(BaK3)Bi4O(12),K2Bi2O6五种“样本”计算由于Bi(+3)和Bi(+5)二种价态以及K掺杂引起各芯态能级化学位移的变化.“样本”的电子结构与实验相符,即Ba4Bi4O(12)是Eg=2.0eV的半导体,(Ba3K)Bi4O12是Eg=1.6eV其价带顶有少量空穴的半导体.其余“样本”是金属.芯态的LDF本征值经原子模型△SCF修正更接近实验值.用正态分布表达各芯态能级除化学位移外各种“环境因子”的影响,结合任意组份五种“样本”的伯努利分布,计算芯态电子能谱随x的变化.结果表明,所有芯态的自旋一轨道分裂与实验完全相符,Bi(+3)和Bi(+5)二种价态引起各芯态化学位移的变化均小于0.2eV,K掺杂使各芯态结合能略有增加,其中Bi(4f),Ba(5d)约1.3~1.5eV,其他芯态约0.4eV,以上计算结果与实验基本一致. 相似文献
4.
5.
LIU Shutian 《Chinese Journal of Lasers》1995,4(3):275-280
OpticalAssociativeMemoryBasedonDoublePhaseConjugationUsingBi_(12)TiO_(20)PhotorefractiveFiber¥LIUShutian(DepartmentofPhysics,... 相似文献
6.
用第一原理的LDFLMTOASA超元胞法,模拟由X射线吸收谱精细结构测定的BaBiO3中,Bi有两种价态Bi3+和Bi5+及与之相应的两种不同键长的Bi—O八面体,以及K掺杂对晶体结构的影响.计算了Ba4Bi4O12,(Ba3K)Bi4O12,(BaK)Bi2O6,(BaK3)Bi4O12,K2Bi2O6(简记为(404),(314),(112),(134),(022))五种“样本”的电子结构.结果表明,(404)和(314)分别为Eg=16eV及Eg=15eV的半导体,其它“样本”为金属.总能的分析表明(134)是不稳定的,故溶解极限为x=05.以“取样”方式按伯努利分布确定任意组分各“样本”的概率,进而计算了(Ba1-xKx)BiO3电子结构随组分的变化.最后用逾渗模型说明了超导转变温度Tc在x=0.25附近的突变 相似文献
7.
本用第一原理的LDF-LMTO-ASA方法,以超元胞Ba4Bi4O12,(Ba3K)BiO12,(BaK)Bi2O6,(BaK3)Bi4O12,K2Bi2O6五种“样本”计算由于Bi^+3和Bi^+5二种价态以及K掺杂引起各芯态能级化学位移的变化,“样本”的电子结构与实验相符,即Ba4Bi4O12是g=-2.0eV的半导体,(Ba3K)Bi4O12j Eg=1.6eV其价带顶有不量空穴的半导体, 相似文献
8.
9.
在0.0001-2.4GPa流体静压力范围详细研究了非晶(Fe_xCo_x)_(77.5)Nd_4B_(18.5)(0≤x≤1.0)合金的电阻率与压力的关系,得到该非晶合金电阻率的压力系数随组分x变化的规律。结果表明:用少量的钴(x=0.2)替代铁,不会影响其硬磁性和热稳定性,同时却可减小电阻率的压力系数,从而增强电磁性能在压力下的稳定性。此外还观测到在0.51GPa保压3-24b的结构弛豫,进一步求出该非晶台金电阻率的压力弛豫时间对组分x的依赖关系。 相似文献
10.
在通常的ZnO-Bi_2O_3-Sb_2O_3系电压敏陶瓷中,加入能构成压敏特性的钡添加剂,发现除已知的Bi_2O_3和Zn_2.33Sb_0.67O_4晶界相以外,还出现新的晶界相,分析表明是固溶有微量其它成分的偏锑酸钡(BaSb_2O_6)晶相。同时还发现,BaSb_2O_6相是热稳定的,它对改善压敏陶瓷的退降性能起重要作用。通过控制各种添加剂的含量,使晶界相Bi_2O_3,Zn_2.33Sb_0.67O_4和BaSb_2O_6之间的数量有适当比例时,压敏陶瓷在长期电负荷作用下和脉冲大电流作用下的抗退降能力都有显著的提高,特别可贵的是反向V—I特性的退阵有很大的改善。 相似文献
11.
Polycrystalline samples of Fe-modified PLZT (lead lanthanum zirconate titanate) are prepared by a mixed-oxide reaction technique.
The formation of the compound has been confirmed by X-ray powder diffraction studies. The unit cell structure of the material
has been found to be rhombohedral. Fourier-transform infrared reflection (FTIR) spectra have been recorded to correspond the
structural changes associated with the phase formation. The effects of Fe concentration on the microstructure and dielectric
constant of PLZT materials have been investigated. The ferroelectric phase transition of PLFZT materials is studied using
dielectric measurements, which shows a shift in the transition temperature towards the higher-temperature side with increased
Fe ion concentration. The piezoelectric constants of this system are investigated by the same way of changed contents of Fe
ion in the main PLZT compound. The optimum values of Qm, kp, and d33 are 73, 0.32 and 406. The electrical conductivity increases with the increase in Fe ion concentration.
PACS 77.80.Bh; 77.84.Dy; 77.22.Ch; 72.15.Eb; 06.60.Ei; 39.30.+w 相似文献
12.
Casanueva Marenco MJ Fowley C Hyland BW Galindo-Riaño D Sahoo SK Callan JF 《Journal of fluorescence》2012,22(3):795-798
A simple fluorescent sensor 1 has been developed for the recognition of Fe(III) in semi-aqueous solution at pH 7.0. The sensor, containing two Schiff base
type receptors directly connected to naphthalene fluorophores, shows a concentration dependent decrease in emission intensity
upon Fe(III) addition. The sensor was selective for Fe(III) over other metal ions and can measure Fe(III) ion concentration
between 0.05 and 0.12 mM. The binding stoichiometry was established as 1:1 (host: guest) with a binding constant (Logβ) of
4.01. Furthermore, the addition of Fe(III) to a solution of 1 caused a colour change from light yellow to colourless meaning 1 is also capable of detecting Fe(III) by the naked eye. 相似文献
13.
Simultaneous LEED and AES are used to follow early stages of oxidation of monocrystalline FeCr(100) and (110) between 700 and 900 K in the oxygen pressure range 10?9–10?6 Torr. A chromium-rich oxide region at the alloy/oxide interface is observed, which exhibits different surface structures on oxidized FeCr(100) and FeCr(110). The chromium concentration in this initially formed oxide film is found to be enhanced by low oxygen pressures or high temperatures. During further oxidation different behaviours are observed on FeCr(100) and FeCr(110), which are explained by assuming different ion permeabilities through the initial chromium rich oxide regions on the two surface planes. On FeCr(110) surfaces oxidation is initiated on chromium enriched (100) facets at 800 K or below. At 900 K a film consisting of rhombohedral Cr2O3 or (Fe, Cr)2O3 is epitaxially growing with its (001) plane parallel to the alloy (110) face. On FeCr(100) surfaces the chromium rich oxide region next to the substrate is of fcc type. As soon as the diffusion of iron from the alloy to the gas/oxide interface is observable, a spinel type oxide is formed and connected with the location of iron in tetrahedral lattice sites. Closer to the fcc lattice the spinel oxide consists of FeCr2O4 or a solid solution of FeCr2O4 and Fe3O4 whereas next to the gas phase the oxide is pure Fe3O4. 相似文献
14.
15.
Kato K Moritomo Y Takata M Sakata M Umekawa M Hamada N Ohkoshi S Tokoro H Hashimoto K 《Physical review letters》2003,91(25):255502
The charge density distribution has been determined for a transition metal cyanide, RbMn[Fe(CN)(6)], by means of the maximum entropy-Rietveld method combined with the highly angularly resolved synchrotron radiation x-ray powder diffraction at SPring-8 BL02B2. We directly observed a charge transfer from the Mn site to the Fe site in the low-temperature phase. On the basis of a local density approximation calculation, we discuss the origin for the anisotropic bonding electron distribution around the Mn3+ ion in the low-temperature phase. 相似文献
16.
The effect of Al substitution for Fe on crystal structure, magnetostriction and spontaneous magnetostriction, anisotropy and spin reorientation of a series of polycrystalline Tb0.3Dy0.7(Fe1-xAlx)1.95 alloys (x = 0, 0.05, 0.1, 0.15, 0.20, 0.25, 0.30, 0.35) at room temperature and 77 K was investigated systematically. It was found that the primary phase of Tb0.3Dy0.7(Fe1-xAlx)1.95 is the MgCu2-type cubic Laves phase structure when x < 0.4 and the lattice constant a of Tb0.3Dy0.7(Fe1-xAlx)1.95 increases approximately and monotonically with the increase of x. The substitution of Al leads to the fact that the magnetostriction ( inceases slightly in a low magnetic field (H ≤ 40 kA/m), but decreases sharply and is easily close to saturation in a high applied field as x increases, showing that a small amount of Al substitution is beneficial to a decrease in the magnetocrystalline anisotropy. It was also found that the spontaneous magnetostriction (ζ)111 decreases greatly with x increasing. The analysis of the M(o)ssbauer spectra indicated that the easy magnetization direction in the {110} plane deviates slightly from the main axis of symmetry with the changes of composition and temperature, namely spin reorientation. A small amount of non-magnetic phase exists for x = 0.15 in Tb0.3Dy0.7(Fe1-xAlx)1.95 alloys and the alloys become paramagnetic for x > 0.15 at room temperture, but at 77 K the alloys still remain magnetic phase even for x = 0.2. At room temperature and 77 K, the hyperfine field decreases and the isomer shifts increase with Al concentration increasing. 相似文献
17.
The chemisorption and decomposition of propyne on clean Fe(110) and Fe(100) surfaces have been studied by ultraviolet photoelectron spectroscopy (UPS). The UPS spectra suggest that exposure at 78 K produces chemisorbed propyne on both these surfaces, while excess exposure of the adsorbate produces a condensed propyne phase at the same temperature. Upon warming to ~100 K, the condensed phase disappears and the chemisorbed phase appears again on both the surfaces. Further warming to ~170 K produces a dissociatively adsorbed propyne phase on Fe(100), and the spectral features then scarcely change for further warming to ~370 K. In the case of Fe(110), on the other hand, the chemisorbed phase is apparently unchanged by heating even up to ~370 K. All peaks due to chemisorbed propyne on both Fe(110) and Fe(100) disappear at ~470 K, with the formation of carbonated surfaces. 相似文献
18.
I. V. Ovchinnikov T. A. Ivanova V. E. Petrashen’ Yu. G. Galyametdinov G. I. Ivanova 《Applied magnetic resonance》2005,29(2):325-334
The low-spin (LS) to high-spin (HS) transition in two mesogenic Fe(III) complexes with alkyloxysalicyliden-N′-ethyl-N-ethylendiamine as ligands is studied by electron paramagnetic resonance (EPR). The symmetrization of the crystal
field around the Fe(III) ion under first heating of a polycrystalline sample from the room temperature was observed in the
spectra of HS complexes. The line narrowing (from 45 to 15 mT) under the crystal-smectic phase transition is explained by
the strengthening of the intermolecular exchange interaction, as a result of the structural reorganization of layers in the
smectic phase. A feature of both mesogenic spin-transition systemsis an unusual field-induced spin instability which leads
to the hysteresis of the HS-LS composition. This instability is detected by EPR and magnetic susceptibility methods. The alignment
of systems by magnetic field in the mesophase and a complete or partial orientational order under cooling the mesophase to
the glass state are the main reason for this hysteresis. The influence of EPR-silent LS complexes reveals itself in the line
broadening of HS compounds’ when the temperature is lowered from 220 K. 相似文献
19.
Snehal Jani Varkey Sebastian N. Lakshmi V. R. Reddy K. Venugopalan Ajay Gupta 《Hyperfine Interactions》2008,185(1-3):23-28
Fe/Al multilayer thin films prepared by ion beam sputtering, with an overall atomic concentration ratio of Fe/Al = 1:2 have been studied by x-ray diffraction spectroscopy (XRD), X-ray reflectivity (XRR) and D.C. Magnetization. These studies show the formation of Fe–Al intermetallic layers. Two magnetic regions and transition temperatures of 473 and 533 K are evident from magnetization studies. Conversion Electron Mössbauer Spectroscopy (CEMS) shows formation of off-stoichiometric Fe3Al like phase and phases consisting of pure Fe and Fe-rich extended Fe–Al solutions. 相似文献
20.
光度法研究聚乙二醇-硫酸铵-邻苯三酚红体系中铋(Ⅲ), 铁(Ⅲ), 铜(Ⅱ), 镍(Ⅱ), 钴(Ⅱ), 铅(Ⅱ)的萃取分离 总被引:6,自引:0,他引:6
本文研究了在聚乙二醇(PEG)-硫酸铵[(NH_4)_2SO_4]-邻苯三酚红(PR)体系中Bi(Ⅲ),Fe(Ⅲ),Cu(Ⅱ),Ni(Ⅱ),Co(Ⅱ),Pb(Ⅱ)的萃取行为。实验结果表明,Bi(Ⅲ)在pH3.5~6.5及Fe(Ⅲ)在pH4.0~7.0范围内可以被PEG相几乎完全萃取,而Cu(Ⅱ),Co(Ⅱ)在pH1.0~7.0,Pb(Ⅱ)在pH2.0~7.0,Ni(Ⅱ)在pH1.0~4.5则不被萃取。从而实现了将Bi(Ⅲ)(pH3.5),Fe(Ⅲ)(pH5.0)与Cu(Ⅱ),Co(Ⅱ),Pb(Ⅱ),Ni(Ⅱ)混合离子的定量分离。同时探讨了PEG相的萃取机理。 相似文献