Raman Shift of RMnO3 （R=La, Pr, Nd, Sm） Manganites

Raman-active phonons in orthorhombic perovskite-like RMnO3 were studied by measuring Raman spectra in various scattering configurations. The experimental Raman line wave numbers and the expected shapes for the phonon modes were compared to those reported for other perovskite-like compounds with the Pnma structure and to the results of lattice dynamical calculations. The observed Raman lines in the spectra of RMnO3 were assigned to definite atomic motions. The remaining spectral weight can be explained by the presence of dynamic John-Teller distortions that lower the symmetry of the cubic perovskite.     

Site preference and thermodynamic properties of R3Ni13-xCoxB2（R=Y,Nd and Sm）

This paper investigates the structural stability of intermetallics R3Ni13-xCoxB2(R=Y,Nd and Sm) with Nd 3 Ni 13 B 2-type structure and the site preferences of the transition element Co by using a series of interatomic pair potentials.The space group remains unchanged upon substitution of Co for Ni in R3Ni13-xCoxB2 and the calculated lattice constants are found to agree with reports in literatures.The calculated cohesive energy curves show that Co atoms substitute for Ni with a strong preference for the 3g sites and the order of site preference is 3g,4h and 6i.Moreover,the total and partial phonon densities of states are first evaluated for the R 3 Ni 13 B 2 compounds with the hexagonal Nd 3 Ni 13 B 2-type structure.     

Fragile-to-Strong Transition in Al-Ni-M （M=La,Pr, Nd） Metallic Glasses

We study the dynamic behavior of marginal metallic glass-forming liquids Al-Ni-M （M=La, Pr, Nd） in terms of liquid fragility in high and low temperature regions. The liquids are extremely fragile above the liquidus temperature T liq, but become rather strong near the glass transition temperature Tg. The strength of the transition is inversely correlated with the fragility index at Tg. This relation is discussed in terms of potential energy landscape.     

First-Principles Study of Geometries,Stabilities and Electronic Properties of Ca2Sin （n=1-11） Clusters

The equilibrium geometries, relative stabilities, and electronic properties of Ca2Sin （n = 1-11） clusters have been systematically investigated by using the density function theory at the 6-311G （d） level The optimized geometries indicate that the most stable isomers have three-dimensional structures for n = 3-11. The electronic properties of Ca2 Sin （n = 1-11） dusters axe obtained through the analysis of the natural charge population, natural electron configuration, vertical ionization potential, and vertical electron affinity. The results show that the charges in corresponding Ca2Sin clusters transfer from the Ca atoms to the Sin host. Based on the obtained lowest-energy geometries, the size dependence of cluster properties, such as averaged binding energies, fragmentation energies, second-order energy differences, HOMO- LUMO gaps and chemical hardness, are deeply discussed.     

Stereodynamics of the O（3P） with H2（D2） （ν=0,j=0） reaction

Quasi-classical trajectory theory is used to study the reaction of O(3 P) with H 2 (D 2) based on the ground 3 A″ potential energy surface (PES).The reaction cross section of the reaction O+H 2 →OH+H is in excellent agreement with the previous result.Vector correlations,product rotational alignment parameters P 2 (j · k) and several polarizeddependent differential cross sections are further calculated for the reaction.The product polarization distribution exhibits different characteristics that can be ascribed to different motion paths on the PES,arising from various collision energies or mass factors.     

Raman Active Phonons in RCoO3 （R=La, Ce, Pr, Nd, Sm, Eu, Gd, and Dy） Perovskites

We examine RCoO3 （R=La, Ce, Pr, Nd, Sin, Eu, Gd, and Dy） perovskites prepared with the solid-state reaction method by Raman spectroscopy, and report the Raman active phonons in the RCoO3 perovskites crystallized in cubic symmetry for RCoO3 （R=La, Ce, Pr and Nd） and orthorhombic symmetry for RCoO3 （R=Sm, Eu, Gd, and Dy）. It is found that the Raman spectra of RCoO3 perovskites are strongly dependent on the ionic radius of the rare earth elements, and the frequency shift of the most intense modes of the orthorhombic samples are correlated with some structural parameters such as Co-O bond distances, ionic radius of the rare earth elements and Jahn-Teller distortion. It is clear that Raman spectroscopy has the advantage of sensitivity to structure distortion and oxygen motion.     

Bulk Modulus and Electronic Band Structure of ZnGa2Xa （X=S,Se）： a First-Principles Study

First-principles local density functional calculations are presented for the compounds ZnGa2X4 （X = S, Se）. We investigate the bulk moduli and electronic band structures in a defect chalcopyrite structure. The lattice constants and internal parameters are optimized. The electronic structures are analysed with the help of total and partial density of states. The relation between the cohesive energy and the unit cell volume is obtained by fully relaxed structures. We derive the bulk modulus of ZnGa2Xa by fitting the Birch-Murnaghan＇s equation of state. The extended Cohen＇s empirical formula agrees well with our ab initio results.     

Geometric,stable and electronic properties of Aun-2Y2（n=3-8） clusters

Employing first-principles methods,based on the density function theory,and using the LANL2DZ basis sets,the ground-state geometric,the stable and the electronic properties of Aun-2Y2 clusters are investigated in this paper.Meanwhile,the differences in property among pure gold clusters,pure yttrium clusters,gold clusters doped with one yttrium atom,and gold clusters doped with two yttrium atoms are studied.We find that when gold clusters are doped by two yttrium atoms,the odd-even oscillatory behaviours of Aun-1Y and Aun disappear.The properties of Aun-2Y2 clusters are close to those of pure yttrium clusters.     

First-Principles Study of Electronic and Optical Properties of Y1-xCaxTiO3 （x=0, 0.25, 0.5, 0.75）

The full potential linearized augmented plane wave （FP-LAPW） method with the generalized gradient approximation （GGA） is applied to study the electronic and optical properties of perovskite-type compounds Y1-xCaxTiO3. The lattice parameters, magnetic moment, band structure, density of states and optical conductivity are obtained. The results show that the Ca ion plays an important role in the electronic properties and optical responses. Moreover, the optical properties including the dielectric function, absorption spectrum, extinction coefficient, energy-loss spectrum and refractive index are also discussed.     

Surface reconstruction on stishovite SiO2,HfO2 and rutile TiO2 （001）

This paper systematically investigates the surface reconstruction processes and patterns on stishovite SiO 2,HfO 2 and rutile TiO 2 (001) by using classical molecular dynamics.It is found that these three surfaces relax instead of reconstruction at 0 K,and have little possibility to reconstruct below 40 K.Above 40 K,surface reconstructions take place as collective atomic motion which can be speeded by higher temperature or compressed strain.Several reconstruction patterns with approximate surface energies are found,and electrostatic potentials on them are also provided in comparison with possible microscopic results.     

金属间化合物RMn2Ge2(R=La,Pr,Nd,Sm,Gd,Tb和Y)中的自发磁相变 及相变时的磁弹性异常

在10—800K的温度范围内用X射线衍射方法测量了RMn₂Ge₂(R=La,Pr ,Nd,Sm,Gd,Tb和Y)的晶格常数与温度的变化关系.在各种类型的自发磁相变观察到晶格常数 的磁弹性异常现象.实验得出,自发磁相变时的磁弹性异常主要由Mn次晶格引起,并且Mn-Mn 交换相互作用能不仅与晶格常数a有关,而且与晶格常数c有关.用Kittle的交换反转模型讨 论了低温时的铁磁—反铁磁一阶相变. 关键词： 稀土金属间化合物 磁相变 磁弹性     

First-principles study of the structural,mechanical and electronic properties of ZnX2O4（X=Al,Cr and Ga）

This paper performs first-principles calculations to study the structural,mechanical and electronic properties of the spinels ZnAl2O4 ,ZnGa2O4 and ZnCr2O4 ,using density functional theory with the plane-wave pseudopotential method. Our calculations are in good agreement with previous theoretical calculations and the available experimental data. The studies in this paper focus on the evolution of the mechanical properties of ZnAl2O4 ,ZnGa2O4 and ZnCr2O4 under hydrostatic pressure. The results show that the cubic phases of ZnAl2O4 ,ZnGa2O4 and ZnCr2O4 become unstable at about 50 GPa,40 GPa and 25 GPa,respectively. From analysis of the band structure of the three compounds at equilibrium volume,it obtains a direct band gap of 4.35 eV for ZnAl2O4 and 0.89 eV for ZnCr2O4 ,while ZnGa2O4 has an indirect band gap of 2.73 eV.     

H2（V=3）+H2（He）碰撞中的转动能量转移

激发态Na₂与H₂碰撞,使H₂（V=3,J=3）得到布居,在H₂和He总气压为800 Pa及温度为700 K的条件下,利用相干反斯托克斯拉曼散射（CARS）光谱技术研究了H₂（3,3）与H₂（He）间转动能量转移过程.改变CARS激光束与激发Na₂的激光之间的延迟时间,测量He不同摩尔配比时H₂（3,J）态CARS谱强度的时间演化,得到H₂（3,3）的总弛豫速率系数分别为k_3,3^H₂=（21士5）×10^-3cm³·s^-1和k_3,3^H_e=（5.6士1.6）×10^-13cm³·s^-1.测量H₂（3,J）各转动态的相对CARS谱强度,由速率方程分析,得到H₂（3,3）+H₂→H₂（3,J）+H₂中,对于J=2,4,转移速率系数分别为（11±4）×10^-13cm³·s^-1和（8.2±3.1）×10^-13cm³·s_<sup>-1.在H₂（3,3）+He→H₂（3,J）+He中,对于J=2,4,转移速率系数分别为（3.1±1.2）×10^-13cm³·s^-1和（2.1士0.7）×10¹³cm³·s^-1.对于H₂（3,3）,单量子弛豫|△J|=1约占该态总弛豫率的90%.     

R2Fe14B(R=Ce,Pr,Gd)磁晶各向异性常数K1,K2随温度的变化

本文在1.5—300K温度范围内测量了R₂Fe₁₄B(R=Ce,Pr,Gd)各向异性常数K₁,K₂和各向异性场H_A随温度的变化。同时用单离子模型计算了Pr³⁺离子对Pr₂Fe₁₄B磁晶各向异性的贡献,得到与实验值半定量符合的结果。 关键词：     

稀土元素La,Nd,Pr和Eu的微波等离子体炬（MPT）发射光谱

应用微波等离子体炬（ＭＰＴ）对稀土元素Ｌａ、Ｎｄ、Ｐｒ和Ｅｕ溶液作了摄谱研究。本文介绍了实验方法，得到合适的摄谱条件和主要结果。     

First-principles study of disordering tendencies in Gd2B2O7（B=Ti,Sn,Zr） compounds

This paper performs the density functional theory calculations to obtain some factors influencing the response of pyrochlores Gd2B2O7(B = Ti,Sn,Zr) to ion irradiation-induced amorphization.The 48f oxygen position parameter x,cohesive energy,bond type and defect-formation energy are discussed.The results show that parameter x can be used to indicate the disordering tendencies within a given pyrochlore family.Bond type,cohesive energy and defect-formation energies can be used to explain some experimental observations,but they are not determined exclusively by radiation "resistance" for a different pyrochlore family.     

Structural and physical properties of undoped and nickel-doped BaFe2-xNixAs2（x = 0,0.04） single crystals

<正>Single crystals of undoped and nickel-doped BaFe_(2-x)Ni_xAs_2(x=0,0.04) have been grown by FeAs self-flux method.The maximum dimension of the crystal is as large as ~ 1 cm along the ab plane.The crystalline topography of a cleaved crystal surface is examined by scanning electron microscope(SEM).By x-ray powder diffraction(XRD) experiments using pure silicon as an internal standard,precise unit cell parameters(tetragonal at room temperature) are determined:a = 3.9606(4) A(1 A=0.1 nm),c = 13.015(2) A for BaFe_(1.96)Ni_(0.04)As_2 and a = 3.9590(5) A,c = 13.024(1) A for BaFe_2As_2.DC magnetization and transport measurements are performed to check superconducting transition(T_c=15 K for x=0.04) and other subtle anomalies.For BaFe_(0.96)Ni_(0.04)As_2 crystal,the resistance curve at normal state shows two distinct anomalies associated with spin and structure transitions,and its magnetization data above ~ 91 K exhibit a linear temperature dependence due to spin density wave(SDW) instability.     

Al2O3X2（X=H,D,T）的电子振动近似方法

用密度泛函理论在B3LYP/6-311++g（d,p）基组水平上对Al₂O₃X₂（X=H,D,T）分子的可能较低能量构型进行了几何优化.结果表明该分子的基态电子态和对称性为Al₂O₃X₂（X=H,D,T）（¹A′）C_s,计算了氢同位素分子及Al₂O₃X₂（X=H,D,T）的电子能量E、定容热容C_V和熵S.用电子振动近似方法计算了固体Al₂O₃的氢化热力学函数△H⁰,△S⁰,△G⁰,以及平衡压力与温度的关系.当Al₂O₃吸附氢（氘,氚）形成固体时,反应的氢氘氚排代效应的顺序为氚排代氘,氘排代氢,与钛等金属与氢及其同位素反应的氢氘氚排代效应的顺序相反.总体来说,这种排代效应都非常弱.随着温度的增加,这系列反应的氢氘氚排代效应趋于消失.     

μSR Investigation of magnetic phases in R1−xSrxCoO3 oxides (R=Pr, Nd)

We report results of our muon spin relaxation measurements in the series of polycrystalline compounds Pr_1−xSr_xCoO₃ (x=0.3, 0.4 and 0.5) and Nd_1−xSr_xCoO₃ (x=0.3 and 0.5). For the Pr-based samples our data clearly indicate the existence of two magnetic transitions, as also inferred from macroscopic measurements. While the high temperature transition is typical for cobaltites (∼200 K), the low temperature one is unusual. In our experiments it occurs below about 120 K and it manifests itself as a change in the slope of the temperature variation of the muon spin depolarization rate λ(T). For the Nd-based samples we found an increase of the muon spin depolarization rate below 45 K, temperature at which the sample is ferrimagnetic, when the Nd sublattice coupled antiparallel to the Co lattice. No phase separation could be evidenced in our samples by μSR experiments.     

Relativistic density functional investigation of UX6（X=F,Cl,Br and I）

The molecular structures and the vibrational frequencies of uranium hexahalides UX 6(X=F,Cl,Br and I) molecules are investigated by using local density approximation(LDA) and generalised gradient approximation(GGA) functions(BP,BLYP and RPBE) in combination with two different relativistic methods(scalar and scalar+spin-orbit relativistic effects).The calculated results show that the differences are trivial between scalar and scalar+spin-orbit relativistic methods.The vibrational frequencies are also compared with existing experimental values,and overall,the RPBE approach gives the smallest error.The bond dissociation energies(BDEs) of UX 6 are computed by using the RPBE function,thereby obtaining exact vibrational frequencies.In addition,the calculated magnitudes of the spin-orbit effect on the BDE of UX 6(X=F,Cl,Br,and I) are found to be approximately-0.3198,-0.3218,-0.3609 and-0.4415 eV,respectively.