Raman scattering investigation of the phase transitions in (NH4)2ZnBr4

Results of Raman spectroscopic studies of (NH₄)₂ZnBr₄ crystal in the spectral range from 20-250 cm^-1 and over a range of temperature from 90K to 440K covering the low temperature ferroelectric and high temperature incommensurate phases are presented. The plots of the integrated areas and peak heights of the strong Raman lines versus temperature show anomalous behaviour near the two phase transitions.     

Calorimetric investigations of overcritical behaviour in (TEA)2CuCl4 crystals

The results of experimental investigation of molar heat capacity of [N(C₂H₅)₄]₂CuCl₄ - ferroelasto-ferroelectric crystals in a wide temperature range are presented. The typical anomaly for the first order phase transition of order-disorder type at 258 K and additional anomaly with maximum at 195 K has been observed. We suggest that the low temperature anomalies of physical properties of [N(C₂H₅)₄]₂CuCl₄ crystals can be attributed to over critical traces of isomorphous phase transitions (similar to that observed in liquid-gas system). Results of numerical analysis of phenomenological model of phase transition in [N(C₂H₅)₄]₂CuCl₄ crystals are presented and compared with the experimentally determined temperature dependence of the specific heat and entropy changes.     

A new low-temperature Tcr=101 K phase transition in (NH4)3H(SeO4)2 evidenced by single crystal ESR

Temperature ESR measurements on SeO₃ - radicals in (NH₄)₃H(SeO₄)₂ single crystals disclosed new ESR anomalies at T = 101 K. Below this temperature the hyperfine splitting becomes to be temperature averaged, ESR linewidth shows motional narrowing and an anomaly in forbidden transition intensity is observed. Also the dielectric measurements show an anomaly of the ε at this temperature. We suggest an existence of a new crystal phase VI below T_cr = 101 K with NH₄-groups ordering and slow SeO₄-group dynamics.     

Solid state protonic conductor NH4PO3–(NH4)2Mn(PO3)4 for intermediate temperature fuel cells

A new proton-conductive composite of NH₄PO₃–(NH₄)₂Mn(PO₃)₄ was synthesized and characterized as a potential electrolyte for intermediate temperature fuel cells that operated around 250 °C. Thermal gravimetric analysis and X-ray diffraction investigation showed that (NH₄)₂Mn(PO₃)₄ was stable as a supporting matrix for NH₄PO₃. The composite conductivity, measured using impedance spectroscopy, improved with increasing the molar ratio of NH₄PO₃ in both dry and wet atmospheres. A conductivity of 7 mS cm⁻¹ was obtained at 250 °C in wet hydrogen. Electromotive forces measured by hydrogen concentration cells showed that the composite was nearly a pure protonic conductor with hydrogen partial pressure in the range of 10²–10⁵ Pa. The proton transference number was determined to be 0.95 at 250 °C for 2NH₄PO₃–(NH₄)₂Mn(PO₃)₄ electrolyte. Fuel cells using 2NH₄PO₃–(NH₄)₂Mn(PO₃)₄ as an electrolyte and the Pt–C catalyst as an electrode were fabricated. Maximum power density of 16.8 mW/cm² was achieved at 250 °C with dry hydrogen and dry oxygen as the fuel and oxidant, respectively. However, the NH₄PO₃–(NH₄)₂Mn(PO₃)₄ electrolyte is not compatible with the Pt–C catalyst, indicating that it is critical to develop new electrode materials for the intermediate temperature fuel cells.     

Phase transitions in R2 SnCl6-type crystals (R = NH3 C2H3, NH3C2H5 and N(CH3)4)

The thermal dilatation in (NH₃ ·CH₃) SnCl₆, (NH₃ · C₂H₅) SnCl₆ and [N(CH₃)] SnCl₆ was measured, and as the results it has turned out that (NH₃ ⁶·C₂H₅) SnCl₆ and [N(CH₃)₄]₂ SnCl₆ undergo the first order transitions at 128 K and 158 K, respectively. The low temperature phases of (NH · C₂H₅) SnCl₆ and [N(CH₃)₄]₂ SnC1₆ are found to be monoclinic and tetragonal, respectively, No phase transition was observed in (NH₃ ·CH₃)₂ SnCl₆ down to 77 K.     

(NH4)2S吸收净化冶炼烟气中SO2回收硫资源的方法

采用(NH₄)₂S溶液吸收净化高浓度SO₂烟气,得到(NH₄)₂S₂O₃和NH₄HSO₃的混合溶液并转移至高压反应釜中,控制反应条件,两种物质发生自氧化还原反应,生成硫磺和(NH₄)₂SO₄.实验考察了吸收SO₂过程和自氧化还原过程的影响条件,结果表明:在pH=3～7,SO₂气体流速300 ml·min^-1,(NH₄)₂S浓度为0.2～1.2 mol·L^-1,常温条件下,烟气中二氧化硫的吸收率达到99.8%以上,且无H₂S生成;在pH=2.5～3.0,温度为130℃条件下,反应进行1 h,硫磺收率达到95%以上,溶液经过蒸发结晶得到(NH₄)₂SO₄.用X射线衍射(XRD)和X射线荧光光谱(XRF)对硫磺和硫酸铵进行表征分析,结果表明:硫磺的纯度为99.14%,硫酸铵中氮元素含量为23.6%.     

Reaction of 4-(naphthylmethyl)bibenzyl, thermally and in the presence of fe ( co )3 ( Pph3 )2

The reaction pathways, kinetics and mechanisms of 4-(naphthylmethyl)bibenzyl (NBBM) have been studied in order to resolve the fundamentals underlying the catalysis of coal liquefaction by Fe-based catalysts. Reactions of NBBM: ( 1 ) under nitrogen in the absence of catalyst, (2) under hydrogen in the absence of catalyst, (3) under nitrogen in the presence of the catalyst precursor Fe(CO)₃(PPh₃)₂, and (4) under hydrogen in the presence of the catalyst precursor Fe(CO)₃(PPh₃)₂ were accomplished. Thermolysis was selective for cleavage of the weak bibenzyl bond, whereas the catalyst precursor effected cleavage at the naphthyl moiety. The catalyst precursor was most effective in the presence of hydrogen, where the rate of consumption of NBBM and the selectivity of breaking the bond at the naphthalene ring both increased. Hydrogenation activity was also observed. Possible mechanisms are proposed to describe the pyrolytic and catalytic reactions of NBBM.     

Scalable synthesis of Na3V2(PO4)3/C with high safety and ultrahigh-rate performance for sodium-ion batteries

NASICON-type Na₃V₂(PO₄)₃ is a promising electrode material for developing advanced sodium-ion batteries. Preparing Na₃V₂(PO₄)₃ with good performance by a cost-effective and large-scale method is significant for industrial applications. In this work, a porous Na₃V₂(PO₄)₃/C cathode material with excellent electrochemical performance is successfully prepared by an agar-gel combined with freeze-drying method. The Na₃V₂(PO₄)₃/C cathode displayed specific capacities of 113.4 mAh·g^-1, 107.0 mAh·g^-1 and 87.1 mAh·g^-1 at 0.1 C, 1 C and 10 C, respectively. For the first time, the 500-mAh soft-packed symmetrical sodium-ion batteries based on Na₃V₂(PO₄)₃/C electrodes are successfully fabricated. The 500-mAh symmetrical batteries exhibit outstanding low temperature performance with a capacity retention of 83% at 0 ℃ owing to the rapid sodium ion migration ability and structural stability of Na₃V₂(PO₄)₃/C. Moreover, the thermal runaway features are revealed by accelerating rate calorimetry (ARC) test for the first time. Thermal stability and safety of the symmetrical batteries are demonstrated to be better than lithium-ion batteries and some reported sodium-ion batteries. Our work makes it clear that the soft-packed symmetrical sodium ion batteries based on Na₃V₂(PO₄)₃/C have a prospect of practical application in high safety requirement fields.     

A raman and infrared spectroscopic study of the ferroelectric phase transition of (CH3NH3)5 Bi2 Br11

The Phase transition of (CH₃NH₃)₅ Bi₂ Br₁₁ from a ferroelectric to a paraelectric state has been followed by infrared and Raman spectroscopy. The libration mode of the (CH₃ NH₃)⁺ cation shows changes in the Raman spectrum probably due to order-disorder processes.     

Unique molecular aggregation of novel naphthalocyanine (near IR absorbing dye)

A series of organic-soluble naphthalocyanine derivatives (Y_mMNcX₄) have been synthesized. Their spectroscopic properties in organic solutions and in thin films were studied. MNcX₄ such as MNc(t-Bu)₄ (5a-5c) and MNc(On-Bu)₄ (5j) formed H-aggregates even in dilute solutions. MNc(CO₂R')₄ (5d-5i) had much stronger H-aggregation properties compared with those ofMNc(t-Bu)₄ and MNc(On-Bu)₄. Especially, MNc(CO₂R')₇ complexes (M=Cu, Pd and Ni) existed exclusively without monomers in the aggregated state even in highly dilute solutions. MNcX₄, which has strong H-aggregation properties, showed merely H- aggregate absorption maxima in thin films. In contrast, Y₂MNcX₄ (4), which has sterically hindered Y groups, showed monomerically pure characteristics in solution. However, thin films of Y₂MNcX₄ have a J-type molecular arrangement, exhibiting a red shift of Q-band absorption. The monomeric properties of Y₂MNcX₄ in solutions and J-type molecular arrangement in thin films arise from steric hindrance of two Y groups, such as R₃SiO-in Y₂MNcX₄, which prevents strong H-aggregation of naphthalocyanine.     

[C16H33N(CH3)3]3[PO4(WO3)4]催化脂肪酸甲酯环氧化性能

在无酸、无溶剂条件下,以[C₁₆H₃₃N(CH₃)₃]₃[PO₄(WO₃)₄]为反应控制相转移催化剂,研究各因素对脂肪酸甲酯(FAME)环氧化反应的影响。结果表明,水相pH对环氧化反应的影响最大,反应适宜pH为4;适宜反应条件为过氧化氢与脂肪酸甲酯中双键摩尔比为1.05:1,反应温度50～60℃,反应时间5 h。在此反应条件下催化剂循环5次不失活,产品环氧值大于4.0%,碘值小于5 g I·(100 g)^-1。并通过元素分析与红外光谱,研究了催化剂在反应过程中的变化,认为磷钨杂多阴离子的分解是导致催化剂失活的关键原因。     

In situ FTIR study on reaction pathways in Ni(CO)4/CH3OK catalytic system for low-temperature methanol synthesis in a liquid medium

An in situ infrared spectroscopic study was conducted to elucidate the reaction pathways for low-temperature methanol synthesis in a catalytic system composed of Ni(CO)₄ and CH₃OK (denoted as Ni(CO)₄/CH₃OK). The reaction was conducted in a liquid medium at 313–333 K with an initial pressure of 3.0 MPa. When CH₃OK was added to Ni(CO)₄ solution at 293 K, different carbonylnickelates, [Ni₅(CO)₁₂]²⁻, [Ni₆(CO)₁₂]²⁻ and [Ni(CO)₃(COOCH₃)]⁻, were immediately formed from Ni(CO)₄. The species and the composition of the carbonylnickel complexes varied with temperature. The variations in concentrations of methanol (MeOH) and methyl formate (MF) during the run, which were determined from their IR absorptions, indicated a pattern characteristic of consecutive reactions with MF as an intermediate. Thus, it was shown that methanol was produced through the carbonylation of MeOH to MF and the subsequent hydrogenation of MF to MeOH. Stable hydridocarbonylnickel anions, [HNi(CO)₃]⁻ and/or [HNi₂(CO)₆]⁻, were observed together with a small amount of Ni(CO)₄ throughout the methanol synthesis. Since Ni(CO)₄ alone showed no activity for the hydrogenation of MF, the hydridocarbonylnickel anions generated in the presence of CH₃OK must be responsible for the reaction. The dual role of CH₃OK in the catalytic system was stated.     

Optical second harmonic study of the ieicommensuirate phase in K2SeO4 and (NH4)2BeF4 crystals

Second harmonic generation was studied in the region of phase transition in K₂SeO₄ and (NH₄)₂BeF₄. Symmetry-forbidden harmonic generation was observed in the incommensurate phases near T_c. The experimental results are explained under assumption that the unipolar domain-like structure with C_2v symmetry appears in the incommensurate phase.     

以溶液法制备的钠掺杂锂离子电池正极材料Li3-xNaxV2(PO4)3/C

以溶液法为制备方法、以葡萄糖为碳源合成了一种钠离子掺杂的锂离子电池正极材料Li_3-xNa_xV₂（PO₄）₃/C（x=0、0.01、0.03、0.05、0.07）。XRD结果显示组成相为单斜晶型,与标准Li₃V₂（PO₄）₃衍射峰完全一致。微量钠掺杂并未改变产物的相组成与晶体结构,但使得晶胞参数有所变化,这种变化有利于提高锂离子的扩散系数。SEM与TEM谱图显示材料颗粒基本为近似椭圆形,粒径分布均匀,碳包覆层完整。充放电测试显示Li_2.97Na_0.03V₂（PO₄）₃/C试样的倍率性能最好,在12C倍率下放电比容量约为100mAh/g,循环伏安测试也证明该试样的锂离子扩散系数较高,比纯相Li₃V₂（PO₄）₃提高了约2个数量级。     

Electrochemical performance of nanocrystalline Li3V2(PO4)3/carbon composite material synthesized by a novel sol–gel method

A novel sol–gel method based on V₂O₅·nH₂O hydro-gel was developed to synthesize nanocrystalline Li₃V₂(PO₄)₃/carbon composite material. In this route, V₂O₅·nH₂O hydro-gel, NH₄H₂PO₄, Li₂CO₃ and high-surface-area carbon were used as starting materials to prepare precursor, and the Li₃V₂(PO₄)₃/carbon was obtained by sintering precursor at 750 °C for 4 h in flowing argon. The sol–gel synthesis ensures homogeneity of the precursors and improved reactivity. The sample was characterized by XRD, SEM and TEM. X-ray diffraction results show Li₃V₂(PO₄)₃ sample is monoclinic structure with the space group of P2₁/n. The TEM image indicates that the Li₃V₂(PO₄)₃ particles modified by conductive carbon are about 70 nm in diameter. The Li₃V₂(PO₄)₃/carbon system showed that the discharge capacities in the first and 50th cycle are about 155.3 and 143.6 mAh/g, respectively, in the range of 3.0–4.8 V. The sol–gel method is fit for the preparation of Li₃V₂(PO₄)₃/carbon composite material which may offer some favorable properties for commercial application.     

溶液法制备铜锌锡硫硒薄膜太阳能电池的研究进展

溶液法因其具有操作流程简单、材料利用率高以及成本低廉等潜在优势,被认为是一种很有发展前景和应用潜力的铜锌锡硫硒(Cu₂ZnSn(S,Se)₄,CZTSSe)薄膜太阳能电池制备方法。本工作将溶液法的研究现状按喷雾热解法、基于浴的水溶液法、纳米粒子溶液法和直接溶液涂膜法进行分类介绍。通过分析和比较各种方法报道过的优化途径(如优化阳离子比例、烧结条件和硒化条件,以及掺入Na、Ge等金属元素),对溶液法制备的高性能Cu₂ZnSn(S,Se)₄薄膜太阳能电池的当前研究成果进行综述,并总结了各种溶液法制备铜锌锡硫硒薄膜电池的优势和所存在的问题。展望其未来的发展,认为今后的研究重点应侧重于薄膜组成和反应途径,以寻求降低Cu₂ZnSn(S,Se)₄吸收层的本征缺陷的方法。     

Crystal chemistry of calcium silicates: Germinate and chromate analogues of KF·2[Ca6(SO4)(SiO4)2O]

The germanate KF·2[Ca₆(SO₄) (GeO₄)₂O] was synthesized by solid state reactions; comparison of the observed and calculated powder pattern, assuming an isostructural relationship with the silicate phase, gives good agreement. Sulphate groups may also be substituted by CrO₄²⁻ to give the isostructural KF·2[Ca₆(CrO₄)(SiO₄)₂O].     

Uniaxial stress dependence of the elastic wave propagation near normal—incommensurate phase transition in (NH4)2ZnCl4

The effect of uniaxial σ₂ stress on the velocity and attenuation of longitudinal ultrasonic wave propagating along the [001] direction in an NH₄)₂ZnCl₄ crystal was studied in the vicinity of the orthorhombic — incommensurate phase transition. A stress induced shift of the transition temperature is dT₁/dσ₂= 0.2 K/MPa. Application of stress greater that 5 MPa results in the appearance of additional anomalies of velocity and attenuation, which are interpreted as manifestations of a new phase induced by uniaxial Stress.     

Electric field effect on 14N NQR and piezoelectric resonance in (CH2)6N4 powder

The electric field effect on ¹⁴N NQR and piezoelectric resonance have been investigated in hexamethylene tetramine [(CH₂)₆ N₄]₁₄ powder. Under the applied dc electric field, only the line broadening of ¹⁴N NQR was observed without any line shift. The line width turns out to be increased with the electric field (E) at the rate of 10.9 ± 2.5 Hz cm/kV, which is in good agreement with the previous report. In addition to the NQR signal, the piezoelectric resonance signal was observed, and its frequency was found to be increased proportionally to E². The experimental result is discussed in terms of the electrostriction of [(CH₂)₆ N₄] material.     

Dielectric dispersion in [N(C2H5)4]2ZnCl4 single crystal

Temperature dependence of the complex dielectric permittivity of [N(C₂H₅)₄]₂ZnCl₄ crystal was measured in the frequency range 300 Hz / MHz. Jump-wise changes in the real and imaginary components of ε* were observed for the three crystallographic directions at the phase transition temperature. The dielectric dispersion clearly apparent in the high-temperature phase, rapidly disappears at the phase transition. The anomalous changes in the dielectric permittivity are related to vibrations of the tetraethylammonium ion. The activation energy of these vibrations amounts to 40 kJ/mol.