（CX3）2Y型分子的内旋转势能函数

研究有Ｍ（≥２）个等价的Ｎ（≥３）重对称内旋转陀螺的分子，将内旋运动方程解耦，应用无波函数微扰理论，导出内旋转能谱解析式，应用所得结果及扭转频率的光谱数据，确定了（ＣＨ３）２Ｏ与（ＣＦ３）２ＣＯ分子的内旋转势能函数。     

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.     

Superconductivity, Seebeck coefficient, and band structure transformation in Y1−x CaxBa2Cu3−x CoxOy (x=0–0.3)

The temperature dependences of the resistivity and of the Seebeck coefficient S is studied in three series of Y_1−x Ca_xBa₂Cu_3−x Co_xO_y samples (x=0–0.3) differing in oxygen content. It was found that the critical temperature decreases for y≈7.0, and S(T=300 K) increases with doping, whereas oxygen deficiency results in a nonmonotonic variation of these quantities with increasing x. The band structure parameters have been determined from an analysis of the S(T) relations using a phenomenological theory of electron transport. It was found that an increase in x results in a gradual increase in band asymmetry, which is caused by calcium-induced creation of additional states in the band responsible for conduction in the normal phase. An analysis has shown that high impurity concentrations in oxygen-deficient Y_1−x Ca_xBa₂Cu_3−x Co_xO_y samples bring about an additional ordering of the structure, which may be caused by formation of a cobalt superlattice. It has also been shown that, in the case of Ca and Co codoping, the dependence of critical temperature on effective conduction-band width coincides with the universal correlation relation observed in the YBa₂Cu₃O_y system with single substitutions in various lattice sites. Fiz. Tverd. Tela (St. Petersburg) 41, 1363–1371 (August 1999)     

Hyperfine interactions in R x Gd1− x Fe3 intermetallics R = Tb,Y

The structural and magnetic properties of rare earth iron intermetallic compounds Tb _x Gd_1?x Fe₃ and Y _x Gd_1?x Fe₃ (x = 0. 0, 0. 1, 0. 2, 0. 4, 0. 5, 0. 6, 0. 8, 1. 0) was studied by X-ray diffraction, the ⁵⁷Fe Mössbauer effect and SQUID measurements. All investigated compounds crystallize in the rhombohedral PuNi3-type of crystal structure. The investigation of magnetic properties of R _x Gd_1?x Fe₃ proved their ferrimagnetic behavior. The Curie temperature of the investigated compounds decreases with the increase of R concentration from 721K (GdFe₃) to 655K (TbFe₃) and 533K (YFe₃). The saturation magnetic moment MS in the R _x Gd _1?x Fe₃ system increase with x parameter. The Mössbauer spectra are analyzed using four sextets, corresponding to three crystallographically (b, c, h) and four magnetically (b, c, h₁, h₂) inequivalent sites for iron. The mean hyperfine magnetic field increases with increase of the Gd concentration     

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.     

Comparative spectroscopic investigation of Yb3x Y3(1 ? x )Al5O12 (x = 3, 5, 10 and 15%) transparent ceramics

Transparent Yb_3x Y_{3(1 ? x} )Al₅O₁₂ (x = 3, 5, 10 and 15%) ceramics were fabricated by solid-state reaction and vacuum sintering method with a mixture of commercial Al₂O₃, Y₂O₃ and Yb₂O₃ powders. Ethanol and 0.5 wt % tetraethoxysilane were doped. Transparent fully dense samples with grain sizes of several micrometers were obtained by sintered at 1750 K. The absorption spectra, emission spectra and fluorescence life time of these transparent Yb_3x Y_{3(1 ? x} )Al₅O₁₂ ceramics at room temperature have been measured and calculated. The air annealed effects of Yb_3x Y_{3(1 ? x} )Al₅O₁₂ ceramics have been compared with un-annealed Yb:YAG transparent ceramics which shows the difference of the Yb³⁺ ions between annealed and unannealed Yb:YAG ceramics is less than 1%.     

Magnetic hyperfine fields in Y2Fe17−x Si x compounds

Y₂Fe_17–x Si _x compounds withx=0, 0.5, 1.0, 1.5, 2.0, 2.5 and3.0 were investigated by magnetic measurement andNMR. It is found that with increasing Si content the Curie temperatureT _C increases while the average Fe magnetic moment _Fe decreases. NMR study indicates that Si preferentially substitute the Fe atoms at 4f sites, which is responsible for the increase ofT _C.     

Pulsed EPR spectroscopy of Gd3+ centers in Ca1−x R x F2+x (R=La, Y) mixed crystals

A study of Gd³⁺ centers in Ca_1?x R _x F_2+x (R=La, Y) crystals using pulsed EPR spectroscopy is presented. The echo-induced EPR (ESE-EPR) spectrum shows, besides the signal of slightly perturbed cubic Gd³⁺ centers, a broad signal at g≈2 due to Gd³⁺ centers at low symmetry sites. To describe the effects of R³⁺ ions on the EPR Gd³⁺, a model, including cubic and linear R³⁺?2F _i ^? centers, is developed. Its predictions are compared with the experimental results. The composition dependence of the EPR signal due to slightly perturbed cubic Gd³⁺ centers in mixed Ca_1?x R _x F_2+x crystals is explained taking into account the different clustering tendency in La and Y crystals. Moreover, the formation of mixed clusters involving R³⁺ and Gd³⁺ ions is proposed for both series of samples. A greater clustering trend is found in the Y crystals than in the La ones. Gd³⁺ ions are found to be a “non innocent” paramagnetic probe for structural studies in these mixed crystals.     

RBa2Cu3O7—x（R=Y,Yb）形成过程的差异及单相YbBa2Cu3O7—x超导体的…

本文通过Ｘ射线衍射（ＸＲＤ）、差热分析（ＤＴＡ）和超导电性测量等手段对ＹＢａ２Ｃｕ３Ｏ７－ｘ（Ｙ－１２３）和ＹｂＢａ２Ｃｕ３Ｏ７－ｘ（Ｙｂ－１２３）相的形成，单相Ｙｂ－１２３超导体的制备，单相Ｙ－１２３超导体的最低形成温度及Ｒ－１２３相的熔点与Ｒ离子半径的关系进行了研究。结果表明Ｙ－１２３和Ｙｂ－１２３相形成过程显著不同，Ｙ－１２３主要通过下一化学反应生成：Ｙ２Ｏ３＋４ＢａＣＯ３＋６ＣｕＯ＋１－２     

ВЛИЯНИЕ СОДЕРЖАНИЯ К ИСЛОРОДА НА ЭЛЕКТРИЧЕСКИЕ И ТЕ РМОЭЛЕКТРИЧЕСКИЕ СВОЙСТВА ТРОЙНОЙ СИС ТЕМЫ Вi2Те3−x Sе x

, Bi₂Te_3–x Se _x . , , . , , . .

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Influence of oxygen content on electric and thermoelectric properties of ternary system Bi₂Te_3–x Se _x

A study is made of the influence of oxygen, contained in the semi-conducting system Bi₂Te_3–x Sé _x , on the electric and thermoelectric properties. It is shown that the addition of oxygen to the prepared samples Bi₂Te_2.4Se_0.6 causes a decrease in electric conductivity while the thermoelectric force remains unchanged. This influence is connected with a decrease in the mobility of the electrons but their concentration is not influenced by the presence of oxygen. Conclusions are reached as to the influence of oxygen on the efficiency of the conversion of thermal energy into electric energy and vice versa.

     

The microregion compositional variation in Y1Ba2Cu3O7−x material

We have investigated the microstructure and compositional distribution of the Y₁Ba₂Cu₃O_7−x superconductor with scanning electron microscopy, energy dispersive X-ray spectrometry and X-ray diffraction. It has been found that the microregion compositions are far from the ideal composition. This is especially due to the yttrium content which is higher than the expected amount in the interfacial region between crystalline grains.     

光谱纯Y2O3,La2O3,Lu2O3中微量杂质的光致发光谱研究

测定了光谱纯稀土化合物Ｙ２Ｏ３，Ｌａ２Ｏ３，Ｌｕ２Ｏ３中微量杂质在４８８．０ｎｍ和５１４．５ｎｍ激光线激发下的光致发光谱以及在可见光４４５～７４１ｎｍ范围内吸收谱，Ｙ２Ｏ３，Ｌｕ２Ｏ３样品在４４８．０ｎｍ和５１４．５ｎｍ激光激发下都有发光效应，而Ｌａ２Ｏ３样品只在４８８．０ｎｍ激光激发下才发光，分析了结果表明，Ｙ２Ｏ３，Ｌａ２Ｏ３，Ｌｕ２Ｏ３的发光谱分别是由其存在的微量Ｅｒ＾３＋，Ｓｍ＾３＋和Ｅｕ     

Structural, thermal, and electrical properties of (100?x) ZrO2 (x) Bi2O3 compound

Composition (100?x) ZrO₂ (x) Bi₂O₃ (x?=?15, 20, 25) is synthesized by solid-state reaction method to study the effect of Bi₂O₃ doping on ZrO₂. The as-prepared samples are characterized by various methods. The X-ray diffraction pattern of all these samples exhibits three phases, namely, m-ZrO₂, ??_III-Bi₂O₃, and ??-Bi₂O₃. The differential thermal analysis curves do not show any phase transition/decomposition, which clearly indicated the stabilization of ??-Bi₂O₃ phase. The conductivity changes in all the samples are discussed in terms of different phase formations and their volume fractions. The microstructural and energy dispersive analyses indicate the presence of different phases. A maximum conductivity at high temperature (800?°C) was observed for the x?=?25 composition, i.e., ???=?4.21?×?10^?2 S/cm.     

Superconductivity and magnetism in Y1−x Ca x Sr2GaCu2O7−δ

Samples of Y_1–x Ca _x Sr₂GaCu₂O_7– (x=0, 0.4) doped with⁵⁷Fe, prepared under various oxygen pressures, have been studied by magnetometry and Mössbauer spectroscopy. Most of the iron ions (Fe³⁺) enter the Ga(Cu(1)) site. For thex=0 sample, the Mössbauer spectra of the iron nuclei in the Cu(2) sublattice display magnetic order of Cu,T _N=370 K. The iron ions in the Ga site display magnetic order only at low temperatures. At temperatures above 90 K, these iron ions display a pure quadrupole doublet Mössbauer spectrum. The samplex=0.4 also displays magnetic order of the Cu(2) site,T _N370 K. A sharp drop in the hyperfine field is observed atT _N, probably associated with a first-order phase transition or two-dimensional ordering. The iron nuclei in the Ga site display paramagnetic long spin relaxation time phenomena at 4.2 K. Thex=0.4 sample prepared under 110 atm oxygen pressure, displays superconductivity,T _c50 K. The Mössbauer spectra give evidence of the presence of two phases. One displays magnetic order, the other is paramagnetic, the last is probably associated with the superconducting phase.     

Magnetic Pair-Breaking in Y1-xHoxNi2B2C （x = 0, 0.25, 0.5, 0.75） Single Crystals

Temperature-dependent resistivity and magnetic susceptibility were studied for quaternary borocarbide intermetallic compounds Y1-xHoxNi2B2C （x = 0, 0.25, 0.5, 0. 75）, which show coexistence of superconductivity with magnetism. In a normal state, the compounds exhibit conventional metallic behaviour. The Debye temperature θD is derived by fitting the temperature dependence of resistivity to the Bloch-Gruneisen expression, i.e. θD scales with M^-0.5 （M is the averaged atomic mass on the Y^3＋ site）, which means that the acoustic mode of the lattice vibrating spectrum is influenced by the Y^3＋ site atoms. Fitting the temperature-dependent magnetic susceptibility above TN to the Curie-Weiss law, effective magnetic moment μeff is deduced, and then de Gennes factor dG is calculated. It is found that as Ho content increases, μeff as well as dG increases and Tc decreases. Moreover, the decrease of Tc scales with dG, i.e., △Te ∝ -nI^2 N （EF ）dG, which is consistent with the prediction of the Abrikosov-Gor＇kov theory. We suggest that pair-breaking effect of magnetic Ho^3＋ ions. The significant impact on To. the depression of Tc could be mainly ascribed to the magnetic change of Debye temperature with Ho content may not have significant impact on Tc.     

Thermal conductivity of single crystals of the Ca1 − x Y x F2 + x solid solution

The thermal conductivity of single crystals of the solid solution of yttrium fluoride in calcium fluoride Ca_{1 ? x} Y _x F_{2 + x} with the fluorite structure (x ≤ 0.20) and the Ca_0.27Y_0.73F_2.73 phase with the tisonite structure has been studied by the absolute steady-state longitudinal heat flow method in the temperature range 50–300 K. It has been established that the thermal conductivity drops sharply with increasing yttrium trifluoride concentration, especially in the low-temperature region.     

Structural,morphologic and optical characterization of In(2−x)Al x S3

Aluminum-doped indium sulfide thin films are deposited on glass by spray pyrolysis technique. The structure and the surface morphology of these films were characterized by X-ray diffraction and atomic force microscopy. The effects of aluminum ratio z and substrate temperature T _s, on the film structure and grain size are discussed. The influence of aluminum ratio on surface morphology is revealed by scanning electron microscope. Besides, energy dispersive spectrometry technique is used to compare atomic aluminum concentration in the film with aluminum ratio z in spray solution. Optical properties are studied by a spectrophotometer in the wavelength range 350–850 nm, at room temperature. Optical transmission and grain size are found to be maximal for z = 1.8 %. Moreover, band-gap energy is found to increase with aluminum ratio.     

Electron paramagnetic resonance of Gd3+ ions in Ca1 − x − y Y x Gd y F2 + x + y crystals

Electron paramagnetic resonance of Ca_{1 ? x ? y} Y _x Gd _y F_{2 + x + y} single crystals has revealed spectra that are not typical of gadolinium-doped CaF₂ crystals. These spectra have a nearly tetragonal symmetry and are most probably caused by Gd³⁺ ions localized in yttrium clusters. Weak spectra of tetragonal Gd³⁺ centers, whose parameters are close to those of a cubic gadolinium center caused by an isolated Gd³⁺ ion, have been also detected. These centers are attributed to isolated Gd³⁺ ions localized near octahedral rare-earth clusters or their associations.     

CH3NO2和CH3ONO结构及互异化反应的理论研究

采用了B3LYP、MP2方法,详细地计算了硝基甲烷(CH3ONO)和亚硝基甲酯(CH3NO2)的稳定结构、能量和振动频率等,并分析了它们的相对稳定性和相互转换的机理.结构优化结果表明,CH3ONO有两种稳定的构象cis和trans,CH3NO2有一种稳定的结构.在B3LYP/6-31G(d,p)方法的基础上,作出了CH3ONO的能量随CH3O-NO单键旋转的变化曲线图,定性地讨论了CH3ONO可能存在的稳定构象以及两种稳定构象之间互异化的机理.研究了CH3NO2与CH3ONO之间互异化的反应机理,计算了该异化反应发生时几何结构的变化以及最小能量途径,确定了该互异化反应实际上是C-N键和C-O键的断裂或形成的一个过程.     

Spin dynamics in Gd x Y1−x Ba2Cu3O6.85 investigated by ESR of Gd spin probes

Electron spin resonance investigations of Gd³⁺ ions in YBa₂Cu₃O_7?δ give distinct indications for an exchange coupling of these paramagnetic ions to the doped charge carriers and allow the corresponding interaction parameters, as well as the mutual Gd-Gd exchange coupling, to be extracted.