Oxidation of Si(100)2x1 and Gex Si1−x (100)2x1

High resolution electron energy loss Spectroscopy (HREELS), X-ray photoelectron Spectroscopy (XPS) and low energy electron diffraction (LEED) have been used to characterize initial stages of oxidation of Si(100)2x1 and Ge_x Si_1−x (100)2x1 surfaces. Different oxidation stages of Si were identified by measuring Si 2p core level shifts and characteristic vibrations of Si-O-Si complexes. The latter may be described in the framework of continuous random network models.Then,from the experimentally determined frequencies, force constants,average bond angles and bond lengths are determined. Complementary,marker experiments with atomic hydrogen as a probe in conjunction with HREELS were used to determine the local, atomic structure for different stages of oxidation from chemical shifts of Si-H and Ge-H stretching mode intensities, respectively.     

Thermoelectric power of Ba(Fe1−x Co x )2As2 (0 ≤ x ≤ 0.05) and Ba(Fe1−x Rh x )2As2 (0 ≤ x ≤ 0.171)

Temperature-dependent, in-plane, thermoelectric power data are presented for single crystals of Ba(Fe_1?x Co _x )₂As₂ (0?≤?x?≤?0.05) and Ba(Fe_1?x Rh _x )₂As₂ (0?≤?x?≤?0.171). Given that previous thermoelectric power and angle resolved photoemission spectroscopy studies of Ba(Fe_1?x Co _x )₂As₂ delineated a rather large Co-concentration range for Lifshitz transitions to occur, and the underdoped side of the phase diagram is poorly explored, new measurements of thermoelectric power on tightly spaced concentrations of Co, 0?≤?x?≤?0.05, were carried out. The data suggest evidence of a Lifshitz transition, but instead of a discontinuous jump in thermoelectric power in the range 0?≤?x?≤?0.05, a more gradual evolution in the S(T) plots as x is increased was observed. The thermoelectric power data of Ba(Fe_1?x Rh _x )₂As₂ show very similar behavior to that of Co substituted BaFe₂As₂. The previously outlined T–x phase diagrams for both systems are further confirmed by these thermoelectric power data.     

Spectral luminescence properties of Ca1 ? x Sr x F2:Ce3+ (0 < x <1) crystals

The luminescence, reflection, and luminescence excitation spectra of two-component Ca_{1 ? x} Sr _x F₂:Ce³⁺ (0.05 mol %) (x = 0.14, 0.25, 0.4, 0.6, and 0.75) have been studied at room temperature and T = 8 K. It is shown that the luminescence bands (upon 130-eV photon excitation) in the range of 200 to 400 nm are attributed to singlet and triplet self-trapped exciton luminescence and to 5d-4f transitions in Ce³⁺.     

SrAl_(2x)O_(3x+1):Eu~(2+),Dy~(3+)(x=1～2)合成及其余辉特性分析

通过调节基质组份比例,研究了SrAl2xO3x+1∶Eu2+,Dy3+(x=1~2)荧光粉晶体结构,发光性质及长余辉特性。选取硝酸锶和硝酸铝作为基质原材料,硼酸氨和氟化铝作为助溶剂,采用阳离子草酸盐共沉淀,湿法预先混合原材料及分步合成等方法,制备了亮度高、余辉长及良好粒径分布的系列长余辉发光材料。基于对样品X射线衍射(XRD)图谱,扫描电子显微镜(SEM)照片,激发、发射光谱及余辉衰减曲线分析,发现SrAl2xO3x+1∶Eu2+,Dy3+具有良好的结晶状态;随x增加,发射光谱峰值从520 nm蓝移至470 nm;衰减到可辨认发光强度0.32 mcd/m2,余辉时间可相应地从30 h延长到60 h以上。通过分析发现表现不同余辉特性的主要原因是Eu2+在基质中具有不同浓度、不同衰减寿命的蓝、绿两种发光中心造成的,其中蓝发光中心寿命明显高于绿发光中心。     

双层钙钛矿锰氧化物Nd_(2-2x)Ca_(1+2x)Mn_2O_7(x=0.4,0.5)的磁相变特性

利用固相反应法制备了Nd2-2x Ca1+2x Mn2O7(x=0.0-0.9)多晶样品,通过FULLPROF程序对样品X射线衍射图谱进行了精修,样品的空间群为14/mmm.测量了样品x=0.4,0.5的磁性(5K相似文献   

粉末晶体(ZrO2)x(Bi2O3)1-x(x=1.0, 0.97) 晶体结构分析

为了确定ZrO2和(ZrO2)0.97(Bi2O3)0.03的晶体结构和原子热振动各向同性温度因子B,对该粉末晶体进行X射线衍射实验,建立了晶体结构模型,进行晶体结构分析。首先,采用共沉淀法和高温固相烧结法制备了纳米氧化锆ZrO2和(ZrO2)0.97(Bi2O3)0.03粉末晶体,接着,使用X射线测试仪对两种样品进行了衍射实验（XRD）,利用Rietveld 精修方法的 RIETAN-2000程序对所得实验结果进行了晶体结构分析,获得了晶体结构参量和原子热振动各向同性温度因子B。通过Maximum Entropy Method（MEM）解析得到了粉末晶体(ZrO2)x(Bi2O3)1-x(x=1.0,0.97)的等高电子密度分布可视化图谱。结果表明,(ZrO2)0.97(Bi2O3)0.03的晶胞体积比ZrO2的晶胞体积大分别为140.6850 Å3和140.5637Å3;ZrO2晶体的原子热振动各向同性温度因子B(Zr)、BO(1)、BO(2)和 B（Bi）分别为0.690、0.269、 0.178 和 0 Å2,(ZrO2)0.97(Bi2O3)0.03晶体的分别为0.460 、0.583 、0.121 和0.581 Å2。 确定了(ZrO2)0.97(Bi2O3)0.03的晶体结构属于单斜晶系,实现了等高电子密度分布三维（3D）和二维（2D）的可视化,进一步确定了晶体结构和原子位置。     

Vortex structure in BaFe2(As1 − x P x )2 single crystals

Single crystals of iron-containing Ba(FeAs)₂ superconductors doped with phosphorus have been studied. The vortex structure has been studied by means of the decoration method. Large domains of the triangular vortex structures have been observed in the phosphorus-doped single crystals of iron-containing superconductors. The effect of doping on pinning in iron-containing superconductors has been discussed.     

Neutron diffraction study of the oxide conducting δ1-phase of (Bi2O3)1−x(Y2O3)x (x=0.25)

The atomic parameters of the average cell of δ¹-Bi(Y)O_1.5 were determined by powder neutron diffraction. The evidence indicates that the disorder in the structure has many features in common with the structure of the oxygen deficient zirconia. Most oxygens (78%) are in sites displaced 0.335 Å along 〈100〉 directions from the normal fluorite positions, while a smaller proportion (22%) are displaced 0.80 Å along 〈111〉 directions and no oxygen remains in normal positions. In addition to the anion displacements a smaller displacement (0.25 Å) along the 〈111〉 direction was found for the cations. Comparison with the structure of β-Bi₂O₃ suggests that the displacements may be precursors to a δ→β phase transition.     

Elektronen-Spin-Resonanz an (La1−−x Gd y Ce x )Al2

In the EPR of (La_1––x Gd _y Ce _x )Al₂ a bottleneck in the relaxation of the conduction electrons to the lattice is present at sufficiently high Gd-concentrations. The bottleneck can be broken by decreasing the Gd-concentration or by adding Cerium as a spin-flip-scatterer.g-factor and line broadening are measured for (La_1–y Gd _y )Al₂ and (La_1––x Gd _y Ce _x )Al₂ as a function of temperature and Gd- and Ce-concentrations. The Cerium induced relaxationsrate _eL (Ce) increases linearly with Ce-concentration up tox0.025. This corresponds to the fact, well known by measurements of the Kondo anomalies, that Cerium impurities show no significant interaction up to rather high concentrations.     

High-Moment-Low-Moment Description of Magnetovolume Effects in Y(Mn x Al 1− x ) 2 and Y x Sc 1− x Mn 2

Based on the assumption of a high-moment-low-moment instability of the Mn atom, we construct a simple spin model with coupled magnetic and spatial degrees of freedom to describe the Laves phase systems Y(Mn x Al 1 m x ) 2 and Y x Sc 1 m x Mn 2 . Monte Carlo simulations of this model qualitatively reproduce anomalies observed in these materials like a discontinuous giant volume change and anomalous thermal expansion behavior.     

Ellipsometry study of interband transitions in TlGaS2xSe2(1−x) mixed crystals (0≤x≤1)

In this paper, the spectroscopic ellipsometry measurements on TlGaS_2xSe_2(1?x) mixed crystals (0≤x≤1) were carried out on the layer-plane (001) surfaces with light polarization E⊥c^? in the 1.2–6.2 eV spectral range at room temperature. The real and imaginary parts of the dielectric function, refractive index and extinction coefficient were calculated from ellipsometric data using the ambient-substrate optical model. The critical point energies in the above-band gap energy range have been obtained from the second derivative spectra of the dielectric function. Particularly for TlGaSe₂ crystals, the determined critical point energies were assigned tentatively to interband transitions using the available electronic energy band structure. The effect of the isomorphic anion substitution (sulfur for selenium) on critical point energies in TlGaS_2xSe_2(1?x) mixed crystals was established.     

Magnetic properties of U (Fe x Al1−x )2 and U(Fe y Ni1−y )2 compounds

The results of magnetic measurements and ferromagnetic resonance studies performed on U(Fe _x Al_1–x )₂ and U(Fe _y Ni_1–y )₂ compounds over a large temperature range are reported. The saturation magnetization decreases nearly linearly when substituting Fe by Al or Ni. In the composition range x<0.84 and y<0.81, the compounds are Pauli paramagnets, except in the region with y0.10. For UNi₂ two types of magnetic behaviours are shown. This compound can be both a ferromagnet withT _c =23.5 K and a Pauli paramagnet, depending on the crystal structure. Above the Curie temperatures, the reciprocal susceptibility for the compounds with x>0.84 and y>0.81 obeys a temperature dependence of the formX=X _o+C(T-) ^–1. The effective iron moments decrease when substituting iron by nickel or aluminium. The ferromagnetic resonance measurements show that theg values are not composition-dependent. A linear variation of the mean iron magnetization with the exchange field is observed. Finally, the magnetic behaviour of iron in these compounds is analysed.     

Hyperfine magnetic interactions in Tb(Fe1 − x Al x )2 alloys

The structural and magnetic characteristics of phase transformations in Tb(Fe_{1 ? x} Al _x )₂ alloys with concentrations x = 0?0.9 have been measured in the temperature range from 90 to 450 K. The temperature dependences of the hyperfine magnetic fields for each of local configurations of the nearest environment of iron atoms upon substitution of aluminum atoms for iron atoms have been found using Mössbauer spectroscopy.     

Single crystal growth and superconductivity of Ca(Fe1−x Co x )2As2

We report the single crystal growth of Ca(Fe_1?x Co _x )₂As₂ (0?≤?x?≤?0.082) from Sn flux. The temperature–composition phase diagram is mapped out based on the magnetic susceptibility and electrical transport measurements. The phase diagram of Ca(Fe_1?x Co _x )₂As₂ is qualitatively different from those of Sr and Ba; this could be due to both the charge doping and structural tuning effects associated with Co substitution.     

(Bi2O3)1-x(Sc2O3)x(x=0.01,0.03,0.05)粉末晶体的制备与晶体结构分析

采用固相烧结法制备(Bi2O3)1-x(Sc2O3)x(x=0.01, 0.03, 0.05)粉末晶体,在室温下对几种样品分别进行了X射线衍射实验,并用RIETAN-2000程序中的Rietveld解析法以及VEND、PRIMA和VICS程序分别研究了几种样品的晶体结构、等高电子密度（2D和3D）、原子配位数及原子热振动各向同性因子B等. 结果表明,(Bi2O3)1-x(Sc2O3)x(x=0.01, 0.03, 0.05)的晶胞体积（分别为329.3399Å3、329.5016 Å3、329.3400 Å3、330.3658 Å3）比Bi2O3的晶胞体积（330.3658 Å3）小;(Bi2O3)1-x(Sc2O3)x(x=0.01, 0.03, 0.05)晶体的原子热振动各向同性温度因子B(Sc1)、B(Sc2)、B(Bi1)、B(Bi2)、B(O1)、B(O2)、B(O3)的大小分别为0.42883 Å2、0.54412 Å2、0.609364 Å2、0.502542 Å2、0.4034 Å2、0.61406 Å2、0.74259 Å2;0.43052 Å2、0.52778 Å2、0.51647 Å2、0.382431 Å2、0.320327 Å2、0.516762 Å2、0.76875 Å2和0.42347 Å2、0.61022 Å2、0.514476 Å2、0.302724 Å2、0.34725 Å2、0.56175 Å2、0.72125 Å2. 确定了(Bi2O3)1-x(Sc2O3)x(x=0.01, 0.03, 0.05)粉末晶体属于单斜晶系,实现了二维和三维等高电子密度分布的可视化,进一步确定了晶体结构和原子位置.     

Mössbauer study of Y2Fe17N x (x < 3) nitrides

⁵⁷Fe Mössbauer spectra of Y₂Fe₁₇N_x nitrides were measured. The hyperfine field (H _hf) and the average isomer shift for Y₂Fe₁₇ increase obviously after nitrogenation. Forx1.1, however, the averageH _hf varies only slightly, while the increase ofH _hfat each iron site is somewhat different and more pronounced at 4f dumbbell sites than at the other sites when the nitrogen concentration is increased. This means that the influence of the nitrogen atoms on the local magnetic properties of the iron atoms depends sensitively on the configuration of the nearest-neighbor atoms around the iron atoms. The results are compared with the⁸⁹Y NMR spectra of Y₂Fe₁₇N _x .This project was supported by the National Natural Science Foundation and the State Key Magnetism Laboratory of China.     

多面体共替代对Sr_2(Al_(1–x) Mg_x)(Al_(1–x) Si_(1+x))O_7:Eu~(2+)晶体结构和发光颜色的影响

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.     

Bi_(1.9)Sb_(0.1)Sr_2Ca_2Cu_(2+x)O_y 的超导特性(x=0,0.4,0.8,1.0,1.2,1.6)

文中报道了 Bi_(1.9)Sb_(0.1)Sr_2Ca_2Cu_(2+x)O_y,系列的交流磁化率测量及 X 射线衍射结果,发现超导转变温度对于 Cu 的组份非常敏感,当 x=0.4时,样品在136.5K 出现抗磁性,其 X 射线衍射图中新相衍射峰较85K 超导相的峰更强,因此 Cu 的价态和配位数在形成高和 T_c 超导相中起着至关重要的作用.     

Magnetic behaviour of U(MnxAl1−x)2 compounds

The results of magnetic measurements performed on U(Mn_xAl_1−x)₂ compounds in the temperature range 4.2K < T < 800K are reported. In the low temperature range (T < 200K), UMn₂ shows a Pauli-type paramagnetism. Above 420K a Curie-Weiss behaviour is evidenced. The magnetic properties of U(Mn_xAl_1−x)₂ compounds were analysed assuming a superposition of a temperature dependent term on a Pauli-type contribution, χ_O. The effective moments as well as the χ_O values were determined both in the low (T < 200K) and high (T > 420K) temperature range. The experimental data were discussed considering changes in the band structure and/or quenching of spin fluctuations.