Ionic liquid; possibility of protein-preserving solvent under high pressure

We have investigated the pressure-induced phase transition behavior (～3.0 GPa) of aqueous 1-butyl-3-methylimidazolium chloride ([bmim][Cl]) solutions with N-methylacetamide (NMA), which is a simple protein model compound, using Raman spectroscopy. From Raman spectral changes and optical observation in the sequence of elevated pressure, we found that the aqueous [bmim][Cl] solution with NMA in the water-rich condition induces the high pressure crystallization at 2.6 GPa. On the other hand, in the [bmim][Cl]-rich condition, high pressure crystalline phase was not observed even up to 3.0 GPa. Our results show that the aqueous [bmim][Cl] solution in the ionic liquid-rich condition along with the use of pressure has a potential for protein-preserving solvent.     

Composition dependence of polymorphism and electrical conductivity in Ce(IV)-doped Bi4V2O11

For the first time, a new member of the BIMEVOX family, namely BICEVOX, has been synthesized by the partial solid-state substitution of Ce(IV) for vanadium in parent Bi₄V₂O₁₁ solid electrolyte. The electrical conductivity in Bi₄Ce _x V_{2? x} O_{11?( x /2)? δ} has been investigated in the compositional range 0 ≤ x ≤ 0.30, using FT-IR, X-ray powder diffraction, differential thermal analysis and ac impedance spectroscopy. Owing to the long-term stabilization of α- and β-polymorphs compared to other members of the BIMEVOX family, the BICEVOX system may be a prospective solid electrolyte for intermediate temperature solid oxide fuel cells due to the significantly increased conductivity at lower temperatures observed for the compositions x > 0.20.     

Superconducting properties of barium in three phases under high pressure from first principles

Electron-phonon coupling (EPC) in the three high-pressure phases of Ba is investigated using a pseudopotential plane-wave method based on density functional perturbation theory. The calculated values of superconducting critical temperature T c of Ba-I and Ba-II under pressure are consistent well with the trends observed experimentally. Moreover, Ba-V is found to be superconducting with a maximum T c exceeding 7.8 K at 45 GPa. With the increase of pressure, the values of T c increase in Ba I and Ba-II but the value of T c decreases in Ba-V. For Ba-I at pressures below 2 GPa, the increases of logarithmic average frequency ω log and electron-phonon coupling parameters λ both contribute to the enhancement of T c . For all the three phases at pressures above 2 GPa, T c is found to be primarily determined by λ . Further investigation reveals that for all the three phases, the change in λ with pressure can be explained mainly by change in the phonon frequency. Thus for Ba-II and Ba-V, although they exhibit completely different superconducting behaviors, their superconductivities have the same origin; the pressure dependence of T c is determined finally by the pressure dependence of phonon frequency.     

KAg4I5-AgI复合体系的电导率研究

采用固相反应法将市购的AgI和KI按4.1 ∶1的摩尔组分配比,在避光干燥的条件下混合加热,制备出了KAg₄I₅ (10%AgI )复合体系.用X射线衍射谱、扫描电子显微镜、复阻抗谱、差示扫描量热等分析手段,对复合体系的结构、形貌、离子导电特性及相变温度进行了研究.结果发现,两相均为快离子导体的材料复合后,其复合体系的离子电导率比各自为纯相时都高,并且升降温-电导率曲线为迟滞回线,AgI的升降温相变温度分别滞后5和10 ℃.用界面间相互作用、空间电荷模型及Gou 关键词： 离子电导率 电化学势 空间电荷区 相变温度     

Effect of enantiomeric excess on the smectic-C* phases under electric field

A series of enantiomeric mixtures of 4-(1-methylheptyloxycarbonyl) phenol 4'-octyloxybiphenyl-4-carbonate (MHPOBC) is reported to understand the structures and stability conditions of emerging liquid crystal phases. The mesomorphic properties are studied by microscopic observation, electro-optic and dielectric measurements. The electric field–concentration (E–x) phase diagram for each phase at constant temperature is constructed. The complete electric field–temperature (E–T) phase diagrams for several enantiomeric mixtures of the antiferroelectric MHPOBC are established. These phase diagrams show the influence of optical purity on the phase stability and the unwinding threshold.     

固结压强对纳米PbF2的相变和离子电导率的影响

 用惰性气体蒸发-真空原位固结法制备了直径为10 mm、厚度为1～2 mm的具有清洁界面的纳米PbF₂块体材料,原位固结压强为0.3～1.8 GPa。采用X射线衍射和复阻抗谱方法,研究了固结压强对纳米PbF₂物相组成、晶粒度和离子电导率的影响。结果表明,相同压强下,纳米β-PbF₂比粗晶β-PbF₂更易于向α-PbF₂转化;随着压强增大,样品中低电导率的α-PbF₂相不断增加,导致离子电导率下降。压强引起的连续相变使晶粒度缓慢长大。由于晶粒细小,纳米α-PbF₂的离子电导率比粗晶α-PbF₂提高约一个数量级,与粗晶β-PbF₂相当。     

A study on the electrical property of HgSe under high pressure

Using a microcircuit fabricated on a diamond anvil cell, we have measured in-situ conductivity of HgSe under high pressures, and investigated the temperature dependence of conductivity under several different pressures. The result shows that HgSe has a pressure-induced transition sequence from a semimetal to a semiconductor to a metal, similar to that in HgTe. Several discontinuous changes in conductivity are observed at around 1.5, 17, 29 and 49GPa, corresponding to the phase transitions from zinc-blende to cinnabar to rocksalt to orthorhombic to an unknown structure, respectively. In comparison with HgTe, it is speculated that the unknown structure may be a distorted CsCl structure. For the cinnabar-HgSe, the energy gap as a function of pressure is obtained according to the temperature dependence of conductivity. The plot of the temperature dependence of conductivity indicates that the unknown structure of HgSe has an electrical property of a conductor.     

Nonmetal-metal transitions in liquid substances under high pressure

Abstract

In the melts of Te, Se, S, I₂ and Mg₃Bi₂ the nonmetal-metal transitions were found under pressure. The transitions are accompanied by a decrease of the volume. The transitions seem to terminate at high temperature by “critical regions”. For S and Se the kinetics of the transitions and the pressure influence on the solidification of the melts were investigated.

The existence of the transitions of this kind gives an explanation of anomalies of melting curves of some substances.     

Influence of calcium substitution on the phase transition and ionic conductivity in BICAVOX oxide ion conductor

Samples of Bi₄Ca _x V_{2? x} O_{11?(3 x /2)?δ} in the composition range 0.07 ≤ x ≤ 0.30 were prepared by conventional solid state reactions. The stability of different phases as a function of composition was analysed by X-ray powder diffraction, FT-IR spectra, differential thermal analysis and AC impedance spectroscopy. For the compositions x ≤ 0.10, monoclinic α-phase structure is retained at room temperature. For x = 0.13, orthorhombic β-phase is observed, whereas for x ≥ 0.17, high O^2?conducting tetragonal γ-phase is stabilised. However, the highest ionic conductivity σ_300°C = 3.27 × 10^?4 S cm^?1 was observed for x = 0.17. This higher value of conductivity of the substituted compound as compared to the parent compound can be attributed to the increased oxygen ion vacancies generated as a result of cation doping. AC impedance spectroscopy reveals the fact that this ionic conductivity is mainly due to the grain contribution.     

In situ solidification of ionic liquid [EMIM][EtOSO3] from melt under high pressure

In situ solidification of 1-ethyl-3-methylimidazolium ethyl sulfate [EMIM][EtOSO₃] from melt under high pressure has been investigated by using Raman spectroscopy. The results indicate that [EMIM][EtOSO₃] might experience a phase transition at about 2.4 GPa upon compression, which could be identified as solidification to a superpressurized glass by pressure broadening of the sharp ruby R₁ fluorescence line. Upon cooling, it solidifies as a glassy state rather than crystallizes at low temperature down to 93 K. These facts are suggestive of a phase transition of liquid to a superpressurized glass induced by compression in [EMIM][EtOSO₃], which is similar to the glassy state at low temperature.     

Correlation between phase structure and electrical conduction in BISNVOX system for intermediate temperature solid oxide fuel cells (IT-SOFC)

Samples of Sn⁴⁺-substituted bismuth vanadate, formulated as Bi₄Sn _x V_{2? x} O_{11?( x /2)? δ} in the composition range 0.07 ≤ x ≤ 0.30, were prepared by standard solid-state reactions. Sample characterization and the principal phase transitions (α ? β, β ? γ and γ′ ? γ) were investigated by FT-IR spectroscopy, X-ray powder diffraction, differential thermal analysis (DTA) and AC impedance spectroscopy. For composition x = 0.07, the α ? β and β ? γ phase transitions were observed at temperatures of 451 and 536°C, respectively. DTA thermograms and Arrhenius plots of conductivities revealed the γ′ ? γ phase transition at 411 and 423°C for x = 0.20 and 0.30, respectively. AC impedance plots showed that conductivity is mainly due to the grain contribution, which is evident in the enhanced short-range diffusion of oxide ion vacancy in the grains with increasing temperature. The highest ionic conductivity (5.03 × 10^?5 S cm^?1 at 300°C) was observed for the x = 0.17 solid solution with less pronounced thermal hysteresis.     

A generic equation of state for liquid crystalline phases of hard-oblate particles

A generic equation of state (EoS) is developed for the hard cylindrical disc model to describe the isotropic phase of hard cut-sphere particles introducing a correction parameter to incorporate the negative contributions from higher-order virial coefficients. The isotropic–nematic–columnar phase diagram of hard cut-sphere fluids is investigated combining the new EoS with a scaled Onsager free energy for the nematic phase and an extended cell theory for columnar phase. By mapping the virial coefficients of an oblate spherocylinder on to those of the cylindrical disc (which are known algebraically), the new generic EoS is used to describe the isotropic and nematic phases of hard oblate spherocylinder particles. The predictions of the generic EoS are compared with available simulation data.     

Ionic conductivity of PVdF-co-HFP/LiClO4 in terms of free volume defects probed by positron annihilation lifetime spectroscopy

ABSTRACT

Polymers based on ionic conducting materials have important interest because of their potential applications in polymer electrolytes and membranes for fuel cell application. PVdF-co-HFP poly(viniliden-co-hexafluoropropylene) was chosen as a polymer matrix because of its high ionic conductivity and better mechanical properties. Polymer matrix composites were prepared with various amounts of LiClO₄ salt by a solution casting method. The sample-ionic conductivity measurements were recorded by AC impedance analyzer at different frequencies from 0.1?Hz to 20?MHz and at different temperatures from 273 to 373?K.

The changes of nanoscopic free volume and free volume fraction in these materials were investigated in terms of temperature from 273 to 373?K using Positron Annihilation Lifetime Spectroscopy (PALS) and Simha-Somcynsky (SS) Hole Theory. The free volume had a bump at about 3% in weight percentage of the salt and there is a slight increase after 10%. The effects of weight percentages of LiClO₄ and temperature were investigated. The mechanism of the ac ionic conductivity was presented in terms of the free volume models, however thermo-occupancy function justifies the best accurate representation of the data.     

Phase transitions and ionic conductivity of BaBi x O1.5x+1 (x≥5) oxides

Crystals of the BaBi _x O_1.5x+1 family are studied using X-ray diffraction, calorimetric, and impedance methods. It is shown that the compounds with x>5 are thermally stable in the temperature range as wide as 300–870 K, in spite of the first-order phase transition with a large heat effect. The conductivity is found to be anisotropic both in low- and high-temperature phases.     

Dielectric studies of the phase transition in {N(CH3)4}2HgCl4

Dielectric properties of single-crystal {N(CH₃)₄}₂HgCl₄ (structure at room temperature; orthorhombic Pmcn) have been measured in a temperature range from 4 K to about 370 K. The dielectric constant along the a-, b-, and c-axes shows a break at 278 K. No other anomalies are detected in the temperature range studied. The transition temperature increases linearly with increasing hydrostatic pressure at a rate of 0.20 K/MPa. Twin boundaries are observed in the low-temperature phase on b-plate specimens. The results indicate that the phase transition in {N(CH₃)₄}₂HgCl₄ is ferroelastic, as in {N(CH₃)₄}₂XBr₄ (X: Mn, Co, Zn).     

Phase transitions in CuBiP2Se6 crystals

Investigation results of dielectric (20?Hz–1?MHz) properties of layered CuBiP₂Se₆ crystals are presented. The temperature dependence of the static dielectric permittivity reveals the first-order “displacive” antiferroelectric phase transition at T _c?=?136?K. In the paraelectric phase, at low frequencies, dielectric spectra are highly influenced by the high ionic conductivity with the activation energy of 2473?K (0.21?eV). In the antiferroelectric phase the electrical conductivity and its activation energy (531.1?K (0.045?eV)) are considerably smaller. At low temperatures, the temperature behaviour of the distribution of relaxation times reveals complex freezing phenomena. A part of long relaxation time distribution is strongly affected by external direct current (DC) electric field and it is obviously caused by antiferroelectric domain dynamics.     

High pressure phase diagram and phase transition kinetics of PbSe

Abstract

The cubic to orthorhombic transition in PbSe is investigated by electrical resistivity measurements up to 7 GPa and for temperatures between 20 °C and 300 °C. The phase diagram is constructed and the kinetics of the transition is discussed.     

Phase transition of samarium under high pressure

Abstract

The DAC X-ray power photograph method was employed for studing the phase transition of samarium up to 26.3 GPa. The experimental results show that the dhcp and fcc high pressure phase of Sm appeared at about 4.0 and 12.5 GPa and room temperature respectively. The dhcp phase was kept until 19.6 GPa. A model for Sm-type -? dhcp -? fcc phase transition is provided in this paper.     

AC conductivity analysis and dielectric relaxation behavior of (C6H20N3)BiBr6.H2O

The N‐(3‐ammoniumpropyl)‐1,3 diammoniumpropane hexabromobismuthate (III) monohydrate exhibits a structural phase transition at T = 330 °K, which has been characterized by differential scanning calorimetric. The alternating current electrical conductivity and the dielectric relaxation properties of the (C₆H₂₀N₃)BiBr₆.H₂O compound have been investigated by means of impedance spectroscopy measurements over a wide range of frequencies and temperatures, 100 Hz–1 MHz and 290–355 °K, respectively. The Z′ and Z″ versus frequency plots are well fitted to an equivalent circuit consisting of series of combination of grains and grain boundary elements. The frequency dependent alternating current conductivity is well described by Jonscher's universal power law: σ(ω,T) = σ_DC(T) + A(T)ω^s(T). The nature of direct current conductivity variation suggests the Arrhenius type of electrical conductivity. Furthermore, the modulus plots can be characterized by full width at half height or in terms of a non‐experiential decay function φ(t) = exp(?t/τ)^β. The variation of the value of these elements with temperatures confirmed the result detected by differential scanning calorimetry measurements. Thus, the near values of activation energies obtained from the impedance and modulus spectra confirm that the transport is through an ion hopping mechanism. Copyright © 2015 John Wiley & Sons, Ltd.