Magnetic properties and magnetocaloric effects in Tb6Co1.67Si3 compound

Magnetic properties and magnetocaloric effects of Tb₆Co_1.67Si₃ have been investigated by magnetization measurement. This compound is of a hexagonal Ce$_{6}$Ni$_{2}$Si$_{3}$-type structure with a saturation magnetization of 187\,emu/g at 5\,K and a reversible second-order magnetic transition at Curie temperature $T_{\rm C} = 186$\,K. A magnetic entropy change $\Delta S = 7$\,J\,$\cdot$\,kg$^{-1}$\,$\cdot$\,K$^{-1}$ is observed for a magnetic field change from 0 to 5\,T. A large value of refrigerant capacity (RC) is found to be 330\,J/kg for fields ranging from 0 to 5\,T. The large RC, the reversible magnetization around $T_{\rm C}$ and the easy fabrication make the Tb₆Co_1.67Si₃ compound a suitable candidate for magnetic refrigerants in a corresponding temperature range.     

High energy electron radiation effect on Ni/4H-SiC SBD and Ohmic contact

The Ni/4H-SiC Schottky barrier diodes (SBDs) and transfer length method (TLM) test patterns of Ni/4H-SiC Ohmic contacts were fabricated, and irradiated with 1~MeV electrons up to a dose of 3.43× 10¹⁴~e/cm^-2. After radiation, the forward currents of the SBDs at 2~V decreased by about 50%, and the reverse currents at -200~V increased by less than 30%. Schottky barrier height (φ _B ) of the Ni/4H-SiC SBD increased from 1.20~eV to 1.21~eV under 0~V irradiation bias, and decreased from 1.25~eV to 1.19~eV under -30~V irradiation bias. The degradation of φ _B could be explained by the variation of interface states of Schottky contacts. The on-state resistance (R_s) and the reverse current increased with the dose, which can be ascribed to the radiation defects in bulk material. The specific contact resistance (\rho_c) of the Ni/SiC Ohmic contact increased from 5.11× 10⁵~Ωega.cm² to 2.97× 10^-4~Ωega.cm².     

The effects of interstitial oxygen on superconducting electronic phases in strontium and oxygen co-doped La1.937Sr0.063CuO4＋δ

Strontium and oxygen co-doped La1.937Sr0.063CuO4＋δ superconductor with Tc≈ 40K, which is obtained by oxidizing strontium-doped starting ceramic sample La1.937Sr0.063CuO4 in NaC10 solution, is annealed under different conditions to allow interstitial oxygen to redistribute. The evolution of the intrinsic superconducting property with the oxygen redistribution is studied in detail by magnetic measurements in various fields. It is found that there occurs the electronic phase separation from the single superconducting phase with Tc ≈ 40 K into two coexisting superconducting states with values of Tc： 15 and 40K or of 15 and 35 K in this system, depending on annealing condition. Our results indicate that the 15, 35 and 40 K superconducting phases associated with the excess oxygen redistribution are all thermodynamically meta-stable intrinsic states in this Sr/O co-doped cuprate.     

Novel material for nonvolatile ovonic unified memory (OUM)－Ag11In12Te26Sb51 phase change semiconductor

In this paper, Ag_{11}In_{12}Te_{26}Sb_{51} phase change semiconductor films have been prepared by dc sputtering. The crystallization behaviour of amorphous Ag_{11}In_{12}Te_{26}Sb_{51} thin films was investigated by using differential scanning calorimetry and x-ray diffraction. It was found that the crystallization temperature is about 483K and the melting temperature is 754.8K and the activation energy for crystallization, E_a, is 2.07eV. The crystalline Ag_{11}In_{12}Te_{26}Sb_{51} films were obtained using initializer. The initialization conditions have a great effect on the sheet resistance of Ag_{11}In_{12}Te_{26}Sb_{51} films. We found that the effect of the initialization condition on the sheet resistance can be ascribed to the crystallinity of Ag_{11}In_{12}Te_{26}Sb_{51} films. The sheet resistance of the amorphous (R_{amo}) film is found to be larger than 1×10^6Ω and that of the crystalline (R_{cry}) film lies in the range from about 10^3 to 10^4Ω. So we have the ratio R_{amo}/R_{cry}=10^2～10^3, which is sufficiently large for application in memory devices.     

Kiselev黑洞的热力学性质和物质吸积特性

本文考虑带有黑洞视界和宇宙视界的Kiselev时空.研究以黑洞视界和宇宙视界为边界的系统的热力学性质.统一地给出了两个系统的热力学第一定律;在黑洞视界半径远小于宇宙视界半径的情况下,近似地计算了通过宇宙视界和黑洞视界的热能.然后,探讨Kiselev时空的物质吸积特性.在吸积能量密度正比于背景能量密度的条件下给出黑洞的吸积率,讨论了黑洞吸积率与暗能量态方程参数的关系.     

Incommensurate-commensurate magnetic phase transition in double tungstate Li2Co(WO4)2

Magnetic susceptibility, specific heat, and neutron powder diffraction measurements have been performed on polycrystalline Li$_{2}$Co(WO$_{4}$)$_{2}$ samples. Under zero magnetic field, two successive magnetic transitions at $T_{\rm N1}\sim 9.4$ K and $T_{\rm N2}\sim 7.4$ K are observed. The magnetic ordering temperatures gradually decrease as the magnetic field increases. Neutron diffraction reveals that Li$_{2}$Co(WO$_{4}$)$_{2}$ enters an incommensurate magnetic state with a temperature dependent $\bm k$ between $T_{\rm N1}$ and $T_{\rm N2}$. The magnetic propagation vector locks-in to a commensurate value $\bm k = (1/2, 1/4, 1/4)$ below $T_{\rm N2}$. The antiferromagnetic structure is refined at 1.7 K with Co$^{2+}$ magnetic moment 2.8(1) $\mu_{\rm B}$, consistent with our first-principles calculations.     

New criterion in predicting glass forming ability of various glass-forming systems

It has been confirmed that glass-forming ability (GFA) of supercooled liquids is related to not only liquid phase stability but also the crystallization resistance. In this paper, it is found that the liquid region interval ($T_{\rm l}-T_{\rm g})$ characterized by the normalized parameter of $T_{\rm g}$/$T_{\rm l}$ could reflect the stability of glass-forming liquids at the equilibrium state, whilst the normalization of supercooled liquid region $\Delta T_{\rm x}$=($T_{\rm x}-T_{\rm g})$, i.e. $\Delta T_{\rm x}$/$T_{\rm x}$ (wherein $T_{\rm l}$ is the liquidus temperature, $T_{\rm g}$ the glass transition temperature, and $T_{\rm x}$ the onset crystallization temperature) could indicate the crystallization resistance during glass formation. Thus, a new parameter, defined as $\xi =T_{\rm g}$/$T_{\rm l}+\Delta T_{\rm x}$/$T_{\rm x}$ is established to predict the GFA of supercooled liquids. In comparison with other commonly used criteria, this parameter demonstrates a better statistical correlation with the GFA for various glass-forming systems including metallic glasses, oxide glasses and cryoprotectants.     

New criterion in predicting glass forming ability of various glass-forming systems

It has been confirmed that glass-forming ability （GFA） of supercooled liquids is related to not only liquid phase stability but also the crystallization resistance. In this paper, it is found that the liquid region interval （T1 - Tg） characterized by the normalized parameter of Tg/T1 could reflect the stability of glass-forming liquids at the equilibrium state, whilst the normalization of supercooled liquid region △Tx=（Tx - Tg）, i.e. △Tx/Tx （wherein T1 is the liquidus temperature, Tg the glass transition temperature, and Tx the onset crystallization temperature） could indicate the crystallization resistance during glass formation. Thus, a new parameter, defined as ζ = Tg/T1＋△Tx/Tx is established to predict the GFA of supercooled liquids. In comparison with other commonly used criteria, this parameter demonstrates a better statistical correlation with the GFA for various glass-forming systems including metallic glasses, oxide glasses and cryoprotectants.     

激光冷却SH~–阴离子的理论研究

本文采用多组态相互作用及Davidson修正方法和全电子基组计算了SH~-阴离子的X~1∑~+,a~3∏和A~1∏态的势能曲线、电偶极矩和跃迁偶极矩.计算的光谱常数与实验值及已有的理论值符合得很好.在计算中考虑了自旋-轨道耦合效应.计算得到a~3∏_1(v'=0)?X~1∑_(0+)~+(v"=0)和A~1∏_1(v'=0)?X~1Σ_(0+)~+(v"=0)跃迁具有高对角分布的弗兰克-康登因子,分别为0.9990和0.9999;计算得到a~3∏_1和A~1∏_1态的自发辐射寿命分别为1.472和0.188 ms.A~1∏_1?X~1∑_(0+)~+跃迁存在中间态a~3∏_(0+)和a~3∏_1,但中间态对激光冷却SH~-阴离子的影响可以忽略.分别利用a~3∏_1(v'=0)? X~1∑_(0+)~+(v"=0)和A~1∏_1(v'=0)? X~1∑_(0+)~+(v"=0)跃迁构建了准闭合的能级系统,冷却所需的激光波长分别为492.27和478.57 nm.最后预测了激光冷却SH~-阴离子能达到的多普勒温度和反冲温度.这些结果为进一步实验提供了理论参数.     

Critical radius and dipole polarizability for a confined system

The analytical transfer matrix method (ATMM) is applied to calculating the critical radius $r_{\rm c}$ and the dipole polarizability $\alpha_{\rm d}$ in two confined systems: the hydrogen atom and the Hulth\'{e}n potential. We find that there exists a linear relation between $r_{\rm c}^{1/2}$ and the quantum number $n_{r}$ for a fixed angular quantum number $l$, moreover, the three bounds of $\alpha_{\rm d}$ ($\alpha_{\rm d}^{K}$, $\alpha_{\rm d}^{B}$, $\alpha_{\rm d}^{U}$) satisfy an inequality: $\alpha_{\rm d}^{K}\leq\alpha_{\rm d}^{B}\leq\alpha_{\rm d}^{U}$. A comparison between the ATMM, the exact numerical analysis, and the variational wavefunctions shows that our method works very well in the systems.     

Magnetic properties and magnetocaloric effect in RE55Co30Al10Si5 (RE = Er and Tm) amorphous ribbons

The magnetic and magnetocaloric effects (MCE) of the amorphous $RE_{55}$Co$_{30}$Al$_{10}$Si$_{5}$ ($RE={\rm Er}$ and Tm) ribbons were systematically investigated in this paper. Compounds with $R ={\rm Er}$ and Tm undergo a second-order magnetic phase transition from ferromagnetic (FM) to paramagnetic (PM) around Curie temperature $T_{\rm C} \sim 9.3$ K and 3 K, respectively. For Er$_{55}$Co$_{30}$Al$_{10}$Si$_{5}$ compound, an obvious magnetic hysteresis and thermal hysteresis were observed at low field below 6 K, possibly due to spin-glass behavior. Under the field change of 0 T-5 T, the maximum values of magnetic entropy change ($-\Delta S_{\rm M}^{\rm max}$) reach as high as 15.6 J/kg$\cdot$K and 15.7 J/kg$\cdot$K for Er$_{55}$Co$_{30}$Al$_{10}$Si$_{5}$ and Tm$_{55}$Co$_{30}$Al$_{10}$Si$_{5}$ compounds, corresponding refrigerant capacity (RC) values are estimated as 303 J/kg and 189 J/kg, respectively. The large MCE makes amorphous $RE_{55}$Co$_{30}$Al$_{10}$Si$_{5 }$ ($RE={\rm Er}$ and Tm) alloys become very attractive magnetic refrigeration materials in the low-temperature region.     

Superconductivity in CuIr2-xAlxTe4 telluride chalcogenides

The relationship between charge-density-wave (CDW) and superconductivity (SC), two vital physical phases in condensed matter physics, has always been the focus of scientists' research over the past decades. Motivated by this research hotspot, we systematically studied the physical properties of the layered telluride chalcogenide superconductors CuIr$_{2-x}$Al$_{x}$Te$_{4}$ ($0 \leqslant x \leqslant 0.2$). Through the resistance and magnetization measurements, we found that the CDW order was destroyed by a small amount of Al doping. Meanwhile, the superconducting transition temperature ($T_{\rm c}$) kept changing with the change of doping amount and rose towards the maximum value of 2.75 K when $x=0.075$. The value of normalized specific heat jump ($\Delta C/\gamma T_{\rm c}$) for the highest $T_{\rm c}$ sample CuIr$_{1.925}$Al$_{0.075}$Te$_{4}$ was 1.53, which was larger than the BCS value of 1.43 and showed the bulk superconducting nature. In order to clearly show the relationship between SC and CDW states, we propose a phase diagram of $T_{\rm c}$ vs. doping content.     

Spin polarization effect for Cr2 molecule

Density functional theory （DFT） （B3P86） of Gaussian 03 has been used to optimize the structure of the Cr2 molecule, a transition metal element molecule. The result shows that the ground state for the Cr2 molecule is a 13- multiple state, indicating that there exists a spin polarization effect in the Cr2 molecule. Meanwhile, we have not found any spin pollution because the wave function of the ground state does not mingle with wave functions of higher-energy states. So the ground state for Cr2 molecule being a 13-multiple state is indicative of spin polarization effect of the Cr2 molecule among transition metal elements, that is, there are 12 parallel spin electrons in the Cr2 molecule. The number of non-conjugated electrons is greatest. These electrons occupy different spatial orbitals so that the energy of the Cr2 molecule is minimized. It can be concluded that the effect of parallel spin in the Cr2 molecule is larger than the effect of the conjugated molecule, which is obviously related to the effect of electron d delocalization. In addition, the Murrell Sorbie potential functions with the parameters for the ground state and other states of the Cr2 molecule are derived. The dissociation energy De for the ground state of the Cr2 molecule is 0.1034eV, equilibrium bond length Re is 0.3396 nm, and vibration frequency we is 73.81cm^-1. Its force constants f2, f3 and f4 are 0.0835, -0.2831 and 0.3535 aJ. nm^-4 respectively. The other spectroscopic data for the ground state of the Cr2 molecule ωeχe, Be and αe are 1.2105, 0.0562 and 7.2938 x 10^-4cm^-1 respectively.     

Low-temperature heat capacities and standard molar enthalpy of formation of 4-（2-aminoethyl）-phenol （C8H11NO）

This paper reports that low-temperature heat capacities of 4-（2-aminoethyl）-phenol （C8H11NO） are measured by a precision automated adiabatic calorimeter over the temperature range from 78 to 400 K. A polynomial equation of heat capacities as a function of the temperature was fitted by the least square method. Based on the fitted polynomial, the smoothed heat capacities and thermodynamic functions of the compound relative to the standard reference temperature 298.15K were calculated and tabulated at the interval of 5K. The energy equivalent, εcalor, of the oxygen-bomb combustion calorimeter has been determined from 0.68g of NIST 39i benzoic acid to be εcalor=（14674.69±17.49）J·K^-1. The constant-volume energy of combustion of the compound at T=298.15 K was measured by a precision oxygen-bomb combustion calorimeter to be ΔcU=-（32374.25±12.93）J·g^-1. The standard molar enthalpy of combustion for the compound was calculated to be ΔcHm = -（4445.47 ± 1.77） kJ·mol^-1 according to the definition of enthalpy of combustion and other thermodynamic principles. Finally, the standard molar enthalpy of formation of the compound was derived to be ΔfHm（C8H11NO, s）=-（274.68 ±2.06） kJ·mol^-1, in accordance with Hess law.     

Mutual recombination in slow Si^＋ ＋ H^- collisions

This paper studies the process of mutual neutralization of Si^＋ and H^- ions in slow collisions within the multichannel Landau-Zener model. All important ionic-covalent couplings in this collision system are included in the collision dynamics. The cross sections for population of specific final states of product Si atom are calculated in the CM energy range 0.05 e∨/u-5 ke∨/u. Both singlet and triplet states are considered. At collision energies below -10 e∨/u, the most populated singlet state is Si（3p4p, ^1S0）, while for energies above -150e∨/u it is the Si（3p, 4p, ^1P1） state. In the case of triplet states, the mixed 3p4p（^3S1 ＋^3P0） states are the most populated in the entire collision energy range investigated. The total cross section exhibits a broad maximum around 200 300e∨/u and for ECM ≤ 10e∨/u it monotonically increases with decreasing the collision energy, reaching a value of 8 × 10^-13 cm^2 at ECM = 0.05 e∨/u. The ion-pair formation process in Si（3p^2 ^3PJ）＋H（1s） collisions has also been considered and its cross section in the considered energy range is very small （smaller than 10^-20 cm^2 in the energy region below 1 ke∨/u）.     

SF_6分子最高占据轨道对称性的判断

量化计算是理论研究分子的重要手段,对于具有高对称群的分子,采用子群计算是常用的方法.分子的电子态或分子轨道等的对称性在子群的表示中会出现重迭,从而不能从子群的结果直接给出电子态或分子轨道对称性的归属.本文以如何判断SF6基态1 A_(1g)的电子组态中最高占据轨道的对称性为例来解决这个问题.针对某些文献中的SF6基态1 A1g的电子组态中,最高占据轨道对称性是T_(1g)却写成T_(2g)的问题,采用Molpro量化计算软件,对SF6基态的平衡结构,进行了HF/6-311G*计算,得到了能量三重简并的最高占据轨道的函数表达式,进而运用O_h群的对称操作作用在三个轨道函数上,得到各操作的矩阵表示,于是得到特征标,最后确定了最高占据轨道为T_(1g)对称性.     

Relativistic calculations on the transition electric dipole moments and radiative lifetimes of the spin-forbidden transitions in the antimony hydride molecule

Calculations on the spectroscopic constants and transition properties of the first three states (${\rm a}^{1}\Delta $, ${\rm b}^{1}\Sigma^{+}$, and X$^{3}\Sigma^-$) of the SbH molecule were performed under the relativistic framework using the exact two-component Hamiltonian (X2C). The potential energy curves in the Franck-Condon region were computed and compared with the previous values. Furthermore, the transition dipole moments for the weak spin-forbidden transitions (${\rm b}0^{+}$-X$_{1}0^{+}$, ${\rm b}0^{+}$-X$_{2}$1, X$_{1}0^{+}$-X$_{2}$1, and X$_{2}$1-${\rm a}$2) were reported. The spontaneous radiative lifetime of the ${\rm b}^{1}\Sigma^{+}$ ($\upsilon '=0$) state was calculated as 163.5 $\pm$ 7.5 μs, which is in reasonable agreement with the latest experimental value of 173 $\pm$ 3 μs. The spontaneous radiative lifetimes of the X$_{2}$1 ($\upsilon '=0$) state and the ${\rm a}$2 ($\upsilon '=0$) state were calculated to be 48.6 s and $\sim 8 $ ms, respectively. Our study is expected to be a benchmark transition property computation for comparison with other theoretical and experimental results. The datasets presented in this paper, including the transition dipole moments, are openly available at https://dx.doi.org/10.11922/sciencedb.j00113.00018.     

Temperature dependence of the quenching of N<Subscript>2</Subscript> (C <Superscript>3</Superscript>Π<Subscript>u</Subscript>) by N<Subscript>2</Subscript> (X) and O<Subscript>2</Subscript> (X)

The temperature dependences of the quenching rate constants of the states N₂ (${\rm C} \ {^{3}{ \rm \Pi }_{u}}${\rm C} \ {^{3}{ \rm \Pi }_{u}} v^′=0,1) by N₂ (X) and of the state N₂ (${\rm C} \ {^{3}{ \rm \Pi }_{u}} \ v^{\prime}=0${\rm C} \ {^{3}{ \rm \Pi }_{u}} \ v^{\prime}=0) by O₂ (X) are studied. Time-resolved light emission from the gas was analyzed in the temperature range from 300 K to 210 K keeping the gas at constant density. In case of quenching by N₂ (X), the quenching rate constant for the vibrational level v^′= 0 increases by (13 ±3)% with gas cooling whereas the quenching rate constant for v^′= 1 decreases by (5.0 ±2.5)% in this temperature range. For quenching by O₂ (X), the quenching rate constant decreases by (3 ±2)% with gas cooling. The temperature variation of the N₂ (C ³Π_u v^′=0) emission intensity for pure nitrogen and dry air are calculated using the obtained quenching rate constants and is compared with the experimental data available in the literature.     

冷却速率对液态金属Cu凝固过程中微观结构演变影响的模拟研究

采用Quantum Sutton-Chen(Q-SC)多体势对液态金属Cu在四个不同冷却速率下的凝固过程进行了分子动力学模拟研究. 通过双体分布函数、键型指数、配位数、均方位移及可视化分析, 结果表明：冷却速率对液态金属Cu的微观结构演变有决定性影响. 当冷却速率为1.0×10¹⁴K/s时得到非晶态结构；当冷速分别为1.0×10¹³K/s，1.0×10¹²K/s和1.3×10¹¹K/s时，系统形成以1421键型为主体的面心立方(fcc)与六角密集(hcp)共存的混合晶体结构；且其结晶温度分别为373K，773K和873K，即冷速越慢，其结晶温度越高，结晶程度也越高；且冷速越慢，1421键型越多，混合晶体中面心立方(fcc)结构所占的比例越高. 同时发现，原子的平均配位数的变化与1551，1441，1661键型的变化密切相关, 反映出体系对称性结构的变化规律与配位数的变化有关. 在可视化分析中，进一步采用中心原子法展现出非晶态与晶体结构的2D截面，及在3D下混合晶体中两个基本原子团分别为面心立方(fcc)与六角密集(hcp)基本原子团的具体结构. 关键词： Q-SC多体势 液态金属Cu 凝固过程 分子动力学模拟