Hydrothermal Synthesis and Dielectric Characterization of a Double Perovskite Ba2FeSbO6

A double perovskite oxide Ba₂FeSbO₆ was hydrothermally synthesized and structurally characterized by X-ray diffraction. This solid compound shows a single phase and has a trigonal structure with space group R m and cell parameters of a=0.57261 nm and c=1.40244 nm. The dielectric constant and loss tangent of the solid measured in a frequency range from 100 Hz to 1 MHz at temperatures from 313 K to 513 K reveal a relaxation process of frequency dependence of the real part(ε') of dielectric constant and dielectric loss tand. The frequency dependence of electrical property led to the framework of conductivity and electric modulus formalisms. The scaling behavior of imaginary part of electric modulus suggests that the relaxation describes the single mechanism at various temperatures. The variation tendency of the alternating current impedance indicates the thermally activated conduction process follows Jonsche’s power law.     

烷基聚葡糖苷C9.6G1.3/n-C4H9OH/n-C6H14/H2O微乳液体系的介电弛豫谱研究

The pseudotertiary phase diagram of the microemulsion system alkyl polyglucoside/n-butanol/n-hexane/water was plotted at （30.0±0.1） ℃. The dielectric measurements, including permittivity, conductivity, relaxation strength, characteristic relaxation time, etc,, were applied to investigate the microstructure of the system. Unique dielectric relaxations were observed over the frequency range of 5-10^7 Hz, taking place possibly through an interracial polarization mechanism. According to the results obtained from dielectric spectroscopy, the structures of the microemulsion O/W, BC and W/O were determined, and some dielectric and phase parameters were calculated.     

Dynamics of 4,4'-di-n-heptylazoxybenzene (HAB) studied using dielectric and 2H NMR relaxation measurements

Results of studies of 4,4'-di-n-heptylazoxybenzene (HAB) in the isotropic, nematic and smectic A phases are presented. Two experimental methods were employed: broad band dielectric spectroscopy and nuclear magnetic resonance spectroscopy. The complex dielectric permittivity, ε*(ω)=ε'(ω)-iε'(ω), was measured in the frequency range 1 kHz-4 GHz. This allowed two main relaxation processes to be separated in all the phases studied: the low frequency (l. f.) process connected with molecular reorientations around the short axes, and the high frequency (h. f.) process connected with the rotations around the long axes. The corresponding relaxation times and activation enthalpies were obtained. The l. f. relaxation time changes step-wise at the phase transitions, whereas the h. f. relaxation time passes smoothly through all the phases. The measurement of ²H spin-lattice relaxation times was carried out throughout the mesophase range at 61.38 MHz. These data were analysed together with the relaxation times measured at 10.00 and 46.04 MHz, available from previous studies. Using suitable theoretical models the principal components of the diffusional tensor, D_‖ and D_⊥, as well as the diffusion coefficients D_R relative to the internal rotation of the phenyl rings, were determined. The results of both studies are compared and discussed.     

Dielectric Spectroscopy Study on Vesicles of CTAB/SDBS System

IntroductionWhen the cationic and anionic surfactants in which the total carbon number is equal to or greater than 20 are mixed, then the vesicles can form spontaneously due to the strong interactions or by sonication1. Vesicle is of bilayer structure containing a closed aqueous room, resembling the structure of a real cell. So it seems to be imperative to study the membrane mimicry system like vesicle in order to understand the structure and functions of real cells further. In addition, it ca…     

Studies on the Phase Properties of Winsor Ⅰ-Ⅲ Type Microemulsions with Dielectric Relaxation Spectroscopy

The dielectric relaxation spectroscopy (DRS) of Winsor Ⅰ～Ⅲ microemulsions for nonionic surfactant octyl polyglucoside C8G1.46/1-butanol/cyclohexane/water system was studied.The experiment shows that the permittivity decreases with the increase in the frequency and clear dielectric relaxation phenomena were observed. Permittivity obviously decreases with the change of the microstructure of the microemulsion, W/O, B.C. and O/W can be distinguished by the permittivity.     

Dynamics in water-AOT-n-decane microemulsions with poly(ethylene glycol) probed by dielectric spectroscopy

Water in oil microemulsions, consisting of water, AOT and n-decane, have been used as a model system to investigate the influence of the water soluble polymer PEO on the dynamical behavior of the system. Therefore dielectric relaxation spectroscopy and conductivity, extracted from dielectric spectroscopy, measurements in a wide frequency and temperature range have been applied. The pure microemulsion displays the known phenomenon of percolation that manifests in a steep increase of conductivity at the percolation temperature $T_\text{P}Water in oil microemulsions, consisting of water, AOT and n-decane, have been used as a model system to investigate the influence of the water soluble polymer PEO on the dynamical behavior of the system. Therefore dielectric relaxation spectroscopy and conductivity, extracted from dielectric spectroscopy, measurements in a wide frequency and temperature range have been applied. The pure microemulsion displays the known phenomenon of percolation that manifests in a steep increase of conductivity at the percolation temperature T_\textPT_\text{P}. The percolation temperature has been found to be strongly dependent on droplet volume fraction and droplet size. The latter additionally shows that percolation temperature and surfactant film rigidity are proportional. Far from percolation water-AOT-n-decane microemulsions display two dielectric relaxations. The slower one has a relaxation time of t ? 3·10^-6 \texts\tau \approx 3\cdot 10^{-6}~\text{s} and can be related to an interfacial polarization at the interface of the water core and the AOT shell (core relaxation). The faster one has a relaxation time of t ? 10^-9 \texts\tau \approx 10^{-9}~\text{s} and can be related to the ions in the AOT shell(shell or cluster relaxation). While the first is mainly untouched by the percolation phenomenon, the latter undergoes a slowdown and an increase of relaxation strength, both over about two decades, on approaching the percolation transition. Addition of PEO tremendously shifts the percolation transition to higher temperatures, due to adsorption at the AOT layer which leads to an increase in rigidity. Furthermore a lower phase boundary temperature evolves, below which the microemulsion phase separates. The conductivity of the microemulsion is also slightly increased with polymer. The effect on the dielectric properties is only small, where dielectric relaxation times are reduced by the polymer, while only the relaxation strength of the faster relaxation is influenced and also decreases with polymer. The decreased relaxation time of core relaxation can be either due to changes in the core to shell volume ratio or an increased conductivity of the water core. The decrease in relaxation time and strength of the shell relaxation suggest that the ion mobility in the shell increase, while the dipole moment is reduced. Additionally we applied a cluster relaxation model proposed by Cametti et al. (Phys Rev Lett 75(3):569, 1995) and Bordi et al. (J Phys, Condens Matter 8:A19, 1996) to estimate the cluster size evolution.     

苯-水-乙醇三元溶液体系的临界行为

通过等体积滴定法测定了苯-水-乙醇三元部分互溶溶液体系的会溶点曲线；测定了29.00±0.05 ℃时,等溶点附近的等温共存曲线；拟合得到苯-水-乙醇体系序参量临界指数β= 0.38 ± 0.04,序参量临界指前因子K= 1.3 ± 0.2. 说明三元部分互溶溶液体系在等温会溶点附近有非经典临界溶液理论行为, 符合Fisher重正化模型.     

Formation of fractal porous silica by hydrolysis of TEOS in a bicontinuous microemulsion

Mesoporous silica particles have been prepared by hydrolysis of TEOS (Si(OC₂H₅)₄) in bicontinuous microemulsions containing polyoxyethylene (POE) dodecylether, isooctane and water. TEOS was dissolved in a continuous water phase and hydrolyzed by the dispersed water at around the phase inversion temperature (60°C). Undulating solid materials with layered mesostructures were produced from middle-phase microemulsions in the three phase region (o/w=0.2–0.7). On the other hand, the solids obtained from the lower aqueous phase in the three phase region were found to have a heterogeneous disordered structure. Measurements of the fractal dimensions were performed in the macropore region using a box-counting method for the outline of the SEM texture. We found that the macropore size distribution in the particles prepared from the middle-phase microemulsion follows the fractal rule with a dimension of 1.7. From the results of nitrogen adsorption/desorption curves on the silica, a steep increase in the adsorption amounts was observed at a relative pressure below 0.2, and adsorption/desorption hysteresis was also observed at a relative pressure between 0.3 and 0.5. These studies suggest that the silica synthesized in the bicontinuous microemulsion mesostructure has a very broad size range from micro to macropores with a fractal distribution.     

SiO2/聚乙二醇非牛顿流体流变性能研究

利用应力控制流变仪考察了SiO₂/聚乙二醇分散体系稳态和动态的流变性能. 实验结果表明, 该体系具有剪切变稀和可逆的剪切增稠现象. 稳态应力实验中, 当应力较小时, 体系具有剪切变稀现象, 而在剪切应力(σ)大于临界剪切应力(σ_c^s, σ_c^s=9.99 Pa)后, 体系粘度急剧增大. 在动态实验中, 剪切应力小于临界剪切应力(σ_c^o, σ_c^o=15.85 Pa)时, 储能模量G′减小, 耗能模量G″与复合粘度η*基本不变, 但σ＞15.85 Pa后, G′、G″及η*同步增大, 且在所研究的应力范围内, G″均大于G′. 同时还考察了测试频率、分散相含量以及分散介质平均分子量的差别对流变性的影响. σ_c^o随测试频率的增大而变大; SiO₂质量分数越大, σ_c^o基本不变, 但增稠现象变得更明显; 与平均分子量小的PEG200体系相比, 平均分子量大的PEG400体系, σ_c^o并未发生改变, 但在增稠之前体系的粘度较低, 增稠之后体系粘度增大的幅度较大.     

Microdynamics of solid anilinium chloride

Intraionic C₃ reorientation of the anilinium NH⁺₃ group was evidenced by measurements of the temperature dependence of the proton spin—lattice relaxation time, by rotating frame experiments and cw NMR data. Analysis of the results yielded a rotor hindering potential E = 33.6 kJ/mole and τ_o = 4 × 10⁻¹³ s.     

An Investigation of Structure Transition in Sodium Dodecyl Trioxyethylene Sulfate／n-Butanol／n-Octane／Water System by Dielectric Relaxation Spectroscopy Method

IntroductionDielectricrelaxationspectroscopy(DRS) possess esanimportantpositioninmodern physicochemicalanalysis .Dielectricmeasurementscanbedoneinsuchawidefrequencyrangeof 10 - 5— 10 11Hz ,makingitpossibletodetectallkindsofprocessesofvarioussys tems[1] .DRSisbasedonthepolarizationtheory ,in cludingdipolereorientation polarization ,interfacialpolarization ,ionicpolarizationandelectronicpolariza tion ,ofwhichinterfacialpolarizationis prevalent.Whenthereexistsaclearphaseinterface ,aninterfa c…     

A new mean field SA-SA' critical point in a symmetry breaking field

We consider a S_A-S_A' critical point in the presence of a symmetry-breaking external magnetic (electric) field with a positive magnetic (dielectric) anisotropy or a dislocation layer. Via a renormalization group analysis of the model hamiltonian, we show that the upper critical dimensions below which mean-field theory breaks down is d_c = 2·5. Thus the S_A-S_A' transition in three dimensions becomes mean-field like in the presence of a symmetry-breaking field. We estimate the reduced temperature region where we can expect to see the mean field S_A-S_A' critical point in the presence of a magnetic field or a dislocation layer.     

Fractal behaviour of carbon black and smectite dispersions by small angle neutron scattering

From dielectric spectroscopy on mechanically sheared dispersions of carbon black in mineral oil it was known that the distribution of relaxation times was invariant irrespective of the applied shear rate. From this observation fractal behaviour was suspected and a small angle neutron scattering experiment was set up for confirmation. Indeed, by this experiment a fractal dimension has been found of d=2.19, a value which is perfectly comparable tod=2.0 found by dielectric spectroscopy.The dielectric behaviour of the smectite dispersion is different from the carbon black and small angle neutron scattering confirms this. Ad-value of 2.8 has been found, pointing to a more compact object than could be expected from a fractal.     

X-ray diffraction, Raman study and electrical properties of the new mixed compound [Rb0.44(NH4)0.56]2HgCl4 · H2O

Differential scanning calorimetry of [Rb_0.44(NH₄)_0.56]₂HgCl₄ · H₂O material showed three anomalies at 340, 355 and 424 K, respectively. The room temperature phase has space group Pcma (a=8.433(1) Å, b=9.1817(9) Å and c=11.954(1)). Phase II (T=350 K) is disordered and exhibits orthorhombic symmetry (a=8.456(13), b=9.202(9) and c=12.011(10) Å). Hydrogen bonding, the nature and the degree of structure (dis)order and the mechanisms of the transitions are discussed. The dielectric constant ^′ at different frequencies and temperature revealed a phase transition at T=340 K related to NH₄⁺ reorientation and H⁺ diffusion, and a characteristic increase above 355 K, which might be due to loss of water of crystallization. Transport properties in this compound appear to be due to an Rb⁺/NH₄⁺ and H⁺ ions hopping mechanism.     

Percolation in alkyl polyglycoside microemulsions

Mixtures of oil, water, alkyl polyglycosides and long-chain alcohols form almost-temperature-invariant microemulsions. The phase behaviour depends on the content of cosurfactant, usually long-chain alcohols. We show that the system C_8/10G_1.5/octane/water/octanol exhibits cosurfactant-induced percolation phenomena. The percolation transition from an electrically conducting oil-in-water microemulsion to an electrically non-conducting water-in-oil microemulsion with increasing cosurfactant content is observed by measurements of electrical conductivity and time-resolved electric birefringence. The field-off relaxation time yields information on the internal length scale. The scaling behaviour of field-off relaxation times and Kerr constants with respect to the percolation point leads to insight into the influence of cosurfactant on phase behaviour. Received: 27 July 1999/Accepted: 8 February 2000     

非绝热分子动力学模拟A位阳离子对钙钛矿热载流子弛豫的影响

钙钛矿具有优异的光学和电学性质,近年来成为太阳能电池领域的研究热点.大量实验报道钙钛矿热载流子弛豫时间变化顺序为CsPbBr₃>MAPbBr₃(MA=CH₃NH₃)>FAPbBr₃[FA=HC(NH₂)₂],但A位阳离子(Cs⁺,MA⁺,FA⁺)对弛豫快慢的影响机制仍不明确.采用基于含时密度泛函理论的非绝热动力学方法研究了上述3种钙钛矿热电子和热空穴的能量弛豫动力学,计算得到的热载流子弛豫时间与实验结果吻合.结果表明,A位阳离子通过静电和氢键作用影响其与无机Pb—Br骨架的电子-振动耦合,使非绝热耦合强度遵从FAPbBr₃>MAPbBr₃>CsPbBr₃的变化趋势,进而使热载流子弛豫时间尺度变化趋势与之相同,表明合理选择A位阳离子可以优化钙钛矿太阳能电池的性能.     

Upper and lower critical solution temperatures in polybutadiene-alkane systems : Effect of the surface-to-volume ratio of the polymer

Cloud point curves (CPC) have been measured for 1–4 cis polybutadiene (M_r = 40,000–830,000) in n-hexane, 2-methyl-hexane, 2,2,3 trimethylbutane and 2,2,4 trimethylpentane. These four systems show upper and lower critical solubility temperatures which approach one another as the molecular weight increases. An hourglass-shaped CPC is found for two systems. The CPC are found to be much more dependent on polymer concentration than is usual. Calculated (Prigogine, Patterson, Flory theories) and experimental critical temperatures, critical volumes and shapes of the CPC are in much better agreement for these systems than for other systems involving polystyrene, polyisobutylene or polybutene-1. Analysis of these results with those for other systems in the literature indicates the importance of the surface-to-volume ratio s of the polymers. A small value of s = s₂/s₁ (0·5–0·8) for thick polymer chains improves the calculated value of the critical temperature while s = 1 is quite good for thin polymer chains such as polybutadiene and polyethylene.     

Density functional theory analysis of CaRgn complexes: (Rg=He, Ne, Ar; n=1–4)

CaRg_n⁺ (Rg=He, Ne, Ar) complexes with n=1–4, are investigated by performing using the B3LYP/6-311+G (3df) density functional theory calculations. The CaHe_n⁺ (n=1–4) complexes are found to be stable. In the case of CaNe_n⁺ and CaAr_n⁺, stable structures and stationary point were found only for n=1 and 2. For n=3 in the C_3V and the D_3h point group as well as for n=4 in the T_d (tetrahedral) point group a saddle point (imaginary frequency) is observed and global minimum could be obtained along the potential energy surface.     

阴离子表面活性剂SDBS胶束溶液的介电弛豫行为

用射频介电谱方法研究了0.1-80 mmol·L-1浓度的十二烷基苯磺酸钠(SDBS)水溶液体系的介质弛豫行为. 测量发现频率接近107 Hz时, 在临界胶束浓度(CMC)附近出现显著的介电弛豫现象. 采用Cole-Cole函数拟合SDBS体系介电数据, 其拟合参数具有明显变化规律: 介电增量(△ε)随SDBS摩尔浓度(cs)的增加而增大, 表现为两种线性关系, 并在cs=36 mmol·L-1附近出现拐点; 特征弛豫时间(τ0)却在cs=45 mmol·L-1出现极小值. 利用胶束电模型分析了介电弛豫机制, 认为束缚Na+对离子数量和胶束体积变化是引起介电增量和特征弛豫时间变化的两个重要原因.