Studies on the electronic transport and optical properties of some new chelate modified polysulfones in thin films

The studied polymers (chelate modified polysulfones) have been prepared by the polycondensation reaction between chloro‐end‐capped polysulfones and bis(2,4‐dihydroxybenzaldehyde)Cu²⁺ in the dymethyl sulfoxide/dichlormethane system, in the presence of an aqueous sodium hydroxide solution. The temperature dependence of electrical conductivity and Seebeck coefficient of the respective polymers was investigated using thin‐film samples, deposited from chloroform solutions onto glass substrates. The polymers under study have typical semiconducting properties. The values of some characteristic parameters of the investigated polymers (for example, activation energy of electrical conduction, ratio of carrier mobilities, etc.) have been determined. The nature of the electrical conduction mechanism is discussed. The values of the optical bandgap energy are determined from the absorption spectra. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 100–106, 2006     

Theoretical investigations of electronic structure and charge transport properties in polythiophene‐based organic field‐effect transistors

Regioregular poly(3‐hexylthiophene) (P3HT) is a hole transport polymer material used in organic field‐effect transistors (OFETs) and can reach mobilities as high as 0.1 cm² V^?1 s^?1. Factors that affect the charge mobility and the transport mechanisms of P3HT‐based OFET systems are therefore of great importance. We use quantum mechanical methods to interpret the charge mobility and the transport properties of self‐assembled P3HT molecules along the intra‐chain and inter‐chain directions. Our approach is illustrated by a hopping transport model, in which we examine the variation of charge mobility with torsional angle and the intermolecular distance between two adjacent thiophene segments. We also simulate packed P3HT structures via molecular dynamics (MD) simulations. The MD results indicate that the resultant mobility along the π?π inter‐chain direction is significantly less than that along the intra‐chain direction. Accordingly, the main charge‐transfer route within the P3HT ordered domains is an intra‐chain rather than an inter‐chain one. The calculation result for the inter‐chain hole mobility is around 10^?2 cm² V^?1 s^?1, which is consistent with experimental data from P3HT single fibril. Copyright © 2009 Society of Chemical Industry     

Electrical properties and transport conduction mechanism of nitrile rubber/poly(vinyl chloride) blend

The current–voltage characteristics of acrylonitrile butadiene rubber (NBR)/poly(vinyl chloride) (PVC) blends are studied as a function of sample temperature and PVC content. These samples showed ohmic behavior up to (225 V), after this value the behavior become SCLC (space charge limited conduction). The results obtained show that the charge carriers are generated by Richardson–Schottky emission from the electrode as well as from trapped ionic impurities at high fields. The activation energy of the prepared samples was calculated by using Arrhenius equation. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Synthesis of copper chloride and cobalt chloride doped polyanilines and their magnetic and alternating‐current transport properties

Polyaniline (PANI) was synthesized by the well‐known oxidative polymerization of aniline with ammonium peroxodisulfate as the oxidant. The morphological, structural, thermal, optical, magnetic, and electrical properties were characterized with scanning electron microscopy, X‐ray diffraction, Fourier transform infrared, thermogravimetric analysis, differential scanning calorimetry, ultraviolet–visible spectroscopy, room‐temperature magnetic measurements, and low‐temperature electrical transport measurements by the standard four‐probe method. Greater thermal stability and crystallinity were observed in doped PANI versus pure PANI. Magnetic measurements showed that the magnetic susceptibility was field‐dependent. Positive and negative susceptibility values were observed. This may have been due to the interactions of magnetic ions among interchains or intrachains of the polymer matrix. The alternating‐current (ac) conductivity was measured in the temperature range of 77–300 K in the frequency range of 20 Hz to 1 MHz. The frequency‐dependent real part of the complex ac conductivity was found to follow the universal dielectric response: σ′(f) ∝ f^s [where σ′(f) is the frequency‐dependent total conductivity, f is the frequency, and s is the frequency exponent] The trend in the variation of the frequency exponent with temperature corroborated the fact that correlated barrier hopping was the dominant charge‐transport mechanism for PANI–CoCl₂. An anomalous dependence on temperature of the frequency exponent was observed for PANI–CuCl₂. This anomalous behavior could not be explained in terms of existing theories. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Investigation of electrical and optical properties of polyvinyl acetate doped with some polymers

Polyglycerol (PG) and polytriethanolamine(PTEA) have been prepared. The electrical resistivity (ρ) and the optical absorption of polyvinylacetate (PVAc) doped with polyglycerol (PG), polyaniline (PA), and polytriethanolamine (PTEA) have been studied. It was found that the conduction was mainly ionic in the temperature range from 20 to 120°C. The resistivity decreased with the increase of the dopant cocentration. The optical absorption spectra were determined in the wavelength range 400–2500 nm. The analysis of the absorption spectra showed that the intensity of the bands is remarkably affected by the dopant concentration. The optical energy gap of pure PVAc and the samples containing different dopants were estimated. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 1558–1563, 2002     

Electrical charge transport and optical properties of a poly(methacrylate) with a new side chain and its Ni(II) complex

The electronic conductivity of poly[2‐(2‐hydroxybenzyliden hydrazino)thiazole‐4‐yl methyl methacrylate] bearing a thiazole ring, Schiff base, and hydroxyl group in its side chain and its Ni(II) complex were measured as functions of temperature and frequency. The electrical measurements show the semiconducting nature of the samples as their electrical conductivity increased with increased temperature. Also, the activation energies were below 2 eV, which places them in the semiconductor regime. The conduction mechanism in the samples is discussed. Although extrinsic conduction mechanism occurs in the polymer, intrinsic conduction mechanism take places in its metal complex. The optical absorption spectra were recorded at room temperature and the optical energy gaps of samples were determined by optical spectra. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 741–746, 2003     

Effect of magnetic field on electrical properties of nanocrystalline poly(vinylidene fluoride) samples

BACKGROUND: The electrical properties of nanocrystalline poly(vinylidene fluoride) (PVDF) samples of 20 µm in thickness were measured in terms of thermally stimulated current (TSC), conduction current and dielectric constant after application of a magnetic field. RESULTS: TSC shows the release of trapped charges inside the material that enhances the current with magnetic field. The reason for the polarity reversal of the current with reversal of the magnetic field polarity is due to the change in spin of electrons depending upon the direction of the magnetic field. CONCLUSION: The magnetic field causes trapping of charge carriers in different traps, as the reason for the increase of activation energy with increasing field. The flow of conduction current at constant temperature in magnetically polarized PVDF is governed by Poole–Frenkel and Schottky–Richardson mechanisms. The decrease in dielectric constant at a certain alternating current (AC) frequency and magnetic field with temperature is caused by magnetic polarization in addition to the AC field. Copyright © 2009 Society of Chemical Industry     

Effect of the layer charge of clay minerals on optical properties of organic dyes. A review

Interactions between clay minerals and cationic organic dyes cause significant changes in the optical, spectral and chemical properties of the chromophores. These changes are due to the formation of supramolecular assemblies of dye cations, called molecular aggregates. Numerous experiments indicate that dye molecular aggregation is sensitively controlled by the layer charge of a clay mineral. Interpretations are based on a detailed analysis of papers investigating reactions of dyes with clay minerals but also considering the reactions with other inorganic solid materials and templates. Older papers dealing with the subject and alternative interpretations of the phenomenon are analysed and critically reviewed. Significance for clay science, material sciences, nanotechnology and potential industrial applications are discussed.     

Charge transport properties of poly(N-vinylimidazole) containing [Os(N)6]2+/3+ moieties

The rate of charge transport of electrodes modified with osmium containing poly(N-vinylimidazole) has been examined as a function of the nature of the contacting electrolyte solution and of temperature. Heterogeneous electron transfer from the electrode into the polymer film has also been investigated. The charge transport parameters show that the nature of the electrolyte anion and its concentration have a large impact on the polymer morphology. In sulfuric acid the films appear significantly swollen, hydrated, and porous, while in perchlorate-containing solutions they are rather compact. Activation energies for the rate-determining step of charge transport show that, depending on the electrolyte, segmental chain motion or ion movement represents the rate-limiting process.     

Reactive flash sintering and electrical transport properties of high-entropy (MgCoNiCuZn)1-xLixO oxides

In this paper, high-entropy (MgCoNiCuZn)_1-xLi_xO oxides (x = 0, 0.1, 0.15, 0.2, and 0.3) were synthesized via reactive flash sintering (RFS), and the effect of RFS process on the microstructure and electrical property of the materials were studied. The Li-doped materials exhibited a mixed ionic–electronic transport behavior. The oxidation of Co²⁺ into Co³⁺ upon Li incorporation into the materials synthesized via the conventional solid-state reaction route was not evidenced in the flash sintered materials. Instead, the charge unbalance in the Li-doped materials synthesized via RFS was compensated by oxygen vacancies and holes in the valence band of the oxides, which were accounted for the ionic conduction and electronic conduction, respectively. The ionic conductivity increased upon increasing the Li concentration as more oxygen vacancies were formed. The attraction between defects with different charges (Li_M^/ and V_O^••), which formed defect complexes, led to a decrease in the mobility of the defects, thus resulting in a less pronounced increase in the ionic conductivity at high Li concentrations. The change in the charge compensation mechanism of the materials indicates that the microstructure of such kind of oxides could be altered through RFS, and thus the property may be manipulated.     

Influence of grain interior and grain boundaries on transport properties of scandium-doped calcium zirconate

Calcium zirconate-based protonic conductors are currently the most promising electrolyte for high-temperature hydrogen sensors, however, protonic conductors exhibit mixed protons, oxygen vacancies and electron-holes conduction above 700°C, and the protons transport number is significantly influenced by the atmosphere. Therefore, the relationship between protons transport number and oxygen/water vapor partial pressure should be established to improve the veracity of the hydrogen sensor. Herein, CaZr_0.9Sc_0.1O_3-α perovskite oxides are prepared and the influence of grain interior and grain boundaries on transport properties is systematically investigated by using with defect chemistry theory. And the relationship between protons transport number and oxygen/water vapor partial pressure should be obtained. The results indicate that the dominant conduction carriers of CaZr_0.9Sc_0.1O_3-α were protons in Ar and reductive atmospheres at 500°C-800°C, and the conductivity () and transport number () of holes are remarkably increased with increasing oxygen partial pressure. In addition, protons, oxygen vacancies and electron-holes transport properties of grain interior and grain boundaries in scandium-doped calcium zirconate reveal that grains can effectively block oxygen vacancies transport at 550°C-800°C, but grains cannot block the holes transport. Therefore, the oxygen vacancies trend to transport through grain boundaries.     

Impedance study of the charge transport at poly-o-phenylenediamine film electrodes

The measured low-frequency capacitance of the polymer film was proportional to the film thickness and showed a maximum at the formal potential of the polymer. We analyzed the relation between the capacitance and potential by taking into account the contribution of an interaction between electroactive sites. The Warburg coefficient and the width of a linear 45 ° region in an impedance diagram showed each their minima near the formal potential. These impedance data were interpreted in terms of the diffusion-migration transport of both electron and anion through the film. The results of the impedance analysis suggested that electron transport was ensured by interchain electron hopping. From the combinations of the measured kinetic parameters, we inferred that one of the two charge carriers moved much faster than the other. The obtained diffusion coefficient showed a maximum in the vicinity of a voltammetric current peak; this corresponded with the potential dependence of a coupled diffusion coefficient expected in the extreme case of electron-transport control.     

The role of Co valence in charge transport in the entropy-stabilized oxide (Mg0.2Co0.2Ni0.2Cu0.2Zn0.2)O

Many of the studies on the entropy-stabilized oxide (Mg_0.2Co_0.2Ni_0.2Cu_0.2Zn_0.2)O have been heavily application-based. Previous works have studied effects of cation stoichiometry on the entropy-driven reaction to form a single phase, but a fundamental exploration of the effects of anion stoichiometry and/or redox chemistry on electrical properties is lacking. Using near-edge X-ray absorption fine structure (NEXAFS) and electrical measurements, we show that oxidizing thin film samples of (Mg_0.2Co_0.2Ni_0.2Cu_0.2Zn_0.2)O affects primarily the valence of Co, leaving the other cations in this high-entropy system unchanged. This oxidation increases electrical conduction in these thin films, which occurs via small polaron hopping mediated by the Co valence shift from 2+ to a mixed 2+/3+ state. In parallel, we show that bulk samples sintered in an oxygen-rich atmosphere have a lower activation energy for electrical conduction than those equilibrated in a nitrogen (reducing) atmosphere. Combining feasible defect compensation scenarios with electrical impedance measurements and NEXAFS data, we propose a self-consistent interpretation of Co redox-mediated small polaron conduction as the dominant method of charge transfer in this system.     

Effects of yttrium additions on the microstructure and charge transport properties of indium tin oxide semiconductors

The effects of yttrium (Y) additions (x=0, 0.05, 0.1, and 0.2) on the microstructure, chemical structure, and electrical properties of Y_xInSnO_y (YITO) thin films, prepared using a sol-gel process were examined. The transmission electron microscopy (TEM) observations showed that the undoped InSnO (ITO) film consisted of an amorphous structure with local crystalline domains on the film surface, whereas the Y additions (x=0.05, 0.1, and 0.2) to ITO suppressed the formation of the crystalline phase. X-ray photoelectron spectroscopy (XPS) analysis showed that the Y content decreased the concentration of oxygen vacancies owing to the strong incorporation of Y with oxygen. As a result of the Y incorporation, the carrier concentration of ITO films decreased. The saturation mobility (μ_sat), the on-off ratios (I_on/off), and the sub-threshold swing (S.S) of YITO films were 1.1 cm² V⁻¹ s⁻¹, ~10⁶, and ~0.5 V decade⁻¹, respectively, which are comparable with 1.7 cm² V⁻¹ s⁻¹, ~10⁵, and ~1.17 V decade⁻¹ of ITO film. Additionally, the initial threshold voltage (V_TH) was positive shift with increased of Y addition and V_TH shift (ΔV_TH) under the positive bias stress (PBS) results decreased by Y addition.     

Investigations on the electrical and structural properties of PVA doped with (NH4)2SO4

Solid polymer electrolytes based on poly(vinyl alcohol) (PVA) complexed with ammonium sulfate (NH₄)₂SO₄ at different weight percent ratios were prepared using solution cast technique. The structural properties of these electrolyte films were examined by X‐ray diffraction (XRD) studies. The XRD data revealed that the amorphous domains of PVA polymer matrix increased with the increase of ammonium sulfate added up to 5 wt %, after which the degree of crystallinity increases. The complexation of the salt with the polymer was confirmed by Fourier transform infrared (FTIR) spectroscopy. Electrical conductivity was measured in the temperature range of 303–373 K. The conductivity was found to obey Arrhenius formula. The dielectric permittivity ε′ was studied as function of temperature and frequency, respectively.The data showed increasing in ε′ values with the increase in temperature while decreased with increase in frequency for polymer electrolyte system up to 10% of ammonium sulfate added. For values of addition greater than 10%, ε′ is independent of both temperature and frequency. The ac conductivity is found to obey the power relation. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Polymer electronic materials: a review of charge transport

This article presents an overview of the charge transport phenomenon in semiconducting polymer materials. In these disordered systems both intrinsic and extrinsic parameters play significant roles. In general, π‐electron delocalization, interchain interaction, band gap, carrier density, extent of disorder, morphology and processing of materials determine the electrical and optical properties. The chemical structure, especially the role of side groups, is quite important in both physical and processing properties. The nature of charge carriers and their role in charge transport depend on the structure and morphology of the system. Hence in several semiconducting polymer devices, the correlations among structure, morphology and transport are rather strong. The dependence of carrier mobility on temperature and electric field needs to be understood in the framework of competing models based on carrier hopping, trapping/detrapping and tunneling. Exactly what determines the dispersive/nondispersive, polaronic and correlative transport regimes is yet to be quantified. An understanding of the carrier mobility in semiconducting polymers is necessary to optimize the performance of polymeric electronic devices. Copyright © 2006 Society of Chemical Industry     

Pyroelectricity and charge transport in a copolymer of vinylidene fluoride and tetrafluoroethylene

A copolymer of vinylidene fluoride and tetrafluoroethylene shows pyroelectric and piezoelectric effects after poling. Thermal pulsing measurements indicate that the polarization in this material is highly non-uniform. The piezo/pyroelectric response of this non-uniformly poled copolymer consists of two parts: a rapid response that is the result of changes in internal polarization, and a delayed response due to reversible motion of real charge through the bulk of the material. This model explains previously reported observations of the independence of pyroelectric response over a wide range of poling conditions.     

Modification of structural,thermal, and electrical properties of PVA by addition of silicon carbide nanocrystals

SiC‐PVA nanocomposite films, synthesized using solution‐casting technique were structurally characterized using X‐ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy. Morphological studies of the SiC‐PVA nanocomposite films were carried out using Transmission electron microscopy (TEM) and Scanning electron microscopy (SEM). TEM analysis confirms that the size of SiC nanocrystals present in PVA matrix are 23 ± 9 nm, which is consistent with size calculated using XRD. SiC‐PVA nanocomposite films were further characterized for their thermal and electrical properties. Thermogravimetric/differential thermal analysis (TG/DTA) indicates that the char yield of nanocomposite films containing 3 wt % SiC nanocrystal is ～30% more than PVA. This increase in char yield is an indication of the potency of flame retardation of SiC‐PVA nanocomposite films. I‐V analysis reveals that Schottky mechanism is the dominant conduction mechanism which is responsible for the increase in conductivity of PVA with the addition of SiC nanocrystals. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42464.     

Structural and transport properties of neodymium tungstates prepared via mechanochemical activation

Nd_5.5WO_11.25-δ, (Nd_5/6La_1/6)_5.5WO_11.25-δ and Nd_5.5W_0.5Mo_0.5O_11.25-δ mixed oxides have been prepared using mechanochemical activation (MA) of Nd₂O₃-WO₃, Nd₂O₃-La₂O₃-WO₃, Nd₂O₃-MoO₃-WO₃ mixtures in a high-power planetary ball mill. Genesis of these tungstates structural properties was studied by XRD, SEM, TEM with EDX analysis, ¹H NMR, IR and Raman spectroscopy. X-ray diffraction has revealed that MA results in formation of a pure fluorite structure already after milling. High-density ceramic pellets have been obtained after sintering at 1350?°C. Transport properties of Nd_5.5WO_11.25-δ mixed oxide were improved by the partial substitution of Nd with La in (Nd_5/6La_1/6)_5.5WO_11.25-δ and W with Mo in Nd_5.5W_0.5Mo_0.5O_11.25-δ samples. For all samples the electrical conductivity values measured in a humid atmosphere (up to ~ 10^?3 S/cm at 550?°C) exceed those measured in a dry atmosphere indicating the proton character of conductivity.     

Effect of CsBr–MnCl2 mixed fillers on the crystal structure and optical and electrical properties of poly(vinyl alcohol)

Poly(vinyl alcohol) (PVA) films filled with (x)CsBr(15 ? x)MnCl₂, where 0.0 ≤ x ≤ 15%, were prepared by a casting technique. The crystal structure properties of the prepared films were examined by XRD, DTA, and FTIR. A correlation between XRD, DTA, and FTIR of the filled polymer was discussed. Optical absorption measurements revealed two optical band gaps (E_g1 and E_g2). The electrical properties were studied using dc electrical conductivity. The filling level (FL) dependency of E_g1 and E_g2, thermal activation energy (ΔE), and hopping distance (R₀) are given to illustrate the behavior of the filled polymers. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 2178–2186, 2004