Study of the precipitation behavior of NaCl:Pb and KCl:Pb by optical spectroscopy2

The aggregation and precipitation behavior of lead in NaCl and KCl crystals has been systematically investigated by absorption and luminescence spectroscopy. For NaCl, absorption bands at 265 and 285 nm have been identified which correspond to intermediate stages in the formation of a double band (262–266 nm) associated with PbCl₂ precipitates. The kinetics of growth during ageing as well as the thermal annihilation behavior have been obtained for all bands. The emission spectra for excitation at those absorption bands have also been determined. For KCl, absorption bands at 265 and 280 nm develop during ageing at 160 and 200°C and their growth-rate is markedly enhanced by plastic straining. Their emission spectra involve a main band at $\text{\$}\text{?}$550 nm. In contrast to NaCl, no stage has been found where those absorption bands feed into a final band, which could be associated with PbCl₂ precipitates.     

Resistivity superconducting transition in single-crystalline Cd0.95Ni0.05Sb system consisting of non-superconducting CdSb and NiSb phases

Resistivity superconducting transition has been for the first time found in single crystal of two-component 0.95(CdSb)–0.05(NiSb) system. End members of the system are not superconductors under normal conditions. Insulating behavior in temperature dependence of the electrical resistivity, which is due to hopping conductivity, precedes the transition. The resistivity superconducting transition is rather broad, since at cooling down the electrical resistivity starts to fall at 10.5 K, whereas zero resistivity is reached only at ~2.3 K. Longitudinal magnetic field gradually depresses superconductivity and shifts the superconducting transition to lower temperatures. Under magnetic field above 0.5 T, superconductivity is totally destroyed. Main features observed in the resistivity superconducting transition, including its unusually big width and insulating electrical behavior above the transition, can be related to inhomogeneity of the single crystal studied. According to XRD and SEM examinations, the single crystal consists of major CdSb phase and minor NiSb phase. The NiSb phase forms inhomogeneities in the CdSb matrix. Micro-sized needle-like NiSb crystals and nano-sized Ni_1-xSb_x clusters can be considered as typical inhomogeneities.     

Tuning the magnetocaloric properties of La0.7Ca0.3MnO3 manganites through Ni-doping

The effect of Ni²⁺ doping on the magnetic and magnetocaloric properties of La_0.7Ca_0.3MnO₃ manganites synthesized via the auto-combustion method is reported. The aim of studying Ni²⁺-substituted La_0.7Ca_0.3Mn_1 ? xNi_xO₃ ($x=0,0.02,0.07$, and 0.1) manganites was to explore the possibility of increasing the operating temperature range for the magnetocaloric effect through tuning of the magnetic transition temperature. X-ray diffraction analysis confirmed the phase purity of the synthesized samples. The substitution of Mn³⁺ ions by Ni²⁺ ions in the La_0.7Ca_0.3MnO₃ lattice was also corroborated through this technique. The dependence of the magnetization on the temperature reveals that all the compositions exhibit a well-defined ferromagnetic to paramagnetic transition near the Curie temperature. A systematic decrease in the values of the Curie temperature is clearly observed upon Ni²⁺ doping. Probably the replacement of Mn³⁺ by Ni²⁺ ions in the La_0.7Ca_0.3MnO₃ lattice weakens the Mn³⁺–O–Mn⁴⁺ double exchange interaction, which leads to a decrease in the transition temperature and the magnetic moment in the samples. By using Arrott plots, it was found that the phase transition from ferromagnetic to paramagnetic is second order. The maximum magnetic entropy changes observed for the $x=0,0.02,0.07$, and 0.1 composites was 0.85, 0.77, 0.63, and 0.59 J/kg?K, respectively, under a magnetic field of 1.5 T. In general, it was verified that the magnetic entropy change achieved for La_0.7Ca_0.3Mn_1 ? xNi_xO₃ manganites synthesized via the auto-combustion method is higher than those reported for other manganites with comparable Ni²⁺-doping levels synthesized via standard solid state reaction. The addition of Ni²⁺ increases the value of the relative cooling power as compared to that of the parent compound. The highest value of this parameter (～60 J/kg) is found for a Ni-doping level of 2% around 230 K in a field of 1.5 T.     

Luminescent properties of LiCl-Cu single crystals

The absorption, photoluminescence, x-ray luminescence, and thermoluminescence spectra, and the photoluminescence excitation spectra of LiCl-Cu single crystals with different activator concentration were investigated at temperatures of 79–450°K. The absorption spectrum at room temperature has two bands with maxima at 237 and 259 nm. The absorption coefficient of the 237 nm band is proportional to the copper concentration in the crystal (C_Cu ≤ 7·10^?4 mole %). The photoluminescence and x-ray luminescence spectrum at room temperature consists of one emission band at 324 nm, which conforms with the Mollwo-Ivey rule in the homologous series RbCl → KCl → NaCl → LiCl. The copper ions create trapping levels for electrons and holes at different depths in the forbidden band of the LiCl crystal. The correlation between the thermoluminescence peaks and the recombination-luminescence excitation bands (infrared stimulation) is investigated.     

利用扫描隧道显微镜在溶液中直接观测过渡族金属硫属化合物

本文利用自制的溶液扫描隧道显微镜在溶液环境下直接观测到TiSe₂、MoTe₂和TaS₂样品的原子分辨率图像. 通过将单晶样品在溶液中直接解理,可以保护解理过的新鲜样品表面在几个小时内不会被严重污染. 利用自行搭建的溶液扫描隧道显微镜,首先观察到了TiSe₂活泼样品的原子分辨率图像,并观察到了TiSe₂表面所特有的点缺陷和三角形缺陷结构. 此外,还观察到了MoTe₂的原子分辨率超结构和TaS₂表面的电荷密度波结构. 结果表明：在室温、溶液环境下能更高效的研究过渡族金属硫属化合物等活泼样品的表面电子态结构,同样适用于溶液环境下的电催化和电化学研究.     

Low temperature magneto-resistance,logarithmic resistivity rise and anisotropic superconductivity in TaS2(pyridine)12

The superconducting intercalation complex TaS₂(pyridine)${}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ has received considerable attention as a prototype of two dimensional superconductivity. In this material we have detected a substantial, anisotropic magneto-resistance 11 K° above the superconducting transition and an anisotropic logarithmic resistivity rise below 20°K. The resistively measured superconducting transition temperature is also anisotropic. T_c is the lowest when the current is perpendicular to the layers.     

Thermal and magnetic studies of the nearly one-dimensional antiferromagnetic system CsNiBr3

Magnetic susceptibility, specific heat and ¹³³Cs magnetic resonance measurements in a single crystal of CsNiBr₃ are reported. The data reveal two magnetic transitions separating the paramagnetic phase from the antiferromagnetic ground state. At the higher transition temperature T_N2 = (14.25 ± 0.05)K a net magnetic moment is observed only along the hexagonal c-axis, while only below the lower transition temperature T_N1 = (11.75 ± 0.05)K a perpendicular component of the magnetic moment appears also. Above T_N2 CsNiBr₃ can be described as a one-dimensional antiferromagnet with intrachain exchange interaction $\text{J}\text{k}{}_{\mathrm{B}}\text{= ?(17.0 ± 0.2)}\text{K}$ and single-ion anisotropy constant $\text{D}\text{k}{}_{\mathrm{B}}\text{? ?1.5}\text{K}$. Below T_N1, the data are consistent with the non-colinear triangular structure of the Ni²⁺ moments proposed previously for the isomorphic crystal CsNiCl₃. A reduced value of the zero-temperature susceptibility over the classical value is found and atrributed to the zero point deviations.     

Magnetic and Mössbauer spectroscopic studies of NiZn ferrite nanoparticles synthesized by a combustion method

The properties of nanocrystalline Ni_0.5Zn_0.5Fe₂O₄ synthesized by an auto-combustion method have been investigated by magnetic measurements and Mössbauer spectroscopy. The as-synthesized single phase nanosized ferrite powder is annealed at different temperatures in the range 673–1,273 K to obtain nanoparticles of different sizes. The powders are characterized by powder X-ray diffraction, vibrating sample magnetometer, transmission electron microscopy and Mössbauer spectroscopy. The as-synthesized powder with average particle size of ~9 nm is superparamagnetic. Magnetic transition temperature increases up to 665 K for the nanosized powder as compared to the transition temperature of 548 K for the bulk ferrite. This has been confirmed as due to the abnormal cation distribution, as evidenced from room temperature Mössbauer spectroscopic studies.     

Dependence of superconducting properties of underdoped Bi-2201 single crystals on the charge composition and growth conditions in gas-filled cavities

High-quality Bi_{2 + x} Sr_{2 ? y} CuO_{6 + δ} (Bi-2201) single crystals with the ratio Bi/Sr = 1.4–2.0 were grown by the free growth method in gas-filled cavities in KCl solution-melt in a range of doping levels, which provides variation in superconducting properties from insulators to optimally doped crystals. The charge composition Bi : Sr : Cu = 1.7 : 2.3 : 2.5 with excess Sr and Cu and synthesis conditions provided growth cavity formation in the KCl solution at the crystal growth stage. Lamellar single crystals and whiskers were grown under quasi-equilibrium conditions of lowered growth temperatures and partial oxygen pressure, achieved in closed gas-filled cavities.     

59Co nuclear magnetic resonance in antiferromagnetic CsCoCl3

The ⁵⁹Co NMR in a CsCoCl₃ single crystal has been observed by the spin echo method at 4.2 K. The obtained spectrum is composed of seven distinct lines split by the nuclear-quadrupole interaction. The frequency of the central (± $\text{1}\text{2}$ ? ± $\text{1}\text{2}$) transition 502.08±0.05 MHz corresponds to the hyperfine field of 499.38 ± 0.05 kOe, which agrees well with the calculated value. Due to the interaction of the nucleus with the electronic moment induced by the external field, a shift as large as 18% was observed for the nuclear g-factor.     

A simplified measurement of hydrated crystal densities of low melting points (low transition points) by solidifications of aqueous solutions

A volume change method for measuring crystal densities is described. It allows the densities of unstable hydrated crystals at room temperature to be determined, by measurements of volume changes during the solidification of aqueous solutions. NaCl x 2H2O, KCl, MgSO4 x 12H2O and K2HPO4 x 6H2O were measured by the method and their densities (SE) are 1.61+/-0.02, 1.99+/-0.05, 1.45+/-0.01 and 1.75+/-0.02 g ml(-1) respectively. Data of NaCl x 2H2O and KCl are in good agreement with the previously reported values.     

Growth, thermal and spectroscopic characterizations of BaNd2(MoO4)4 crystal

A new crystal, BaNd₂(MoO₄)₄, has been grown from the flux melt based on Li₂Mo₃O₁₀ by a spontaneous nucleation method. The phase structure of the obtained crystals was determined by X-ray powder diffraction. The result shows that the as-grown crystals are well crystallized and indexed in a monoclinic crystal system with space group B2/b. The specific heat of BaNd₂(MoO₄)₄ crystal at 20 °C is 0.485 J/g K. Absorption and fluorescence spectra were also measured at room temperature. There are several strong and broad absorption peaks from 200 to 1200 nm and three emission transition bands located at 890, 1060, and 1334 nm are detected.     

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.     

A simulation study of rapid solidification and crystal configuration of Cu70Ni30 alloy

A molecular dynamics (MD) simulation study has been performed for the rapid solidification of Cu₇₀Ni₃₀ adopting the quantum Sutton-Chen many-body potentials. By analyzing the bond-types and the relation of atomic average energy versus temperature, it was demonstrated that as cooling rate being 2×10¹² K/s, the Cu₇₀Ni₃₀ formed fcc crystal structures and freezing point was found. In addition, having analyzed the transformation of microstructures and the detail of crystal growth by using atomic trace and visual method, not only could the formation of binary disordered solid solution be showed, but also the solidification of liquid metals and the crystal growth processes could be, further understood.     

A simulation study of rapid solidification and crystal configuration of Cu<Subscript>70</Subscript>Ni<Subscript>30</Subscript> alloy

A molecular dynamics (MD) simulation study has been performed for the rapid solidification of Cu₇₀Ni₃₀ adopting the quantum Sutton-Chen many-body potentials. By analyzing the bond-types and the relation of atomic average energy versus temperature, it was demonstrated that as cooling rate being 2×10¹² K/s, the Cu₇₀Ni₃₀ formed fcc crystal structures and freezing point was found. In addition, having analyzed the transformation of microstructures and the detail of crystal growth by using atomic trace and visual method, not only could the formation of binary disordered solid solution be showed, but also the solidification of liquid metals and the crystal growth processes could be, further understood.     

The effect of a silica support: a density functional theory study of the C–H bond activation of ethane on a nickel oxide cluster

The support effect is an important issue in heterogeneous catalysis. A systematic density functional theory computational study is reported here to better understand the C–H bond activation steps in the reaction between C₂H₆ and a model silica‐supported Ni₃O₃ cluster, as well as that between C₂H₆ and an unsupported Ni₃O₃ cluster. Two mechanisms, namely, a radical mechanism (denoted as mechanism A) and a concerted mechanism (denoted as mechanism B) were examined. Both of these mechanisms contain two steps. For the C–H bond activation taking place via mechanism A, the involvement of the model silica support does not change the most favorable pathway significantly; however, it does result in a modest increase in the reaction barrier and the overall Gibbs energy change. For the C–H bond activation taking place via mechanism B, the involvement of the model silica support leads to an increase in the reaction barrier in the first step. The product of this step has a noticeable difference in the structures for the Ni₃O₃ moiety in the unsupported and model silica‐supported systems. The result of charge analysis shows that there is no noticeable charge transfer between the silica support and Ni₃O₃ when they are in the starting reactants, while there is an electron withdrawal from Ni₃O₃ by the silica support when they are in transition states, intermediates, or products. The results here provide deeper insights into the support effect on the C–H bond activation of lower alkanes on supported transition metal catalysts. Copyright © 2015 John Wiley & Sons, Ltd.     

Growth and luminescent properties of the Ce,Pr doped NaCl single crystals grown by the modified micro-pulling-down method

We have investigated luminescent properties of nondope, Ce and Pr doped NaCl [nondope NaCl, Ce:NaCl, Pr:NaCl] single crystals grown by a modified micro-pulling-down method with a removable chamber system. Nondope, Ce 1% and Pr 1% doped NaCl crystals with a single phase of NaCl structure were obtained and the crystals indicated general crystal quality by the X-ray rocking curve measurement. For the nondope NaCl and Pr:NaCl crystals, the transmittance spectra indicated almost more than 60% in the wavelength from 200 to 800 nm and an absorption of Ce³⁺ ion was observed in the transmittance spectrum of Ce:NaCl crystal. The emission spectrum originated from Ce³⁺ 5d–4f transition appeared around 300 nm in the photoluminescence spectrum and the decay time was 19.7 ns.