Tetrasulphur Tetranitride: Phase Transition and Crystal Structure at Elevated Temperature

Rietveld X‐ray crystal structure investigations on S₄N₄ give evidence for a new orthorhombic high‐temperature phase (Pbcn, a = 883.9(1) pm, b = 875.5(1) pm, c = 725.81(9) pm) very close to the explosion temperature of the solid‐state material. The phase transition can be described using Landau's theory, yielding a critical temperature of 397 K and a critical exponent of 0.50.     

Crystal Structure and Non-Hydrostatic Stress-Induced Phase Transition of Urotropine Under High Pressure

High-pressure behavior of hexamethylenetetramine (urotropine) was studied in situ using angle-dispersive single-crystal synchrotron X-ray diffraction (XRD) and Fourier-transform infrared absorption (FTIR) spectroscopy. Experiments were conducted in various pressure-transmitting media to study the effect of deviatoric stress on phase transformations. Up to 4 GPa significant damping of molecular librations and atomic thermal motion was observed. A first-order phase transition to a tetragonal structure was observed with an onset at approximately 12.5 GPa and characterized by sluggish kinetics and considerable hysteresis upon decompression. However, it occurs only in non-hydrostatic conditions, induced by deviatoric or uniaxial stress in the sample. This behavior finds analogies in similar cubic crystals built of highly symmetric cage-like molecules and may be considered a common feature of such systems. DFT computations were performed to model urotropine equation of state and pressure dependence of vibrational modes. The first successful Hirshfeld atom refinements carried out for high-pressure diffraction data are reported. The refinements yielded more realistic C−H bond lengths than the independent atom model even though the high-pressure diffraction data are incomplete.     

Anisotropy of lattice distortion of [Co(NH3)5NO2]C2O4 at hydrostatic pressures of up to 4.0 GPa

Variation of the lattice parameters of [Co(NH₃)₅NO₂]C₂O₄ as a function of hydrostatic pressure was studied by powder X-ray diffractom etry in diamond anvils. No phase transitions were observed at pressures below 4.0 GPa, but the structure was anisotropically distorted. The maximal compression was observed in the direction perpendicular to the planes of the oxalate ions and NO₂ ligands.     

Phase diagram of the B-B2O3 system at 5 GPa: experimental and theoretical studies

X-ray diffraction with synchrotron radiation has been used to study in situ the chemical interaction of beta-rhombohedral boron with boron (III) oxide and phase relations in the B-B2O3 system at pressures up to 6 GPa in the temperature range from 300 to 2800 K. The B-B2O3 system has been thermodynamically analyzed, and its equilibrium phase diagram at 5 GPa has been constructed. Only one thermodynamically stable boron suboxide, B6O, exists in the system. It forms eutectic equilibria with boron and B2O3.     

制备条件对尖晶石型LiMn2O4的相行为及结构的影响

将LiNO₃和Mn₃O₄按不同物质的量比[x=n(Li):n(Mn)=0.50,0.52,0.54,0.58,0.62,0.70]混合,在空气气氛下,于700℃烧结得样品.实验发现,在0.52≤x≤0.70的范围内,样品均呈现出单相的尖晶石型LiMn₂O₄结构,晶胞参数随着x的增加而减小.将x=0.50的LiNO₃和Mn₃O₄混合物在不同温度(300,400,500,600和700℃)下进行烧结处理.结果表明,于300℃合成得到的样品为尖晶石型LiMn₂O₄,随着烧结温度的升高,晶胞参数增大;当温度大于600℃时出现杂相,可以通过加入过量的Li(即x≥0.52)来加以抑制.实验结果表明,通过控制烧结温度和Li加入量可以得到理想的尖晶石型LiMn₂O₄单相材料.     

Phase Equilibria in the Systems Na+, K+||Cl--H2O and Na+, K+||Cl-, H2PO- 4-H2O at Temperatures of 0-100°C

Binary and ternary parameters of the Pitzer equation and also the thermodynamic potentials of solid phases and the solubility diagrams of ternary aqueous-salt systems Na⁺, K⁺||Cl^--H₂O and Na⁺, K⁺||Cl^-, H₂PO^- ₄-H₂O in the temperature range 0-100°C, which corresponds to the technological conditions of brine formation, were calculated.     

A new EPR dosimeter based on 2:1 mixture of Li2C2O4:Na2C2O4 for gamma and neutron dosimetry

Electron paramagnetic resonance (EPR) investigations of Li₂C₂O₄, Na₂C₂O₄ mixed in proportion 1:0, 0:1, 1:1, 2:1 and 3:1 were carried out to measure the absorbed dose from photons and thermal neutrons in a mixed radiation field. A single line spectrum of CO₂^? radical anion centered around g=2.0045±0.0005 was obtained in the respective cases on gamma and neutron irradiation. Except Na₂C₂O₄, other mixtures had shown increase in line width on neutron irradiation possibly due to relaxation effects. Of all combinations, the 2:1 mixture is the more sensitive material for gamma and thermal neutrons. Intensity of CO₂^? radical signal in 2:1 Li₂C₂O₄:Na₂C₂O₄ mixture was found to be linear from 0.006 to 11 kGy for gamma and 40–1530 kGy for thermal neutron doses. Radical signal was found to be stable over a period of 300 days with marginal fading of less than 1 percent. Experimental results thus obtained suggest 2:1 Li₂C₂O₄:Na₂C₂O₄ mixture as the potential neutron dosimeter for medium and high dose range.     

Phase Diagram of Na2S2O3)+t‐Butanol+Water at Ambient Pressure and Temperature

In the present work, we report the studies concerning liquid‐liquid‐solid equilibria for the ternary system sodium thiosulphate (Na₂S₂O₃)+t‐butanol+water at ambient pressure and at room temperature (303±2 K). The solubility data of Na₂S₂O₃ are reported for solutions in water, t‐butanol and solutions of varying concentrations of t‐butanol in water. The phase diagram for the said system is developed, described and compared with similar systems studied such as Na₂S₂O₃+ethanol+water, K₂CO₃+methanol+water, etc. These results have been explained in terms of structural properties of aqueous t‐butanol solutions and further discussed in terms of the effect of ions to cause phase separation.     

有机-无机杂化材料[Na2(H2O)4]2[γ-Mo8O26·(Gly-Gly)2]·4H2O的合成及晶体结构

多金属氧酸盐因其独特的结构而具有较高的抗肿瘤及抗病毒活性,蛋白质和肽是氨基酸的聚合体,氨基酸侧链官能团能与多金属氧酸盐形成新型配合物.了解氨基酸和肽与多金属氧酸盐的相互作用对于深入研究多金属氧酸盐抗肿瘤及抗病毒机理很有意义.我们曾报道了赖氨酸、丙氨酸及甘氨酸二肽与钼磷酸所形成化合物的晶体结构.     

273 K下Na2CO3-Na2SO4-Na2B4O7-H2O四元体系介稳相平衡的实验研究

采用等温蒸发法研究了四元体系Na2CO3-Na2SO4-Na2B4O7-H2O在273 K时的介稳相平衡及平衡液相的密度. 利用溶解度数据绘制了该四元体系273 K下的相图. 研究结果表明, 该四元体系有异成分复盐2Na2SO4·Na2CO3形成. 相图中有2个共饱点、5条单变量曲线和4个结晶相区. 4个结晶相区分别为盐Na2CO3·10H2O, Na2SO4·10H2O, Na2B4O7·10H2O和2Na2SO4·Na2CO3的结晶区. 复盐2Na2SO4·Na2CO3同时存在于包含Na2CO3-Na2SO4-H2O三元体系的其它四元体系或高元体系中. 在273 K介稳平衡相图中, 碳酸钠以Na2CO3·10H2O形式析出; 硫酸钠以Na2SO4·10H2O的形式析出; 硼酸钠的完整分子式为Na2B4O5(OH)4·8H2O. Na2CO3对Na2B4O7有盐析作用.     

Phase equilibria in the Na,K,Mg,Ca‖SO4,Cl-H2O system at 25°C in the MgSO4 · 5H2O and MgSO4 · 4H2O crystallization region

Phase equilibria in the Na,K,Mg,Ca‖SO₄,Cl-H₂O system at 25°C in the MgSO₄ · 5H₂O and MgSO₄ · 4H₂O crystallization region are studied using the translation method. MgSO₄ · 5H₂O and MgSO₄ · 4H₂O, which are equilibrium phases of the system at 25°C, are each involved in two invariant points, seven monovariant curves, and nine divariant fields. Fragments of the phase equilibria diagram for the title system in the MgSO₄ · 5H₂O and MgSO₄ · 4H₂O crystallization region are constructed.     

Crystal Structure, Phase Transition, and Thermodynamic Properties of Bis-dodecylammonium Tetrachlorozincate (C12H25NH3)2ZnCl4(s)

The crystal structure and composition of (C₁₂H₂₅NH₃)₂ZnCl₄(s) were characterized by chemical and elemental analysis, X‐ray powder diffraction technique and X‐ray crystallography. The lattice energy of the title compound was calculated to be U_POT=888.82 kJ·mol^?1. Low temperature heat capacities of the title compound have been measured by a precision automated adiabatic calorimeter over the temperature range from 80 to 403 K. An obvious solid to solid phase transition occurred in the heat capacity curve, and the peak temperature, molar enthalpy and molar entropy of the phase transition of the compound were determined to be T_trs= (364.02±0.03) K, (_trsH_m= (77.567±0.341) kJ·mol^?1, and (_trsS_m= (213.77±1.17) J·K^?1·mol^?1, respectively. Experimental molar heat capacities before and after the phase transition were respectively fitted to two polynomial equations. The smoothed molar heat capacities and fundamental thermodynamic functions of the sample relative to the standard reference temperature 298.15 K were calculated and tabulated at an interval of 5 K.