Theoretical study on the co-crystal composed of poly(diiododiacetylene) and bis(nitrile) oxalamide

The binding details and electronic properties of the co-crystal composed of poly(diiododiacetylene) and bis(nitrile) oxalamide are investigated using self-consistent field crystal orbital method. It is found that the cooperative effects exist in the stack of bis(nitrile) oxalamides and the hydrogen bond interaction between bis(nitrile) oxalamides plays an important role in the stability of the co-crystal. The calculated band structures show that the co-crystal is a semiconductor and the poly(diiododiacetylene) can be considered as a quasi one-dimensional chain. The calculated mobility for the one-dimensional poly(diiododiacetylene) chain has the order of 10³ cm² V⁻¹ s⁻¹.     

Ionic conductivity and electrochemical stability of poly(methylmethacrylate)-poly(ethylene oxide) blend-ceramic fillers composites

The role of inorganic ceramic fillers namely nanosized Al₂O₃ (15-25 nm) and TiO₂ (10-14 nm) and ferroelectric filler SrBi₄Ti₄O₁₅ (SBT CIT) (0.5 μm) synthesized by citrate gel technique (CIT) on the ionic conductivity and electrochemical properties of polymer blend 15 wt% PMMA+PEO₈:LiClO₄+2 wt% EC/PC electrolytes were investigated. Enhancement in conductivity was obtained with a maximum of 0.72×10⁻⁵ S cm⁻¹ at 21 °C for 2 wt% of SrBi₄Ti₄O₁₅ (SBT CIT) composite polymer electrolyte. The lithium-ion transport number and the electrochemical stability of the composite polymer electrolytes at ambient temperature were analyzed. An enhancement in electrochemical stability was observed for polymer composites containing 2 wt% of SrBi₄Ti₄O₁₅ (SBT CIT) as fillers.     

Localized and long-distance charge hopping in fresh and thermally aged conductive copolymers of polypyrrole and polyaniline studied by combined TSDC and dc conductivity

The charge trapping centers in fresh and thermally aged conductive polyaniline-polypyrrole copolymers (starting from pure polyaniline and ending in pure polypyrrole by steps of 10 wt%) were studied by thermally stimulated depolarization current (TSDC) spectroscopy and dc conductivity measurements. One low temperature (115-135 K) relaxation mechanism appears in polyaniline-rich copolymers and disappears after thermal anneal. It is attributed to polaron trapping in the vicinity of chlorine anion dopants. Another relaxation mechanism operates close to room temperature and is related to conformational relaxation, which corresponds to the influence of the annihilation of the conformons on the conduction mechanism. The relaxation is sensitive to thermal aging as a result of the thermal annealing on the conductivity. The temperature derivative of the dc conductivity supports the latter assertion. The activation energy values were obtained as a function of composition for both fresh and heated samples. The TSDC spectroscopy is a sensitive tool which is an alternative to the standard conductivity studies for the characterization of polypyrrole-polyaniline conductive copolymers and the study of the thermal degradation.     

Synthesis and application of the solar cell of poly(3-hexylthiophene)/Fe N/titanium dioxide nanocomposite material

A series of nanocomposites of poly(3-hexylthiophene) with Fe N-doped TiO₂ (P3HT/Fe N/TiO₂) were synthesized by the chemical method in situ. The structure of the prepared composites was characterized using X-ray diffraction patterns (XRD), infrared spectroscopy (IR), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). Optical and electrochemical properties were determined using UV-vis spectroscopy, fluorescence spectroscopy, and cyclic voltammetry. These tests indicated that P3HT/Fe N/TiO₂ is a new p-n semiconductor. Two solar cells based on P3HT/Fe N/TiO₂ were manufactured and studied.     

Dielectric properties and fluctuating relaxation processes of poly(methyl methacrylate) based polymeric nanocomposite electrolytes

Solid polymer nanocomposite electrolytes (SPNEs) consisted of poly(methyl methacrylate) (PMMA) and lithium perchlorate (LiClO₄) of molar ratio C=O:Li⁺=4:1 with varying concentration of montmorillonite (MMT) clay as nanofiller have been prepared by classical solution casting and high intensity ultrasonic assisted solution casting methods. The dielectric/electrical dispersion behaviour of these electrolytes was studied by dielectric relaxation spectroscopy at ambient temperature. The dielectric loss tangent and electric modulus spectra have been analyzed for relaxation processes corresponding to the side groups rotation and the segmental motion of PMMA chain, which confirm their fluctuating behaviour with the sample preparation methods and also with change of MMT concentration. The feasibility of these relaxation fluctuations has been explained using a transient complex structural model based on Lewis acid–base interactions. The low permittivity and moderate dc ionic conductivity at ambient temperature suggest the suitability of these electrolytes in fabrication of ion conducting electrochromic devices and lithium ion batteries. The amorphous behaviour and the exfoliated/intercalated MMT structures of these nanocomposite electrolytes were confirmed by X-ray diffraction measurements.     

Preparation of highly conductive CNTs/polyaniline composites through plasma pretreating and in-situ polymerization

In this study, carbon nanotubes (CNTs) were pretreated by plasma, and further in-situ polymerized with aniline to achieve uniform CNTs/polyaniline (PANI) composites with high conductivity. The highest conductivity (2.946 S/cm) of CNTs/PANI composites under optimum plasma treating parameters is much higher than those without CNTs pretreatment or premodified by acid oxidation method. The scanning electronic microscope (SEM) pictures indicate that smooth surfaces of pristine CNTs (diameter: 20-40 nm) changes into rough structures and the size increases to around 90 nm, which is further proved by the X-ray diffraction (XRD), the Fourier transform infrared spectroscopy (FTIR), and the Raman measurements. Thermogravimetric analysis (TGA) results reveal that the thermal stability of CNTs/PANI composite is better than that of pure PANI.     

Metal-insulator transition and variable-range hopping conductivity of n-CdSb in magnetic field

Resistivity, ρ, of a II-V group semiconductor n-CdSb doped with In is investigated in pulsed magnetic fields up to and at temperatures . The low-temperature resistivity ρ(T) increasing with T in the range of B<4 T is found to have an upturn around B∼4 T and strong activated behavior at further increase of B. These observations give evidence for magnetic-field-induced metal-insulator transition (MIT). In the insulating side of the MIT, Mott variable-range hopping (VRH) conductivity with two types of asymptotic behavior, ln ρ (T, B)∼T^−3/4B² and ln ρ (T, B)∼(B/T)^1/3, is established in low and high magnetic fields, respectively. The VRH conductivity is analyzed using a model of the near-edge electron energy spectrum established by investigations of the Hall effect. The VRH conductivity is shown to take place over the band tail states of one out of two impurity bands, which for T=0 and B=0 lie above the conduction band edge.     

Preparation and characterization of carbon nanotubes/epoxy resin nano-prepreg for nanocomposites

The surface carbon nanotubes (CNTs) were modified to generate functional reactors by using the sonicication method to distribute CNTs evenly among epoxy resin, which was prepared into nano-prepreg with carbon fibers. Additionally, based on various proportions of modified and unmodified CNTs, the mechanical properties and conductivities of the composite, as well as, the characteristics of material subjected to various temperature conditions were investigated. Experimental results indicate that increasing CNT content enhances the mechanical strength and electrical properties. At various temperatures, the mechanical strength drops with increase in temperature because different expansion coefficients differ between fiber and epoxy resin. Finally, the failure surface of nanocomposite was examined using scanning electron microscopy (SEM). Finally we provide a discussion of the failure mechanism of the material.     

Effect of elastomer matrix type on electromechanical response of conductive polypyrrole/elastomer blends

Electrorheological properties of prestine elastomers and polypyrrole/elastomer blends were investigated to identify the most suitable elastomer to be used in electroactive actuator applications. Seven types of elastomer: poly(acrylate) copolymers (AR70, AR71, AR72, and SAR), poly(dimethyl siloxane) (PDMS), poly (styrene butadiene) (SBR), and poly(styrene isoprene styrene) (SIS) were chosen as the candidate dielectric elastomers. For the pure elastomers, the storage modulus responses, ΔG′, amongst the elastomers differ by 6 orders of magnitude at the electric field strength of 2 kV/mm. The storage modulus sensitivity, ΔG′/G′₀, increases with electric field strength and attains maximum values of 97% for SBR, 148% for SAR, 232% for AR70, 13% for PDMS, 69% for AR71, 54% for AR72, and 10% for SIS at the electric field strength of 2 kV/mm. Correlations are identified between the elastomer storage modulus sensitivity and G′₀ and/or electrical conductivity. For the undoped polypyrrole/elastomer blends with the particle concentrations of 1, 2, 3, 4, and 5 vol%, ΔG′ increases linearly with concentration in the absence of electric field but nonlinearly with electric field on, due to the obstruction of the matrix-dipole interaction at small concentrations and the nonuniform polypyrrole particle dispersion in the matrix at high concentrations.     

On the power-law behavior of the AC conductivity of the mixed crystal (NH4)3H(SO4)1.42(SeO4)0.58

A power law used to describe the AC conductivity from 299 to 393 K of the mixed crystal (NH₄)₃H(SO₄)_1.42(SeO₄)_0.58 led to fractional exponent values ranging from 1.08 to 0.91, depending on structural changes induced on temperature variation [B. Louati, M. Gargouri, K. Guidara and T. Mhiri, J. Phys. Chem. Solids 66 (2005) 762]. In the present note, we suggest that the fractional law exhibits features of lattice relaxation. Despite the structural changes, the parameters of the power law are mutually interconnected to yield a temperature independent phenomenon. Such behavior is probably of general validity and characterizes the universal fractional dispersion of the AC conductivity, as it was also observed in glasses of different composition.     

Defect structure and electrical properties of molybdenum disulphide

Electrical conductivity of molybdenum disulphide was studied in a helium-sulphur gas mixture as a function of temperature (1073-1273 K). It was found that over the whole temperature and sulphur pressure range (10-6600 Pa) studied, the material exhibits p-type conductivity. Based on literature intrinsic electronic disorder data as well as measured electrical conductivity results a defect model has been proposed. This model involves electron holes and doubly ionized interstitial sulphur ions as majority point defects as well as electrons and acceptor-type foreign ions as minority defects.     

Temperature dependence of thermoelectric properties of Ni-doped CoSb3

Temperature dependences of the Hall coefficient, Hall mobility and thermoelectric properties of Ni-doped CoSb₃ have been characterized over the temperature range from 20 to 773 K. Ni-doped CoSb₃ is an n-type semiconductor and the conduction type changes from n-type to p-type at around 450 K. The temperature for the transition from n-type to p-type increased with increasing Ni content x. The Seebeck coefficient reaches a maximum value near the transition temperature. The electrical resistivity indicates that Co_1−xNi_xSb₃ is a typical semiconductor when x≤0.03 and a degenerate semiconductor when x>0.03. Thermal conductivity analyses show that the lattice component is predominant at lower temperatures and carrier and bipolar components become large at temperatures higher than the transition temperature. The thermoelectric figure of merit reaches a maximum value close to the transition temperature and the largest value, 4.67×10⁻⁴ K⁻¹ at 600 K, was obtained for x=0.05.     

Galvanomagnetic properties of air-stable and highly conductive potassium-intercalated graphite sheet

Magnetoresistance and Hall coefficient of air-stable potassium-intercalated graphite sheets (hereafter abbreviated as K-PGS) were determined at room temperature. The magnitude of the magnetoresistance and the absolute value of Hall coefficient of K-PGS decreased with increasing potassium content of K-PGS, n_K/n_C. Two-carrier model was used for calculating carrier density and mobility. The electron density increased with increasing n_K/n_C: 3.07×10²⁰ cm⁻³ (n_K/n_C=0.005), 5.67×10²⁰ cm⁻³ (n_K/n_C=0.008) and 6.40×10²⁰ cm⁻³ (n_K/n_C=0.011). The value of the electron density of K-PGS with n_K/n_C=0.011 (nominal composition KC₉₁) was about 80% of the reported value, 7.8×10²⁰ cm⁻³, for KC₄₈ (n_K/n_C=0.021) prepared from HOPG (highly oriented pyrolytic graphite). The mobility decreased with increasing n_K/n_C: 2.11×10³ cm² V⁻¹ s⁻¹ (n_K/n_C=0.005), 1.42×10³ cm² V⁻¹ s⁻¹ (n_K/n_C=0.008) and 1.34×10³ cm² V⁻¹ s⁻¹ (n_K/n_C=0.011). The value of the mobility of K-PGS with n_K/n_C=0.011 was about 60% of the reported value (2300 cm² V⁻¹ s⁻¹) for KC₄₈ prepared from HOPG.     

Electrospun nanofibers of poly(ethylene oxide)/teraamino-phthalocyanine copper(II) hybrids and its photoluminescence properties

Poly(ethylene oxide)/teraamino-phthalocyanine copper (II) (PEO/(NH₂)₄PcCu) hybrid nanofibers with a diameter of 200-300 nm were prepared by electrospinning technique. The hybrid nanofibers membrane was characterized by scanning electron microscopy (SEM), Fourier transform infrared (FT-IR), ultraviolet-visible (UV-vis), and photoluminescence (PL), respectively. The results indicated that (NH₂)₄PcCu molecule was successfully embedded in the one-dimensional hybrid nanofibers via chemical interaction between PEO and (NH₂)₄PcCu. The PL results showed that the PEO/(NH₂)₄PcCu hybrid nanofibers had an intense emission at about 450 nm. A possible PL mechanism was proposed accordingly.     

Optical, electrical and photovoltaic properties of thermally annealed PPHT:DDE blend thin films

We have investigated the optical, electrical and photovoltaic properties of devices based on 1,2-diazoamino diphenyl ethane (DDE) and poly(3-phenyl hydrazone thiophene) (PPHT):DDE blend. It is observed from the J-V characteristics of the Al/DDE/ITO (ITO—indium tin oxide) device that the electron current injected from Al contact was shown to be space charge limited (SCL), indicating that Al forms nearly ohmic contact for electron injection into lowest unoccupied molecular orbital (LUMO) of DDE. The effect of thermal annealing and composition, on the optical, electrical and photovoltaic response of blend of PPHT and DDE sandwiched between a transparent ITO electrode and an Al back contact are investigated. The observed absorption quenching in the PPHT:DDE blend is attributed to the disordering of PPHT chains and charge transfer between PPHT and DDE as evidenced by FTIR spectra. The observed red shift in the absorption peak on thermal annealing is due to the improvement in the ordering and increases in conjugation length in PPHT. The observed dark current-voltage curves agree well with trap-controlled SCL transport theory. The photophysics of the blend material and influence of thermal annealing on the performance and morphology of these devices were discussed. Annealing process results in the formation of PPHT:DDE complex and increase in the ordering of polymer chain, that increases the incident photon to current efficiency (IPCE) and power conversion efficiency of the photovoltaic devices.     

Low temperature thermoelectric properties of Pb- or Sn-doped Bi-Sb alloys

Pb- or Sn-doped Bi₈₈Sb₁₂ alloys were prepared by direct melting, quenching, and annealing. The Bi-Sb alloy phase was predominant in all samples. Pb or Sn atoms were distributed almost uniformly in Bi₈₈Sb_12, while some segregation was confirmed at the grain boundaries when Pb or Sn was involved heavily. The thermoelectric properties of these doped materials were investigated by measuring the Hall coefficient, electrical resistivity, and Seebeck coefficient between 20 K and 300 K. The Hall and Seebeck coefficients of Pb- or Sn-doped samples were positive at low temperatures, indicating that the doping element acted as an acceptor. Temperatures resulting in positive Hall and Seebeck coefficients further increased with increasing doping amount and with respect to the annealing process. As a result, a large power factor of 1.2 W/mK² could be obtained in the 3-at% Sn-doped sample at 220 K, with a large positive Seebeck coefficient.     

Hopping type of conduction in (Na0.5Bi0.5)ZrO3 ceramic

Polycrystalline sample with (Na_0.5Bi_0.5)ZrO₃ (NBZ) stoichiometry was prepared using a high-temperature solid-state reaction technique. X-ray diffraction (XRD) analyses indicate the formation of a single-phase perovskite-type orthorhombic structure. AC impedance plot is used as tool to analyse the electrical behaviour of the sample as a function of temperature at different frequency. The AC impedance studies revealed the presence of grain boundary effect and evidence of a negative temperature coefficient of resistance (NTCR) character. Pseudo Cole-Cole and complex electric modulus analyses indicated non-Debye-type dielectric relaxation. The AC conductivity obeys the universal power law. The pair approximation type correlated barrier hopping (CBH) model explains the universal behaviour of the s exponent. The apparent activation energy to the conduction process and minimum hopping distance are discussed.     

Preparation of alkaline solid polymer electrolyte based on PVA-TiO2-KOH-H2O and its performance in Zn-Ni battery

A novel composite alkaline polymer electrolyte based on poly(vinyl alcohol) (PVA) polymer matrix, titanium dioxide (TiO₂) ceramic fillers, KOH, and H₂O was prepared by a solution casting method. The properties of PVA-TiO₂-KOH alkaline polymer electrolyte films were studied by X-ray diffraction (XRD), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), and AC impedance techniques. DSC and XRD results showed that the domain of amorphous region in the PVA polymer matrix augmented when TiO₂ filler was added. The SEM result showed that TiO₂ particles dispersed into the PVA matrix although some TiO₂ aggregates of several micrometers were formed. The alkaline polymer electrolyte showed excellent electrochemical properties. The room temperature (20 °C) ionic conductivity values of typical samples were between 0.102 and 0.171 S cm⁻¹. The Zn-Ni secondary battery with the alkaline polymer electrolyte PVA-TiO₂-KOH had excellent electrochemical property at the low charge-discharge rate.     

Electrical conductivity of (Er,U)O2+x and (Ce,U)O2+x

The electrical conductivity (σ) of (Er_yU_1−y)O_2+x (y=0.06, 0.20) and (Ce_yU_1−y)O_2+x (y=0.05, 0.15, 0.25) has been measured as a function of oxygen partial pressure in the temperature range of 1100≤T/°C≤1300 by a d.c. 4-probe method. Both of the oxides exhibited Po₂-regions where the electrical conductivity is independent of oxygen partial pressure, which indicates that doped Er and Ce exist as trivalent cations on uranium sites and fix the hole concentration by acting as electron acceptors, i.e. [h]=[Er′_U] and [h]=[Ce′_U], respectively. It is considered that strong oxidization tendency of uranium and reduction tendency of cerium simultaneously render the cerium ions exist exclusively as Ce³⁺ in the uranium dioxide. The electron-hole mobility of (Er_yU_1−y)O_2+x and (Ce_yU_1−y)O_2+x in the Po₂ region where σ is constant has been calculated by the combination of the electrical conductivity and charge carrier concentration; the activation energy (E_H) of each oxide has been obtained from the temperature dependence of the mobility. Small polaron hopping conduction mechanism was confirmed by small magnitude of the mobility (0.018-0.052 cm² V⁻¹ s⁻¹) and the activation energy (0.12-0.22 eV).     

Crystallinity and dielectric relaxations in semi-crystalline poly(ether ether ketone)

The Maxwell-Wagner-Sillars (MWS) relaxation is studied for semi-crystalline polymers poly (ether ether ketone) (PEEK), in the range 20 Hz-1 MHz and temperature varying from 80 to 330 °C. The parameter is the crystallization condition in the case of PEEK, which is a semi-crystalline polymer considered as a particulate composite. The relaxation found in the semi-crystalline polymers above the α relaxation of the PEEK is ascribed to the trapping of conductive carriers at the interface between crystalline lamellae and the amorphous matrix. The study of PEEK microstructure is based on differential calorimetry and X-rays diffraction. Two lamellae populations have been detected, that depends on the crystallization temperature and its duration. The crystallinity rate is increasing with crystallization temperature and duration. In dielectric studies, the use of the electric modulus instead of permittivity allows us to minimize the ionic conduction and then leads to the appearance of the interfacial relaxation. According to our measurements, the crystallinity rate is not the main factor of the interfacial relaxation intensity, which also depends on the nature and degree of perfection of the lamellae.