Photoelectron spectra of As4S3, P4S3, P4Se3 and As4O6

The He(I) UV photoelectron spectra of As₄S₃, P₄S₃, P₄Se₃ and As₄O₆ are reported in this paper. The spectra of As₄S₃ and the isostructural molecules P₄S₃ and P₄Se₃ comprise seven broad but clearly defined peaks, whilst the spectrum of As₄O₆ consists of six peaks and two shoulders. By comparing the spectra with one another and with the photoelectron spectra of other arsenic and phosphorus compounds, the character and symmetry species of the highest-energy occupied molecular orbitals of the molecules have been assigned.     

Magnetoresistance of Fe3O4/Au/Fe3O4 and Fe3O4/Au/Fe spin-valve structures

A detailed study of the in-plane magnetotransport properties of spin valves with one and two Fe₃O₄ electrodes is presented. Fe₃O₄/Au/Fe₃O₄ spin valves exhibit a clear anisotropic magnetoresistance in small magnetic fields but no giant magnetoresistance (GMR). The absence of GMR in these structures is due to simultaneous magnetization reversal in the two Fe₃O₄ layers. By contrast, a negative GMR effect is measured on Fe₃O₄/Au/Fe spin valves. The negative GMR is attributed to an electron spin scattering asymmetry at the Fe₃O₄/Au interface or an induced spin scattering asymmetry in the Au interfacial layers.     

Coupled magnetic cycloids in multiferroic TbMnO3 and Eu3/4Y1/4MnO3

Based on the detailed Mn L(2,3)-edge x-ray resonant scattering results, we report a new complexity in the magnetic order of multiferroic orthomangnites, which has been considered as the simple A-type cycloid order inducing ferroelectricity. The Dzyaloshinskii-Moriya interaction involved in the orthorhombic distortion brings on F-type canting from the A type, and the ordering type becomes the off-phase synchronized bc cycloid in TbMnO(3) or the tilted antiphase ab cycloid in Eu(3/4)Y(1/4)MnO(3). The F-type canting is responsible for the magnetic field-driven multiferroicity to weak ferromagnetism transition.     

Li4SiO4-Li3VO4赝二元系和Li4GeO4-Li4SiO4-Li3VO4赝三元系中新的锂离子导体

本文在室温到300℃的温度范围内研究了Li₄SiO₄-Li₃VO₄和Li₄GeO₄-Li₄SiO₄-Li₃VO₄体系中的离子导电性,发现γ_II相固溶体Li_3+xV_1-xSi_xO₄是好的锂离子导体。所研究的成分中Li_3.3V_0.7Si_0.3O₄的离子电导率最高,室温下为1×10^-5Ω^-1·cm^-1,在42—192℃的电导激活能为0.36eV,电子电导率可以忽略,因而这是迄今所发现的最好的锂离子导体之一。粗略确定了Li₄GeO₄-Li₄SiO₄-Li₃VO₄三元系中电导率高的范围,发现在Li_3.5V_0.5Ge_0.5O₄中Si部分取代Ge可以使电导率进一步提高,Li_3.5V_0.5Ge_0.4Si_0.1O₄的室温电导率可达1.3×10^-5Ω^-1·cm^-1,电导激活能为0.40eV。 关键词：     

β-C3N4,β-Si3N4和β-Ge3N4的能带结构

采用基于密度泛函理论的线性丸盒轨道原子球近似(LMTO-ASA)从头计算方法,研究了β-C₃N₄,β-Si₃N₄和β-Ge₃N₄的能带结构,得到了它们的能隙分别为:4.1751,5.1788和4.0279eV。对于β-C₃N₄,由于N的部分2p电子占据了非键轨道,禁带宽度较窄;对于β-Si₃N_{4关键词：}     

Electric and magnetic behaviour in double doped La2/3＋4x/3Sr1/3-4x/3Mn1-xMgxO3

The double-doped La2/3＋4x/3Sr1/3-4x/3Mn1-xMgxO3 samples with fixed Mn^3＋/Mn^4＋ ratio equal to 2/1 are investigated by means of magnetism and transport measurements. Phase separation is observed at temperature higher than T^onset c for x = 0.10 and 0.15. For x = 0.10, rather strong phase separation induces drastic magnetic random potential and results in the localization of carriers. Thus, the varlable-range hopping process dominates. For other samples, there is no or only weak phase separation above T^onset c. Thus, thermal activation mechanism is responsible for the high temperature transport behaviour. For x = 0.20 and 0.25, unexpected AFM behaviour is observed at low temperature. All these results are well understood by considering the special role of the ＂double-doping＂.     

The 4s~24p~3—4s4p~4 transition in Cd ⅩⅥ

The available experimental energies for the 4s~24p~3 and 4s~4p~4 configurations in As Ⅰ—like Sr Ⅵ—Ag Ⅹ Ⅴions are compared with the values calculated using the Hartree—Fock method including configuration interaction and relativistic corrections. Some energy values of the 4s~24p~3 configuration in Rh Ⅹ Ⅲ、Pd Ⅹ Ⅳ and Ag Ⅹ Ⅴ ions are improved and all the energies、wavelengths and transition probabilities of the 4s~24p~3—4s4p~4 transition array in Cd Ⅹ Ⅵ are presented.     

Electronic properties of Th3As4U3As4 solid solutions

(Th_xU_1?x)₃As₄ solid solutions were obtained in the range 1 ≥ x ≥ 0.85 by the modified Van Arkel method. Their resistivity, thermopower and Hall constant were determined in temperatures 4.2—700 K. The condition of impurity band formation, its merging with conduction band, as well as location of the 5?-electron states have been discussed.     

Characterization of nonstoichiometric nickel manganite spinels NixMn3−x□3δ/4O4+δ by temperature programmed reduction

Cation deficient spinels Ni_xMn_3−x□_3δ/4O_4+δ (0≤x≤1) have been prepared by thermal decomposition of mixed oxalates Ni_x/3Mn_(3−x)/3(C₂O₄)·nH₂O in air at 623 K. They have been characterised by temperature programmed reduction (TPR) under H₂, the reaction being followed by gravimetric and powder X-ray diffraction measurements. It has been shown that TPR proceeds in several steps. The first steps correspond to the loss of nonstoichiometric oxygen leading to the formation of a stoichiometric oxide. During the following stages the manganese cations are reduced, causing the spinel structure to be destroyed, and the formation of solid solution of NiO in a cubic MnO. Subsequently, Ni²⁺ cations undergo a reduction to metallic nickel, and, finally, a mixture of nonstoichiometric MnO_1−δ and metallic nickel is formed. These oxides contain a high level of vacancies which vary with the nickel content with a maximum of δ≈1 near x=0.6. This nonstoichiometry is ascribed both to the presence of Ni³⁺ and excess of Mn⁴⁺.     

Li3VO4-Li4SiO4-Li4GeO4赝三元系相图的研究

本文用差热分析法和高温、室温X射线衍射法对Li₃VO₄,Li₄SiO₄的相变过程,Li₃VO₄-Li₄SiO₄,Li₃O₄-Li-4GeO₄赝二元系相图以及Li₃VO₄-Li₄SiO₄-Li₄GeO₄赝三元系相图室温截面进行了研究。发现在Li₃VO₄-Li₄SiO₄,Li₃VO₄-Li₄GeO₄赝二元系中,由于Li₄SiO₄或Li₄GeO₄的加入而使Li₃VO₄的高温γ_II相稳定存在于室温,从而得到一种新的具有高电导率的锂离子导体。作者认为探寻使高温态稳定存在于室温的方法是探索新的离子导体研究中有效途径之一。 关键词：     

Inelastic light scattering and photoluminescence in the mixed valence systems Eu3O4, Eu3S4 and Sm3S4

The thermally activated valence fluctuations of Eu₃S₄ and Sm₃S₄ have been studied using light scattering and photoluminescence techniques and are compared with measurements on the non-fluctuating compound Eu₃O₄, Eu₃S₄ exhibits an anomalous vibrational mode which is associated with the frequency factor of hopping, ν₂=1.3×10¹³ sec^?1. In Sm₃S₄ electronic Raman scattering is observed within the ⁷F₉ multiplet of the Sm²⁺ ion. An anomalous frequency shift of the5d-4f photoluminescence emission band in Eu₃S₄ is related to the temperature dependent fluctuation rate which passes through the reference time scale of the photoluminescence. Intra-4f photoluminescence has also been observed in Eu₃S₄ and Sm₃S₄.     

Si3N4的晶体化和ZrN/Si3N4纳米多层膜的超硬效应

研究了Si₃N₄层在ZrN/Si₃N₄纳米多层膜中的晶化现象及其对多层膜微结构与力学性能的影响. 一系列不同Si₃N₄层厚度的ZrN/Si₃N₄纳米多层膜通过反应磁控溅射法制备. 利用X射线衍射仪、高分辨透射电子显微镜和微力学探针表征了多层膜的微结构和力学性能. 结果表明，由于受到ZrN调制层晶体结构的模板作用，溅射条件下以非晶态存在的Si₃N₄层在其厚度小于0.9 nm时被强制晶化为NaCl结构的赝晶体，ZrN/Si₃N₄纳米多层膜形成共格外延生长的柱状晶，并相应地产生硬度升高的超硬效应. Si₃N₄随层厚的进一步增加又转变为非晶态，多层膜的共格生长结构因而受到破坏，其硬度也随之降低.     

Crystallization of amorphous Si3N4 and superhardness effect in HfC/Si3N4 nanomultilayers

HfC/Si₃N₄ nanomultilayers with various thicknesses of Si₃N₄ layer have been prepared by reactive magnetron sputtering. Microstructure and mechanical properties of the multilayers have been investigated. The results show that amorphous Si₃N₄ is forced to crystallize and grow coherently with HfC when the Si₃N₄ layer thickness is less than 0.95 nm, correspondingly the multilayers exhibit strong columnar structure and achieve a significantly enhanced hardness with the maximum of 38.2 GPa. Further increasing Si₃N₄ layer thickness leads to the formation of amorphous Si₃N₄, which blocks the coherent growth of multilayer, and thus the hardness of multilayer decreases quickly.     

Jahn-Teller band transition in La3S4 and La3Se4

La₃S₄ and La₃Se₄ undergo a cubic to tetragonal phase transformation at a temperature of 103 and 70 K respectively, the c/a ratio is 0.984 for La₃S₄ and 0.987 for La₃Se₄. In these compounds the conduction electron Fermi energy happens to be close to a band structure anomaly which drives the phase transition. We find some indication, that the anomaly might be of ?-type.     

Non-colinear magnetic structure of U3P4 and U3As4

Neutron diffraction experiments have been performed on single crystal samples of U₃P₄ and U₃As₄. The magnetic ordering is found to be a non-collinear three axial structure in which magnetic moments of U⁴⁺ ions are tilted from the [111] axis by an angle of about twenty degrees within (110) planes.     

X-ray photoelectron spectroscopy of Co3O4, Fe3O4, Mn3O4, and related compounds

The metal 2p region spectra of the mixed valence spinels, Co₃O₄, Fe₃O₄, Mn₃O₄, and related compounds were studied. The satellite splittings of Co 2p_{$\text{3}\text{2}$} for the octahedrally coordinated cobaltous ions are 6.2 eV and those for the tetrahedrally coordinated ones are about 5.3 eV. The Co 2p spectrum for Co₃O₄ is considered to be the sum of spectra of magnetic cobaltous ions and low-spin cobaltic ions. In the cases of Fe₃O₄ and Mn₃O₄, the oxidation states were not clearly distinguished because both the divalent and trivalent ions of iron and manganese are high-spin.     

Oscillator strengths for 3dn4s → 3dn4p transitions in the iron series

The observed oscillator strengths for the 3dⁿ4s → 3dⁿ4p transitions in the iron series show anomalous behaviour for Cr and Mn : the former is exceedingly small whereas the latter is unusually large.Theoretical Hartree-Fock gf-values are reported and a considerable discrepancy with experimental values is noted for Cr. The effect of the interaction of 3dⁿ4p with 3d^n?14s4p is studied using a fixed core, multi-configuration Hartree-Fock approximation. This interaction does not improve significantly the agreement with observed values.     

Raman study of NH4NO3 and ND4NO3—250–420K

Raman spectra of NH₄NO₃, and ND₄NO₃, were studied from 250 to 420K. The results show that there are four phases separated by first order transitions. No evidence of the previously reported phase II' was observed.The present results combined with the results of other experiments present the following picture of the state of order of the molecules.In phase I, the highest temperature phase, the NH₄⁺ groups are in a free rotation and the nitrate groups are likely in random reorientation among 12-equivalent positions. In phase II, the NH₄⁺ groups are likely in rapid random reorientation under the local force field of S₄ symmetry. The nitrate groups are in hindered rotation but are disordered with one of the O-N bonds directed in one sense or the other along the c-axis. In phase III, the absence of the librational mode indicates that the NH₄⁺ groups are in nearly free rotation but the rotational motion is restricted by the local force field of C₃ symmetry. The nitrate groups are probably ordered as suggested by the well polarized character of the modes associated with the nitrate groups. In phase IV, the nitrate groups are ordered with their molecular planes perpendicular to the b-axis. The NH₄⁺ groups are in orientational disorder but may undergo bindered rotations. An optical mode was observed to couple to an anomalous mode which is believed to be a zone edge acoustical mode.     

Magnetic field aligned orderly arrangement of Fe_3O_4 nanoparticles in CS/PVA/Fe_3O_4 membranes

The CS/PVA/Fe_3O_4 nanocomposite membranes with chainlike arrangement of Fe_3O_4 nanoparticles are prepared by a magnetic-field-assisted solution casting method. The aim of this work is to investigate the relationship between the microstructure of the magnetic anisotropic CS/PVA/Fe_3O_4 membrane and the evolved macroscopic physicochemical property. With the same doping content, the relative crystallinity of CS/PVA/Fe_3O_4-M is lower than that of CS/PVA/Fe_3O_4.The Fourier transform infrared spectroscopy(FT-TR) measurements indicate that there is no chemical bonding between polymer molecule and Fe_3O_4 nanoparticle. The Fe_3O_4 nanoparticles in CS/PVA/Fe_3O_4 and CS/PVA/Fe_3O_4-M are wrapped by the chains of CS/PVA, which is also confirmed by scanning electron microscopy(SEM) and x-ray diffraction(XRD)analysis. The saturation magnetization value of CS/PVA/Fe_3O_4-M obviously increases compared with that of non-magnetic aligned membrane, meanwhile the transmittance decreases in the UV-visible region. The o-Ps lifetime distribution provides information about the free-volume nanoholes present in the amorphous region. It is suggested that the microstructure of CS/PVA/Fe_3O_4 membrane can be modified in its curing process under a magnetic field, which could affect the magnetic properties and the transmittance of nanocomposite membrane. In brief, a full understanding of the relationship between the microstructure and the macroscopic property of CS/PVA/Fe_3O_4 nanocomposite plays a vital role in exploring and designing the novel multifunctional materials.