Conductivity and dielectric properties of the monomer and polymer of the bis(p-toluene sulfonate) of 2,4-hexadiyne-1,6-diol

The electrical conductivity of single crystals of the bis(p-toluene sulfonate) of 2,4-hexadiyne-1,6-diol (TS) and its polymer (PTS) was measured in a temperature range 77–373 K (to 353 K for TS), dielectric properties were measured from 123 to 283 K. Anomalies of the conductivity and the real part of the complex dielectric permittivity of TS and PTS along the molecular stacking direction at the temperature corresponding to the low-temperature phase transitions were observed. The dependence of phase transitions on the polymerization conversion of the monomer TS was examined. The phase diagram of the TS-PTS mixed system was constructed.     

具有共轭主链聚合物单晶的低温电导测定

用自行组装的低温电导测定装置对77～373K温度范围内双(对甲苯磺酸)-2,4-己二炔-1,6-二醇酯(TS)及其聚合物PTS单晶体的暗电导进行了测定。在c方向上相应于它们低温相转变的温度,TS和PTS的电导均出现异常,此时TS的相变温度是163K和208K。     

TS单晶体及其聚合物PTS的介电和动态力学行为

<正> 聚丁二炔类宏观单晶体以其极大的尺寸,完整性和立体规整的共轭主链,为我们提供了一个准一维体系模型化合物。它们的电性能,非线性光学性能及形成聚合LB膜的能力等具有潜在的应用前景,近年来研究工作非常活跃。丁二炔类化合物中最能培养咸大晶体,从而研究得最多的是双(对甲苯磺酸)-2,4-己二炔-1,6-二醇酯(TS)及其聚合物PTS。我们先后测量过它们的热电势率、电导、膨胀系数、介电性能、光声效     

Pressure dependence of phase transitions in two diacetylene crystals

The phase transitions which occur in a diacetylene polymer crystal (PTS) at 195 K and a diacetylene monomer crystal (DCH) at 142 K have been studied as a function of pressure. For the second-order phase transition in PTS the pressure dependence of the transition temperature was found to be less than 0.05 K MPa^?1; for the first-order transition in DCH it was 0.63 ± 0.08 K MPa^?1.     

TS和PTS单晶体的热刺激电流

测定了双(对甲基磺酸)2,4-己二炔-1,6-二醇酯(TS)及其不同聚合程度TS-PTS混合体和完全聚合的聚合物PTS在100-300K温度范围内的热刺激电流。在沿分子堆砌方向上(对PTS则是大分子链方向)上观察到了它们的热刺激电流,并在相应于它们相变152K和192K处呈现热刺激电流峰。研究了聚合程度对相变的影响,绘制了TS-PTS体系的相图。对另三个热刺激电流峰的归属作了定性解释。     

石蜡/膨胀石墨/石墨烯复合相变储热材料的制备及性能

以石蜡(PA)作为相变储热材料、 膨胀石墨(EG)作为主导热材料和支撑材料, 石墨烯气凝胶(GA)作为导热增强材料和辅支撑材料制备了PA/EG/GA复合相变材料, 研究了GA添加量对复合相变材料相变温度、 相变潜热、 导热性能以及循环稳定性的影响. 结果表明, 所制备的80%PA-17%EG-3%GA复合相变材料导热性能良好, 循环稳定性出色. 与80%PA-20%EG复合材料相比, 该材料的相变温度、 相变潜热以及循环稳定性无明显变化, 但导热系数由4.089 W/(m·K)提升到了5.336 W/(m·K), 显示出良好的应用前景.     

Synthesis and characterization of polyesters derived from succinic acid, ethylene glycol and 1,3-propanediol

Poly(ethylene succinate) (PES), poly(trimethylene succinate) (PTS) and their copolyesters with various compositions were synthesized through a direct polycondensation reaction with titanium tetraisopropoxide as the catalyst. The results of intrinsic viscosity and GPC have proven successful in preparing high molecular weight polyesters. The compositions and the sequence distributions of the copolyesters were determined by analyses of ¹H NMR and ¹³C NMR spectra. The sequence distributions of ethylene succinate units and trimethylene succinate (TS) units were found to be random. Their thermal properties were characterized using differential scanning calorimeter and thermal gravimetric analyzer. All of the copolymers exhibit a single glass transition temperature (T_g). There is no significant difference in the thermal stability among these polyesters. Wide angle X-ray diffractograms (WAXD) were obtained for polyesters which can be crystallized isothermally. The results of thermal analysis and the WAXD patterns indicate that the incorporation of TS units into PES significantly inhibits the crystallization behavior of PES. Additionally, the crystal pattern of PTS is quite different from that of PES. Dynamic mechanical properties of moldable polyesters were investigated using a Rheometer operated at 1 Hz. Below T_g, the incorporation of TS units into PES results in the decline of storage modulus. Above T_g, the effect of crystallinity on the storage modulus can be found.     

Alkyl group as entropy reservoir in an MMX chain complex, Pt2(n-PenCS2)4I

Heat capacity of halogen-bridged one-dimensional binuclear metal complex (so-called MMX chain) having four n-pentyl groups, Pt2(n-PenCS2)4I, was measured by adiabatic calorimetry. A first-order phase transition was observed at 207.4 K when measurement was made after cooling from room temperature. The enthalpy and entropy of transition were determined to be 10.19 kJ mol(-1) and 49.1 J K(-1) mol(-1), respectively. A monotropic phase transition was observed at 324 K on heating, and the entropy of transition was essentially null. The sample once heated above 324 K never returned to the initial phase at room temperature and underwent a higher-order phase transition at 173 K and a first-order phase transition at 220.5 K. The enthalpy and entropy of the first-order phase transition were estimated to be 11.6 kJ mol(-1) and 52.4 J K(-1) mol(-1), respectively. The magnitude of the entropy gain at the phase transition from the initial room-temperature phase to the high-temperature phase at 324 K shows that in Pt2(n-PenCS2)4I a large amount of entropy reserved in alkyl chain is transferred to dithiocarboxylato groups upon the phase transition, as in the cases of Pt2(n-PrCS2)4I and Pt2(n-BuCS2)4I.     

Phase diagram of the TbBr(3)-RbBr binary system: thermodynamic and transport properties of the Rb(3)TbBr(6) compound

Phase equilibria in the TbBr3-RbBr binary system were established from differential scanning calorimetry (DSC) measurements. This binary system is characterized by two compounds, namely Rb3TbBr6 and RbTb2Br7, and two eutectics located at the TbBr3 mole fractions, x = 0.117 (728 K) and x = 0.449 (718 K), respectively. Rb3TbBr6 undergoes a solid-solid phase transition at 728 K and melts congruently at 1047 K with the related enthalpies 7.8 and 58.7 kJ mol(-1), respectively. RbTb2Br7 melts incongruently at 803 K. It undergoes also a solid-solid phase transition at 712 K, a temperature very close to that (718 K) of the second eutectic, and much attention was paid in evidencing and separating these transition and eutectic effects. Separate investigations of the thermodynamic and transport properties were performed on the Rb3TbBr6 compound. These heat capacity and electrical conductivity experimental results suggest an order-disorder mechanism in the alkali-metal cation sublattice whereas the TbBr6 octahedra, forming the anionic sublattice, retain their normal lattice positions.     

A new type of antiferrodistortive structure in a double perovskite with Pb

We have found a new structural transition in Pb(2)MnReO(6) at 410 K. Above this temperature, Pb(2)MnReO(6) is cubic with disordered and dynamic atomic displacements manifested in the large thermal parameters of Pb and O atoms. Below 410 K, the antiferrodistortive shift of 2/3 of Pb(2+) cations away from the high-symmetry cubic site produces a new type of monoclinic cell. The unit cell expands at the transition and the heat capacity shows a peak with thermal hysteresis. These features agree with a first order transition. The entropy content of the transition is quite low indicating that the structural disorder has not been completely removed in the low temperature phase. The monoclinic phase of Pb(2)MnReO(6) shows thermally activated conductivity which does not vary when an external magnetic field is applied. A change in the slope of the resistivity curve, observed at the structural phase transition temperature, is related to a slight difference in the activation energy between both phases. It suggests that the condensation of the distortions likely affects the conduction mechanism. The isothermal magnetization measurements reveal the presence of ferromagnetic contributions below 85 K. The ac magnetic susceptibility shows a dynamic peak at 50 K and, in addition, zero-field-cooled and field-cooled magnetization curves diverge strongly below 80 K. These features might be signature of magnetic inhomogeneity. Magnetic loops, obtained at 5 K, do not show saturation in fields up to 9 T. Furthermore, the measured coercivity increases sharply at low temperature indicating an abrupt change in the magnetic anisotropy. We show that all these magnetic properties point out to a ferrimagnetic ordering of Mn and Re atoms in an intermediate valence state.     

Crystallographic and Magnetic Phase Transitions in the Layered Ruthenium Oxyarsenides TbRuAsO and DyRuAsO

The crystallographic and physical properties of TbRuAsO and DyRuAsO at and below room temperature are reported, including full structure refinements from powder X-ray diffraction data and measured electrical and thermal transport properties, magnetic susceptibility, and heat capacity. Both compounds are isostructural to LaFeAsO (ZrCuSiAs-type, P4/nmm) at room temperature. However, DyRuAsO undergoes a symmetry-lowering crystallographic phase transition near 25 K, and adopts an orthorhombic structure (Pmmn) below this temperature. This structural distortion is unlike those observed in the analogous Fe compounds. Magnetic phase transitions are observed in both compounds which suggest antiferromagnetic ordering of lanthanide moments occurs near 7.0 K in TbRuAsO and 10.5 K in DyRuAsO. The nature of the structural distortion as well as thermal conductivity and heat capacity behaviors indicate strong coupling between the magnetism and the lattice. The behaviors of both materials show magnetic ordering of small moments on Ru may occur at low temperatures.     

Hydrogen transfer between sulfuric acid and hydroxyl radical in the gas phase: competition among hydrogen atom transfer, proton-coupled electron-transfer, and double proton transfer

In an attempt to assess the potential role of the hydroxyl radical in the atmospheric degradation of sulfuric acid, the hydrogen transfer between H2SO4 and HO* in the gas phase has been investigated by means of DFT and quantum-mechanical electronic-structure calculations, as well as classical transition state theory computations. The first step of the H2SO4 + HO* reaction is the barrierless formation of a prereactive hydrogen-bonded complex (Cr1) lying 8.1 kcal mol(-1) below the sum of the (298 K) enthalpies of the reactants. After forming Cr1, a single hydrogen transfer from H2SO4 to HO* and a degenerate double hydrogen-exchange between H2SO4 and HO* may occur. The single hydrogen transfer, yielding HSO4* and H2O, can take place through three different transition structures, the two lowest energy ones (TS1 and TS2) corresponding to a proton-coupled electron-transfer mechanism, whereas the higher energy one (TS3) is associated with a hydrogen atom transfer mechanism. The double hydrogen-exchange, affording products identical to reactants, takes place through a transition structure (TS4) involving a double proton-transfer mechanism and is predicted to be the dominant pathway. A rate constant of 1.50 x 10(-14) cm(3) molecule(-1) s(-1) at 298 K is obtained for the overall reaction H2SO4 + HO*. The single hydrogen transfer through TS1, TS2, and TS3 contributes to the overall rate constant at 298 K with a 43.4%. It is concluded that the single hydrogen transfer from H2SO4 to HO* yielding HSO4* and H2O might well be a significant sink for gaseous sulfuric acid in the atmosphere.     

Semiconductor-metal transition in Ti3O5

Ti₃O₅ shows a first-order phase transition from the monoclinic structure to the pseudobrookite structure at 448°K, at which temperature a magnetic susceptibility anomaly has been reported earlier in the literature. There is an electrical conductivity discontinuity accompanying the phase transition. Incorporation of Fe stabilizes the high-temperature phase of Ti₃O₅; while with 2% Fe the transition temperature and enthalpy change are lowered, with 5% Fe there is no transition. Mössbauer spectra of 2% Fe-doped Ti₃O₅ are similar below and above the transition temperature and show no evidence for magnetic ordering in the low-temperature phase. These results are compared to the VO₂ transition.     

Thermal decomposition of ethanol. III. A computational study of the kinetics and mechanism for the CH3+C2H5OH reaction

The mechanism for the CH3+C2H5OH reaction has been investigated by the modified Gaussian-2 method based on the geometric parameters of the stationary points optimized at the B3LYP/6-311+G(d,p) level of theory. Five transition states have been identified for the production of CH4+CH3CHOH (TS1), CH4+CH3CH2O (TS2), CH4+CH2CH2OH (TS3), CH3OH+CH3CH2 (TS4), and CH3CH2OCH3+H (TS5) with the corresponding barriers 12.0, 13.2, 16.0, 44.7, and 49.9 kcal/mol, respectively. The predicted rate constants and branching ratios for the three lower-energy H-abstraction reactions were calculated using the conventional and variational transition state theory with quantum-mechanical tunneling corrections for the temperature range 300-3000 K. The predicted total rate constant, kt=8.36 x 10(-76) T(20.00) exp(5258/T) cm3 mol(-1) s(-1) (300-600 K) and 6.10 x 10(-25) T(4.10)exp(-4058/T) cm3 mol(-1) s(-1) (600-3000 K), agrees closely with existing experimental data in the temperature range 403-523 K. Similarly, the predicted rate constants for CH3+CH3CD2OH and CD3+C2H5OD are also in reasonable agreement with available low temperature kinetic data.     

High temperature crystal structures and superionic properties of SrCl2, SrBr2, BaCl2 and BaBr2

The structural properties of the binary alkaline-earth halides SrCl₂, SrBr₂, BaCl₂ and BaBr₂ have been investigated from ambient temperature up to close to their melting points, using the neutron powder diffraction technique. Fluorite-structured SrCl₂ undergoes a gradual transition to a superionic phase at 900–1100 K, characterised by an increasing concentration of anion Frenkel defects. At a temperature of 920(3) K, the tetragonal phase of SrBr₂ undergoes a first-order transition to a cubic fluorite phase. This high temperature phase shows the presence of extensive disorder within the anion sublattice, which differs from that found in superionic SrCl₂. BaCl₂ and BaBr₂ both adopt the cotunnite crystal structure under ambient conditions. BaCl₂ undergoes a first-order structural transition at 917(5) K to a disordered fluorite-structured phase. The relationship between the (disordered) crystal structures and the ionic conductivity behaviour is discussed and the influence of the size of the mobile anion on the superionic behaviour is explored.     

LB技术制备双(对甲苯磺酸)-2,4-己二炔-1,6-二醇酯及其聚合物的沉积薄膜

<正> LB(Langmuir-Blodgett)技术是人为排列分子的一项技术。由LB技术制备的LB膜高度规整又极薄,有望在微电子学(分子电子器件)和集成光学(非线性光学器件)等高技术领域中得到应用。本文利用LB技术制备了端头不具备亲水基团的双(对甲苯磺酸)-2,4-己二炔-1,6-二醇酯(TS)的沉积薄膜,用X-射线衍射研究了TS及其聚合物PTS沉积薄膜的分子排列情况。     

[(18‐Crown‐6)K][Fe(1)Cl(1)4]0.5[Fe(2)Cl(2)4]0.5: A Multifunctional Molecular Switch of Dielectric,Conductivity and Magnetic Properties

Multifunctional materials that exhibit different physical properties in a single phase have potential for use in multifunctional devices. Herein, we reported an organic–inorganic hybrid compound [(18‐crown‐6)K][Fe(1)Cl(1)₄]_0.5[Fe(2)Cl(2)₄]_0.5 ( 1 ) by incorporating KCl and FeCl₃ into a 18‐crown‐6 molecule, which acts as a host of the six O atoms providing a lone pair of electrons to anchor the guest potassium cation, and [FeCl₄]^? as a counterion for charge balance to construct a complex salt. This salt exhibited a one‐step reversible structural transformation giving two separate high and low temperature phases at 373 K, which was confirmed by systematic characterizations including differential scanning calorimetry (DSC) measurements, variable‐temperature structural analyses, and dielectric, impedance, variable‐temperature magnetic susceptibility measurements. Interestingly, the structural transformation was coupled to both hysteretic dielectric phase transition, conductivity switch and magnetic‐phase transition at 373 K. This result gives an idea for designing a new type of phase‐transition materials harboring technologically important magnetic, conductivity and dielectric properties.     

Hysteretic spin crossover between a bisdithiazolyl radical and its hypervalent σ-dimer

The bisdithiazolyl radical 1a is dimorphic, existing in two distinct molecular and crystal modifications. The α-phase crystallizes in the tetragonal space group P4?2(1)m and consists of π-stacked radicals, tightly clustered about 4? points and running parallel to c. The β-phase belongs to the monoclinic space group P2(1)/c and, at ambient temperature and pressure, is composed of π-stacked dimers in which the radicals are linked laterally by hypervalent four-center six-electron S···S-S···S σ-bonds. Variable-temperature magnetic susceptibility χ measurements confirm that α-1a behaves as a Curie-Weiss paramagnet; the low-temperature variations in χ can be modeled in terms of a 1D Heisenberg chain of weakly coupled AFM S = (1)/(2) centers. The dimeric phase β-1a is essentially diamagnetic up to 380 K. Above this temperature there is a sharp hysteretic (T↑= 380 K, T↓ = 375 K) increase in χ and χT. Powder X-ray diffraction analysis of β-1a at 393 K has established that the phase transition corresponds to a dimer-to-radical conversion in which the hypervalent S···S-S···S σ-bond is cleaved. Variable-temperature and -pressure conductivity measurements indicate that α-1a behaves as a Mott insulator, but the ambient-temperature conductivity σ(RT) increases from near 10(-7) S cm(-1) at 0.5 GPa to near 10(-4) S cm(-1) at 5 GPa. The value of σ(RT) for β-1a (near 10(-4) S cm(-1) at 0.5 GPa) initially decreases with pressure as the phase change takes place, but beyond 1.5 GPa this trend reverses, and σ(RT) increases in a manner which parallels the behavior of α-1a. These changes in conductivity of β-1a are interpreted in terms of a pressure-induced dimer-to-radical phase change. High-pressure, ambient-temperature powder diffraction analysis of β-1a confirms such a transition between 0.65 and 0.98 GPa and establishes that the structural change involves rupture of the dimer in a manner akin to that observed at high temperature and ambient pressure. The response of the S···S-S···S σ-bond in β-1a to heat and pressure is compared to that of related dimers possessing S···Se-Se···S σ-bonds.     

Ab initio calculations on the mechanism of the oxidation of the hydroxymethyl radical by molecular oxygen in the gas phase: a significant reaction for environmental science

The mechanism of the gas-phase reaction of *CH2OH+O2 to form CH2O+HO2* was studied theoretically by means of high-level quantum-chemical electronic structure methods (CASSCF and CCSD(T)). The calculations indicate that the oxidation of *CH2OH by O2 is a two-step process that goes through the peroxy radical intermediate *OOCH2OH (1), formed by the barrier-free radical addition of *CH2OH to O2. The concerted elimination of HO2* from 1 is predicted to occur via a five-membered ringlike transition structure of Cs symmetry, TS1, which lies 19.6 kcalmol(-1) below the sum of the energies of the reactants at 0 K. A four-membered ringlike transition structure TS2 of Cs symmetry, which lies 13.9 kcalmol(-1) above the energy of the separated reactants at 0 K, was also found for the concerted HO2* elimination from 1. An analysis of the electronic structures of TS1 and TS2 indicates that both modes of concerted HO2* elimination from 1 are better described as internal proton transfers than as intramolecular free-radical H-atom abstractions. The intramolecular 1,4-H-atom transfer in 1, which yields the alkoxy radical intermediate HOOCH2O*, takes place via a puckered ringlike transition structure TS3 that lies 13.7 kcalmol(-1) above the energy of the reactants at 0 K. In contrast with earlier studies suggesting that a direct H-atom abstraction mechanism might occur at high temperatures, we could not find any transition structure for direct H-atom transfer from the OH group of *CH2OH to the O2. The observed non-Arrhenius behavior of the temperature dependence of the rate constant for the gas-phase oxidation of *CH2OH is ascribed to the combined effect of the initial barrier-free formation of the *OO-CH2OH adduct with a substantial energy release and the existence of a low-barrier and two high-barrier pathways for its decomposition into CH2O and HO2*.     

Multi-temperature synchrotron PXRD and physical properties study of half-Heusler TiCoSb

Phase pure samples of the half-Heusler material TiCoSb were synthesised and investigated. Multi-temperature synchrotron powder X-ray diffraction (PXRD) data measured between 90 and 1000 K in atmospheric air confirm the phase purity, but they also reveal a decomposition reaction starting at around 750 K. This affects the high temperature properties since TiCoSb is semiconducting, whereas CoSb is metallic. Between 90 K and 300 K the linear thermal expansion coefficient is estimated to be 10.5 × 10(-6) K(-1), while it is 8.49 10(-6) K(-1) between 550 K and 1000 K. A fit of a Debye model to the Atomic Displacement Parameters obtained from Rietveld refinement of the PXRD data gives a Debye temperature of 395(4) K. The heat capacity was measured between 2 K and 300 K and a Debye temperature of 375(5) K was obtained from modelling of the data. Coming from low temperatures the electrical resistivity shows a metallic to semiconducting transition at 113 K. A relatively high Seebeck coefficient of ～-250 μV K(-1) was found at 400 K, but the substantial thermal conductivity (～10 W mK(-1) at 400 K) leads to a moderate thermoelectric figure of merit of 0.025 at 400 K.