Dielectric Relaxation and Beyond Limiting Behavior of Alternating‐Current Conductivity in a Supermolecular Ferroelectric

A cyclen‐based hybrid supermolecule crystal, [(FeCl₂)(cyclen)]Cl ( 1 ), where cyclen=1,4,7,10‐tetraazacyclododecane, was prepared using a liquid–liquid diffusion approach. The variable crystal structures exhibit that compound 1 belongs to an orthorhombic crystal system, Pna2₁ space group (point group C_2V) in the temperature range of 150–400 K. This hybrid supermolecule shows a dielectric relaxation behavior around room temperature, and the ferroelectric nature of 1 has been directly verified by hysteresis measurements. In addition, the AC (alternating current) conductivity study reveals that the 1 displays a beyond limiting behavior. These interesting findings are for the first time reported in the field of supermolecular ferroelectrics. This study may open a new way to construct supermolecular ferroelectrics and give insights into their conductor behavior.     

Ferroelectric and piezoelectric properties of a quenched poly(vinylidene fluoride-trifluoroethylene) copolymer

The ferroelectric and piezoelectric properties of melt-quenched unoriented poly(vinylidene fluoride-trifluoroethylene) (73 : 27) copolymer films as a function of the number of poling cycles have been studied. The investigation revealed that quenched films exhibit a decrease in D-E hysteresis behavior as the number of poling cycles increases when the samples are poled at room temperature. Corresponding decreases in remanent polarization, Pr, as well as small increases in the coercive field, Ec, were observed as the material was subjected to successive poling cycles. The piezoelectric coefficients, d₃₁ and e₃₁, also decreased as the number of poling cycles increased. In addition, a clear reduction in the “apparent” Curie transition temperature between unpoled and poled material was observed. Preliminary evidence indicates that films quenched from the melt to below T_c do not form a stable ferroelectric crystal phase as previously believed. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 2671–2679, 1997     

Ferroelectric properties of nylon 11 and poly(vinylidene fluoride) blends

Both poly(vinylidene fluoride) (PVF₂) and nylon 11 are ferroelectric polymers, and have been extensively studied over the past two decades. Blend films were made from mixed powders of these two polymers, which were then melt pressed and cold drawn. The ferroelectric properties of these blend films were investigated. The remnant polarization, P_r, was found to vary with composition, and to be 60% larger than that of either component at a 50/50 (by weight) composition where P_r exhibited a maximum of about 90 mC/m². The magnitude of the coercive field, E_c, also exhibited a maximum at this composition. Both P_r and E_c are also observed to change significantly with the draw ratio. The results are discussed based on a two-phase dielectric composite model. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 3217–3225, 1999     

Equivalent circuit of Warburg impedance

Justification is presented for the principles of construction of the simplest equivalent circuit for Warburg impedance that follow from the properties of the conductivity function (CF) and logarithmic conductivity function (LCF) of RC two-terminal networks with lumped and distributed parameters. The possibility is shown of presenting CF in the form of a sum of parameters of the same type or in the form of a product of factors of two types. The methods of construction of asymptotic LCFs are considered. Relationships are obtained that allow modeling Warburg impedance with two and three serial capacitive circuits on the basis of the performed analysis.     

Synthesis,characterization, optical,thermal and electrical properties of polybenzimidazoles

The variation of dielectric constant and dielectric loss of two novel polybenzimidazole (PBI) were studied at constant temperature with variable frequency. The polymers have shown maximum dielectric constant at low applied frequency 50 Hz at 393 K due to the space charge polarization. The AC conductivity and activation energy of polymers were arrived from dielectric constant and dielectric loss values. PBIs were synthesized by the oxidative polycondensation of benzimidazole monomers, 2-(1H-benzo [d] imidazole-2-yl)-4-bromophenol (BIBP), and 2-(1H-benzo [d] imidazole-2-yl)-6-methoxyphenol (BIMP) in an aqueous alkaline medium using NaOCl as oxidant. The monomers and polymers were characterized by various spectroscopic techniques. Fluorescence spectra of monomers and polymers showed their λ _max emission in the region of 472–479 and 463–472 nm respectively. The electrical conductivities of iodine doped polybenzimidazoles were measured by four-point probe technique and it increases with increase in iodine vapour contact time. The electrical conductivity values were correlated with the charge density on imidazole nitrogen obtained from Huckel calculation method. Both the PBI are having reasonably good thermal stability and are shown by high carbines residues of around 40% at 500°C in thermogravimetric analysis.     

Sorption and conducting properties of perfluorinated MF-4SC membranes in aqueous solutions containing phenylammonium ions

A comparative study of the sorption effect is performed for nitrogen-containing ammonium, phenylammonium (PhA⁺), and tetrabutylammonium (TBA⁺) cations on conducting and hydrophilic properties of protonic form of perfluorinated sulfocationite MF-4SC membrane. Conductometric method was used to study thermodynamic equilibria in the systems of perfluorinated MF-4SC membrane—aniline in the acid solutions of variable composition (PhA⁺/HCl and PhA⁺/H₂SO₄). Concentration constants of ion-exchange equilibrium are calculated for a MF-4SC membrane on the basis of these data. These constants in the solutions of aniline with HCl and H₂SO₄ are 10.3 and 27.0, accordingly. The choice of sulfuric acid as background electrolyte for matrix polyaniline synthesis is substantiated.     

Dielectric and Ferroelectric Properties of Sol-Gel Derived YMnO3 Films

There has been considerable interest in ferroelectric (FE) films especially for non-volatile memories and ultra high density DRAM applications. Such FE films typically consist of lead zirconate titanate (PZT) with novel oxide contacts, or layered perovskite such as Sr2Bi2TaO9. Recently, there have been reports of sputtered YMnO3 films which exhibit a single polarization axis and do not contain any volatile species of Pb or Bi. Single crystal YMnO3 exhibits satisfactory polarization (6 C/cm2) and low coercive field (<20 kV/cm). Additionally, the dielectric constant of YMnO3 is quite low (<30) which should facilitate ferroelectric switching. In this study, sol-gel derived YMnO3 films were prepared on platinized Si wafers and their dielectric and ferroelectric properties were characterized. Their electrical properties will be discussed with respect to Y/Mn stoichiometry ratio, hexagonal phase development and processing conditions. The potential of YMnO3 as a material in non-volatile memories is evaluated.     

Structural and electrical properties of crystals of substituted polyaniline

The simultaneous polymerization and crystallization of aniline has been reported earlier. In this article, the X‐ray crystal structure analysis, SEM morphological analysis and electrical properties of such crystals of oligo‐polyanilines are being reported. The structural analysis shows a pseudo‐orthorhombic lattice. The SEM images reveal flaky and triangular growth habit with granular overgrowths on the surface. The bulk conductivities achieved vary from 10^?5 S/cm to 10^?7 S/cm as the oxidant concentration is reduced from 5 to 0.1%. The temperature dependence showed a transition point upto which there is a decrease in current and above which the current increases. The ESR studies reveal polarons involved in charge conduction and their concentration is proportional to the oxidant concentration. The X‐ray patterns, conductivities, and ESR results have been correlated with the degree of polymerization results obtained from GPC studies. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1127–1137, 2007     

Measurement of viscosity and electrical conductivity and a thermodynamic model

According to the need of industrial design and application of new desulfurization technique, we determine viscosities and electrical conductivities of dilute SO₂ mixture gas in dimethyl sulfoxide mixture absorbents, and establish a thermodynamic model based on experimental data. The viscosities and electrical conductivities calculated by the model show good agreement with experimental data.     

Crystal structure,Hirshfeld surface analysis,Thermal study and Conduction mechanism of [(C4H9)4P]3Bi2Cl9 compound

A novel tris (tetrabutylphosphonium) nonachlorodibismuthate (III) compound has been synthesized and characterized by a single‐crystal X‐ray diffraction, calorimetric, IR spectroscopy and electrical measurements. X‐ray diffraction analysis at room temperature reveals that the title compound belongs to the monoclinic system with P2₁/c space group. The unit cell dimensions are: a = 19.201(6) Å, b = 16.743 (5) Å, c = 22.396 (8) Å, β = 98.96 (2)° and Z = 4. The crystal structure was solved down to R equal to 0.035 for 5597 independent reflections. The crystal package is provided by electrostatic interactions and hydrogen bonds (C‐H ^…. Cl). Intermolecular interactions present in the grown single crystal were analyzed by Hirshfeld surface and 2‐dimensional fingerprint plot. The differential scanning calorimetry reveals one order–disorder phase transition at 400 ± 5 K.The electrical conductivity were carried out in the frequency range 200 Hz–1 MHz at various temperatures 343–413 K using impedance spectroscopy technique. The obtained results were analyzed by fitting the experimental data to an equivalent circuit model. The temperature dependence of alternating and direct current conductivities confirms the observed phase transition in the calorimetric study; they were described in terms of Arrhenius relation. AC conductivity measurements reveal that the conduction depends on both frequency and temperature, this agrees well with Correlated Barrier Hopping model in phase I and II.     

微流控非接触电导检测芯片的设计与模拟

采用微加工技术制作了微芯片非接触电导检测系统。考察了激励电压、激励频率、样品溶液浓度对输出信号的影响,采用wewb 5.0软件对检测池的模拟电路进行了仿真模拟。通过比较试验和模拟结果,发现两者具有较好的一致性,说明模拟电路较好地反映了非接触电导检测池的电气特性。     

An enhancement on electrical properties of carboxymethyl cellulose-NH4Br based biopolymer electrolytes through impedance characterization

In this work, the formulation of biopolymer electrolytes (BEs) system has been accomplished by incorporating various plasticizers with carboxymethyl cellulose–NH₄Br through solution casting technique. The ionic conductivity at room temperature of BEs system was achieved at ～10^?4 S cm^?1 with addition of 25?wt% NH₄Br and enhanced to ～10^?3 S cm^?1 when plasticizers were added. The temperature-dependence of the BEs system exhibits Arrhenius behavior. Jonschers power law was used to study the electrical properties and shows that the highest conducting BEs system can be represented by overlapping overlapping a large polaron tunneling model for poly(ethylene glycol) system a, small polaron hopping model for glycerol system, and a quantum mechanical tunneling model for ethylene carbonate system.     

Preparation and Characterization of a Sol-Gel Prepared Ferroelectric Sandwich Structure

A novel silicon-based PbTiO₃/Pb(Zr,Ti)O₃/PbTiO₃ (PT/PZT/PT) sandwich structure has been prepared using a sol-gel method. The annealing temperature is greatly reduced compared with those structures without PT layers. Capacitance-voltage (C-V), leakage current-voltage (I-V), polarization-field (P-E), dielectric-frequency response and polarization fatigue of the sandwich structure are examined. The relative dielectric constant, the coercive field and the remanent polarization of the PZT films are measured to be about 900, 18 kV/cm and 16 C/cm² respectively. The current density is less than 5 × 10^–9 A/cm² below 200 kV/cm. The dielectric constant of the structure remains constant at low frequency, and decreases to some degree at high frequency. The retained polarization does not change significantly after 8 × 10⁹ read/write cycles. The PZT films are proved to have very good dielectric and ferroelectric properties. The new PT/PZT/PT sandwich structure can be valuable for memory devices and other applications.     

Structure and properties of semicrystalline polymers via high-frequency acoustic and x-ray measurements. I. Ferroelectric P(VDF/TrFE) copolymer

Acoustic, opto-acoustic, and x-ray investigations have been performed in order to study the influence of irradiation, electrical poling, and mechanical orientation on the morphology of ferroelectric random copolymers of vinylidene fluoride and trifluorethylene {P[VDF/TrFE] (70/30)}. The influences of these different treatments on the molecular orientation distribution of the amorphous and crystalline phases are discussed, as well as their influences on the crystallinity of the material. The elastic stiffness and the related viscosity tensors of P[VDF/TrFE] (70/30), the elastic stiffness modulus of the amorphous matrix, and the hierarchy of stiffness constants of the crystalline state have been determined. © 1993 John Wiley & Sons, Inc.     

Effect of conductive particles on the mechanical,electrical, and thermal properties of maleated polyethylene

Inclusion of conductive particles is a convenient way for the enhancement of electrical and thermal conductivities of polymers. However, improvement of the mechanical properties of such composites has remained a challenge. In this work, maleated polyethylene is proposed as a novel matrix for the production of conductive metal–thermoplastic composites with enhanced mechanical properties. The effects of two conductive particles (iron and aluminum) on the morphological, mechanical, electrical, and thermal properties of maleated polyethylene were investigated. Morphological observations revealed that the matrix had excellent adhesion with both metal particles. Increase in particle concentration was shown to improve the tensile strength and modulus of the matrix significantly with iron being slightly more effective. Through‐plane electrical conductivity of maleated polyethylene was also substantially improved after adding iron particles, while percolation was observed at particle contents of around 20–30% vol. In the case of aluminum, no percolation was observed for particle contents of up to 50% vol., which was linked to the orientation of the particles in the in‐plane direction due to the squeezing flow. Inclusion of particles led to substantial increase (over 700%) in the thermal conductivities of both composites. The addition of high concentrations of metal particles to matrix led to the creation of two groups of materials: (i) composites with high electrical and thermal conductivities and (ii) composites with low electrical and high thermal conductivities. Such characteristics of the composites are expected to provide a unique opportunity for applications where a thermally conductive/electrically insulating material is desired. Copyright © 2015 John Wiley & Sons, Ltd.     

Water sorption and electrical/dielectric properties of organic-inorganic polymer blends

Organic-inorganic polymer blends (OIPB) were obtained by reaction of organic and inorganic oligomers. The organic oligomer was synthesized with 2,4-toluene diisocyanate (TDI) and oligooxypropylene glycols (OPG) with various molecular weights (MW). The inorganic component was a water solution of sodium silicate. The OIPB obtained are hydrophilic and have great water sorption ability (the relative weight of sorbed water reaches 2000 %). The kinetics of water sorption and the changes of electrical conductivity during sorption were studied. Sorption ability, and mechanical, electrical and dielectric properties of OIPB depend on molecular weight of OPG: conductivity increases with increasing MW, whereas the sorption ability correlates with the mechanical properties. The influence of the inorganic phase content on the electrical and dielectric properties was studied as well.     

Processing and Characterization of Sol-Gel Derived Modified PbTiO3 for Ferroelectric Composite Applications

Powders of (Pb_0.8Ca_0.2)(Ti_0.99Mn_0.01)O₃ have been prepared by sol-gel processing. A tetragonal phase is formed after heat treatment at as low as 800°C. The tetragonality was found to be 1.053±0.005 and Curie temperature 315°C. Composite films with 0–3 connectivity were prepared from 800°C heat treated powders and P(VDF-TrFE) by the solvent casting technique. Composites poled at 20 MV/m, exhibited a pyroelectric coefficient of 17.4 μC/m²K and a pyroelectric figure of merit (FOM_p=p/ε) of 0.51 μC/m²K.     

Thermal, mechanical and electrical properties of copper powder filled low-density and linear low-density polyethylene composites

Low-density polyethylene (LDPE) and linear low-density polyethylene (LLDPE) with different copper contents were prepared by melt mixing. The copper powder particle distributions were found to be relatively uniform at both low and high copper contents. There was cluster formation of copper particles at higher Cu contents, as well as the formation of percolation paths of copper in the PE matrices. The DSC results show that Cu content has little influence on the melting temperatures of LDPE and LLDPE in these composites. From melting enthalpy results it seems as if copper particles act as nucleating agents, giving rise to increased crystallinities of the polyethylene. The thermal stability of the LDPE filled with Cu powder is better than that for the unfilled polymer. The LLDPE composites show better stability only at lower Cu contents. Generally, the composites show poorer mechanical properties (except Young's modulus) compared to the unfilled polymers. The thermal and electrical conductivities of the composites were higher than that of the pure polyethylene matrix for both the LDPE and LLDPE. From these results the percolation concentration was determined as 18.7 vol.% copper for both polymers.     

Composite materials based on zeolite 4A for adsorption heat pumps

Some additives and binders were chosen for the preparation of 4A-zeolite-based composites with high equivalent thermal conductivity for heat pumps application. Additives (SiC, Si₃N₄, graphite) and binders (PTFE, Al(OH)₃) were tested for their effectiveness in terms of equivalent thermal conductivity and maximum water adsorption capacity of the composites. The influence of the equivalent thermal conductivity of the composite adsorbents on the specific power of the heat pump was also calculated. Results show a significant improvement in the equivalent thermal conductivity of the composite samples which are prepared using aluminum hydroxide as binder, over that of zeolite pellet beds. Such composite materials could be used to build adsorption heat pumps with higher specific power and, consequently, with lower investment cost.