Electronic Conduction in the Na2O ·nAl2O3–Y2O3 System

The electronic conductivity of Na₂O · nAl₂O₃–Y₂O₃ materials is found to vary from 10^–5 to 10^–1 S/m between room temperature and 800°C and to increase from 10^–5 to 10^–4 S/m as the frequency increases from 100 Hz to 200 kHz. The temperature variation of conductivity is interpreted in terms of the energy band structure.     

Electrical conductivity of iodine adducts of nylon 6 and other non-conjugated polymers

Iodine-nylon 6 adducts containing 70 to 90wt% iodine have been prepared by heating iodine and nylon 6 at 115 and 145° C. The electrical conductivity () of the adduct increases with increase in the iodine content and the iodine-nylon 6 adduct containing 90wt% iodine and prepared at 145° C gives = 10^–3 S cm^–1 at 25° C. Infrared, nuclear magnetic resonance (¹H and¹³C{1 H}), and powder X-ray diffraction analysis of the adduct show a profound change of the structure around the amide group of nylon 6 and suggest the formation of a-C=NH⁺-group in the reaction of nylon 6 with iodine. The temperature dependences of of the idoinenylon 6 adducts prepared at 115° C give activation energies of 51 to 92 kJ mol^–1 depending on the iodine content. Addition of carbon powder to the iodine-nylon 6 adduct causes an increase in electrical conductivity. Other polymers (aliphatic and aromatic nylons, poly(vinyl alcohol), poly (tetrahydrofuran), poly(N-vinylpyrrolidone), poly (4-vi nylpyridine), and poly(acrylonitrile)) which have lone pair or -electrons also form iodine adducts containing 70 to 95 wt % iodine and the adducts show an electrical conductivity in the range of 10^–5 to 10^–2 S cm^–1. Among the iodine adducts, those of poly(vinyl alcohol) and poly (tetra hydrofuran) show electrical conductivities as high as 1.5 X 10^–2 S cm^–1 when the adducts contain about 90 wt% iodine.     

Poly(3-nonylthiophene-co-methylthiophene)s: New soluble conductive copolymers

New conductive soluble copolymers of 3-nonylthiophene (3NT) and 3-methylthiophene (3MT) were chemically synthetized using FeCl₃ in chloroform solution as a catalyst at room temperature and a N₂ atmosphere. The structural properties of the undoped and iodine doped 3NT-co-3MT have been studied by UV-Vis, FTIR, 1H- and ¹³C-NMR, GPC, DSC, TGA, WAXD, magnetic susceptibility and charge transfer measurements. The results show that copolymers (3NT-co-3MT) have a random arrangement. These copolymers have good thermal stability dependent on the 3NT. 3MT content and low magnetic susceptibility (typical for compounds of this class) which decreases with increasing temperature. The conductivity of the iodine doped copolymer (3NT-co-3MT) (measured in the dark at room temperature) increases distinctly in comparison to the undoped samples (2–8×10^–9 Sm^–1).     

Proton Conductivity of Cs2MnH3(P2O7)2 and Rb2MnHP2O7(H2PO4)2

Cs₂MnH₃(P₂O₇)₂ and Rb₂MnHP₂O₇(H₂PO₄)₂ are shown to have an appreciable proton conductivity: 5 × 10^–8 and 2 × 10^–5 S/cm in the Cs compound at 298 and 400 K, respectively, and 10^–7 and 4 × 10^–7 S/cm in the Rb compound. The conductivity and structural data are analyzed in relation to the mechanisms of protonic conduction in these mixed phosphates.     

Fast Li+ ion conduction in Li2O–(Al2O3 Ga22O3)–TiO2–P2O5 glass–ceramics

Fast lithium ionic conducting glass-ceramics have been obtained by heat-treatment of glasses in the systems Li₂O–M₂O₃–TiO₂–P₂O₅ (M = Al and Ga). The glass–ceramics were mainly composed of LiTi₂(PO₄)₃ in which Ti⁴⁺ ions were partially replaced by M³⁺ ions. Considerable enhancement of the conductivity with the substitution of M³⁺ ions for Ti⁴⁺ ions was observed. The maximum conductivity obtained at room temperature was 1.3 × 10^–3 S cm^–1 for the aluminium system and 9 × 10^–4 S cm^–1 for the gallium system.     

Small polaron transport in V2O5–NiO–TeO2 glasses

Semiconducting glasses of the V₂O₅–NiO–TeO₂ system were prepared by the press-quenching method and their d.c. conductivities in the temperature range 300–450 K were measured. The d.c. conductivities at 395 K for the present glasses were determined to be 10^–7 to 10^–1 S m^–1, indicating that the conductivity increased with increasing V₂O₅ concentration. A glass of composition 67.5V₂O₅–2.5NiO–30TeO₂ (mol %) having a conductivity of 2.47×10^–2 S m^–1 at a temperature of 395 K was found to be the most conductive glass among the vanadium-tellurite glasses. From the conductivity–temperature relation, it was found that a small polaron hopping model was applicable at the temperature above _D/2 (_D: the Debye temperature); the electrical conduction at T>_D/2 was due to adiabatic small polaron hopping of electrons between vanadium ions. The polaron bandwidth ranged from 0.06 to 0.21 eV. The hopping carrier mobility varied from 1.1×10^–7 to 5.48×10^–5 cm² V^–1 s^–1 at 400 K. The carrier density is evaluated to be 1.85×10¹⁹–5.50×10¹⁹ cm^–3. The conductivity of the present glasses was primarily determined by hopping carrier mobility. In the low-temperature (below _D/2) regime, however, both Mott's variable-range hopping and Greaves intermediate range hopping models are found to be applicable.     

Chitosan-based electrolyte for secondary lithium cells

The system chitosan : ethylene carbonate : LiCF₃SO₃ was prepared by the solution cast technique. To verify that the conductivity of the material is due to the salt, the electrical conductivity at room temperature of the chitosan acetate film and that of the chitosan acetate films containing different amounts of ethylene carbonate added to it were measured. The order of magnitude of the electrical conductivity was 10^–10 S cm^–1. Films containing fixed content of chitosan and plasticizer but different amounts of salt were then prepared in the same manner and the highest electrical conductivity obtained was 1.3 × 10^–5 S cm^–1 at room temperature. These results indicate that the conductivity is due to the salt. Conductivity-temperature studies show that the ln T versus 10³/T graphs obey Arrhenius rule implying that the conductivity occurs by way of some thermally assisted mechanism. Polarization current measurement shows that the lithium ion transference number is 0.09. A LiMn₂O₄/chitosan-LiCF₃SO₃/C cell was fabricated which cycled between 1.5 to 2.5 V with fading capacity. This could be the result of LiF formation due to interaction between the salt and the fluorine in the binding agent.     

Polyaniline films deposited by anodic polymerization: Properties and applications to chemical sensing

Polyaniline conductive thin films have been used for the detection of a number of important gases and vapors: organic solvents, ammonia, oxygen, hydrogen sulfide, nitrogen and sulfur oxides. The films can be produced by spin coating, thermal evaporation, the Langmuir–Blodgett technique and cyclic voltammetry. This paper presents preliminary results on acidity sensing with electrodeposited polyaniline layers. Polyaniline conductive thin films were prepared by anodic polymerization from an acidic solution of the monomer on two kinds of substrates: gold plated silicon and indium-tin oxide on glass. Ultraviolet-visible (UV-VIS) spectrometry of layers showed a maximum absorption peak around 800 nm for all the samples investigated (independent of preparation conditions) and revealed that the polymeric films were in the emeraldine base form, 18–25% protonated. The room-temperature in-plane d.c. conductivities of the polymer films were found to be between 4×10^–9 S cm^–1 and 9×10^–10 S cm^–1 (deposition rate approximately 4 m h^–1; film thickness 750–1100 nm). Immersion of the polyaniline films in dilute hydrochloric solution resulted in changes in the d.c. conductivity by up to nine orders of magnitude, reaching a value of 4×10^–2 S cm^–1 while immersed in the acidic solution. Humidity tests carried out by exposing polyaniline samples to water vapors changed the d.c. conductivity by one order of magnitude to 1.34×10^–8 S cm^–1.     

Preparation and characterization of plasticized polymer electrolytes based on the PVdF-HFP copolymer for lithium/sulfur battery

PVdF-TG-LiX polymer electrolytes comprised of polyvinylidene fluoride (PVdF)-hexafluoropropylene (HFP) copolymer, tetra(ethylene glycol) dimethyl ether as plasticizer, LiCF₃SO₃, LiBF₄ and LiPF₆ as lithium salt and acetone as solvent have been prepared by solvent casting of slurry that mixed PVdF-HFP copolymer with acetone and salt using a ball-milling technique, which was performed for 2 and 12 h with a ball-to-material ratio of 400:1, and their electrochemical and thermal properties were studied. The ball-milled PVdF-TG-LiX polymer electrolytes have higher ionic conductivity as well as lower glass transition temperature and melting points than the magnetically stirred one. The PVdF-TG-LiPF₆ polymer electrolytes prepared by ball-milling, for, 12 h, in particular, resulted in a maximum value in the ionic conductivity, which was 4.99×10^–4 S cm^–1 at room temperature. The ball-milled PVdF-TG-LiX polymer electrolytes were introduced into Li/S cells with sulfur as cathode and lithium as the anode. The first specific discharge capacities with discharge rate of 0.14 mA cm^–2 at room temperature were about 575 and 765 mA h g–cathode^–1 for magnetic stirring and 12 h ball milling.     

Electrical conductivity of calcium phosphate ceramics with various Ca/P ratios

Calcium orthophosphate powders with various Ca/P ratios were prepared by a wet process, employing CaCO₃ and H₃PO₄ as starting materials. After they were calcined and pressed to form pellets, they were fired at various temperatures ranging from 800 to 1200 °C. The samples at various stages were examined by X-ray diffraction and SEM, The a.c. electrical conductivity was measured for a series of samples. For some of the samples, the d.c. electrical conductivity and electromotive force were also measured. The samples showed relatively high conductivity (4×10^–5 S cm^–1 at 800 °C). With respect to the tricalcium orthophosphate with nearly stoichiometric composition, the predominant charge carrier at 800 °C was presumed to be an ion although it is not identified at the moment.     

Studies on some properties of pristine and iodine-doped poly(phenylene sulphide)

Some properties of poly(phenylene sulphide) prepared by direct synthesis from benzene and sulphur are discussed in the light of thermal analysis, X-ray, SEM, and infrared data. Pristine poly(phenylene sulphide) is characterized by great thermal stability; it loses only 22.5% of its mass during dynamic heating to 873 K. Mass loss for iodine-doped samples increases to 41% depending on the iodine content. Doping with iodine also changes crystallinity, morphology and brings about a rise of electrical conductivity by several orders of magnitude. A conductivity of 1.45 × 10^–2 S m^–1 was obtained in air at room temperature for the poly(phenylene sulphide) sample containing 22.6% iodine.     

A study of the crystallization process of Na1.6Zn0.8Si1.2O4 glass and the ionic conductivity properties of partially crystallized samples

The crystallization process of Na_1.6Zn_0.8Si_1.2O₄ glass was studied by means of differential scanning calorimetry, X-ray powder diffraction and the platinum/carbon replication technique. Partially crystallized samples were made by rapidly cooling samples from elevated temperatures using the DSC apparatus, and the ionic conductivity of the materials was determined by means of impedance measurements conducted at lower temperatures where the crystallization rate was negligible. The glass was found to crystallize at 830 K by precipitation and three-dimensional grain-growth of a crystobalite-type phase with the same composition as the glass. The overall activation energy for the crystallization process was determined from isothermal DSC measurements to be 340 kJ mol^–1. The bulk ionic conductivity for partially crystallized samples increases smoothly from 9.3 x 10^–5( cm)^–1 at 600 K for the glass to 2.4 x 10^–3( cm)^–1 for the crystallized material.     

Electrical properties of Li2O-La2O3-SiO2 electrode glasses after Ta2O5 doping and Ta implantation

Electrical conductivities, , of the Li₂O-La₂O₃-SiO₂ glasses were investigated as functions of Ta₂O₅ doping and Ta ion-implantation. A linear relationship between logarithm and the inverse of the sample temperature, T, was found in 2 to 4 mol% Ta₂O5 doped Li₂O-La₂O₃-SiO₂ glasses. The conductivity increases as Ta₂O₅ content increases at sample temperatures above 100°C. Fluences of 50 keV Ta ions per cm² from 5 × 10¹⁶ to 2 × 10¹⁷ were implanted into 0% and 2% Ta₂O₅ containing Li₂O-La₂O₃-SiO₂ glass samples. The activation energy of the conductivity was deduced from the relation between log and 1/T. It was found in implanted samples that the conductivity increased, but the activation energy and T _k–100 decreased, where T _k–100 is the sample temperature when the conductivity reaches 100 × 10^–1 S/cm. However, the Ta₂O₅ containing implanted samples show higher conductivities, lower activation energies and lower T _k–100. X-ray photoelectron spectroscopy (XPS) was used to study the structural modification introduced by implantation. Bridging oxygen (BO) and non-bridging oxygen (NBO), were observed in all samples. The changes in relative concentrations of BO and NBO before and after implantation clearly indicate the structure modification which results in the increase of the conductivity. It was clearly demonstrated in this study that both doping Ta₂O₅ and implanting Ta ions enhance the conductivity of Li₂O-La₂O₃-SiO₂ electrode glasses.     

D. C. electrical properties of hot-pressed nitrogen ceramics

The d.c. electrical properties of some hot-pressed polycrystalline nitrogen ceramics have been measured between 18 and 500° C in applied electric fields up to 1.1×10⁴ Vcm^–1. The materials examined were Si₃N₄, 5wt%, MgO/Si₃N₄ and two sialons havingz=3.2 andz=4.0. The conduction in all the materials showed similar general features. The time dependent charging (I _c) and discharging currents (I _D) were observed which followed a I(t)t_–n law at room temperature withn=0.7 to 0.8. The exponentn forI _c decreased with increasing temperature. The current density-field (J _s-E) characteristics were ohmic in applied fields of less than 3×10³ Vcm^–1; conductivity increased with electric field above that range. Above about 280° C, a was independent ofE, its temperature dependence following log T ^–1. Below about 230° C conductivity fitted a exp (–B/T _1/4) law in both low and high fields. There is a good correlation between the temperature and field variations of time dependent current and the steady current. The conductivities were in the range of 10^–15 to 10^–16–1 cm^–1 at 18° C and rose to 4×10^–10 to 2×10^{–12 –1} cm^–1 at 500° C. The activation energies were in the range of 1.45 to 1.80 eV and 0.05 to 0.15 eV at above 300° C and near room temperature respectively. Various models to explain the data are considered.     

Preparation, characterization and conductivity studies of AgI-Ag2O-(TeO2 + P2O5) fast ionic conducting glasses

Silverphosphotellurate (SPT) quaternary fast ionic conducting (FIC) glasses of compositions AgI-Ag₂O-[(1 – x)P₂O₅ + xTeO₂], x = 0.0 to 1.0 in steps of 0.1, were prepared by melt quenching. All SPT compounds were characterized by X-ray diffraction and the amorphous nature of the samples was confirmed. The structure of all compositions was examined by Fourier Transform Infrared Spectroscopy. The glass transition temperature (T _g) was determined for all SPT samples, using differential scanning calorimetry. Complex impedance measurements were made on all glasses in the frequency range 40 Hz to 100 kHz. Impedance data were analyzed using Boukamp equivalent circuit software and the bulk conductivity was obtained. The highest conductivity ( = 1.59*10^–2 S/cm) was shown by the composition 60%AgI – 26.67%Ag₂O – 13.33% (0.3P₂O₅ + 0.7TeO₂).     

Morphology and ionic conductivity of solid polymer electrolytes based on polyurethanes with various topological structures

Polyurethanes with linear, hyperbranched and comb-crosslinked structures were synthesized and were used to prepare solid polymer electrolytes. The polymer electrolytes were characterized by means of Fourier transform Raman spectroscopy, impedance spectroscopy (IS) and atomic force microscopy (AFM). The results showed that salt concentration significantly influences the morphology and conductivity of the three kinds of polyurethane/LiClO₄ system. When the mole ratios of the ether oxygen atom to lithium ion were controlled to be 12, 4 and 4 respectively for linear, hyperbranched and comb cross-linking polyurethane, the electrolytes typically displayed micro-phase separated morphology and the ionic conductivity also reached maxima respectively at 2.2 × 10^–7 S/cm, 2.8 × 10^–6 S/cm and 2.8 × 10^–5 S/cm at room temperature.     

Synthesis and thermoelectric characterization of polycrystalline Ni1−x Ca x Co2O4 (x=0–0.05) spinel materials

Ca doped NiCo₂O₄ spinel materials were synthesized by conventional solid state reactions at 900 °C. Thermoelectric properties of polycrystalline products were characterized at high temperature range of 800 °C in air. d.c. conductivity of the prepared polycrystalline 5 mol % Ca doped NiCo₂O₄ was about 60 S m^–1 at 300 °C. The value of d.c. conductivity was increased with the temperature increasing. Thermoelectric voltage of polycrystalline Ni_1–x Ca _x Co₂O₄ (x=0–0.05) was positive at 300–800 °C, this showed p-type thermoelectric properties. The Seebeck coefficient of 5 mol % Ca doped NiCo₂O₄ was ca. 300 V/K at 600 °C. The value of the Seebeck coefficient of Ni_1–x Ca _x Co₂O₄ polycrystalline products decreased with the increasing temperature. Thermal conductivity of 5 mol % Ca doped NiCo₂O₄ was ca. 2.2 W m^–1 K^–1 at 600 °C. The estimated thermoelectric figure-of-merit, Z, of 5 mol % Ca doped NiCo₂O₄ spinel polycrystalline product was about 3.5×10^–5 K^–1 at 600 °C.     

Magnetic properties of hydrothermally synthesized strontium hexaferrite as a function of synthesis conditions

Fine particles of strontium hexaferrite, SrFe₁₂O₁₉, with a narrow size distribution have been synthesized hydrothermally from mixed aqueous solutions of iron and strontium nitrates under different synthesis conditions. The relationship between the synthesis variables (temperature, time and alkali molar ratio) and the magnetic properties has been investigated. The results have shown that, as the synthesis temperature increases, the saturation magnetization of the particles increases up to a plateau and the coercivity decreases. As the alkali molar ratio R(=OH^–/NO ₃ ^– ) increases, the coercivity decreases and goes through a local minimum, while the saturation magnetization increases and goes through a local maximum. Increasing the synthesis time from 2 h to 5 h has no significant effect on the saturation magnetization, but decreases the coercivity. An anisotropic sintered magnet with a high saturation magnetization value of 67.26 e.m.u g^–1 (4320 G) has been fabricated from the hydrothermally synthesized powders.Relationship between the c.g.s and S.I.units which are used in this paper are as follows: 1 erg = 10^–7 J, 1 e.m.u. cm^–3 = 12.57×10^–7 Wom^–2 (tesla), 1 oersted (Oe) = 79.6 A m^–1, 1 G = 10^–4 tesla (T).     

Electrical and optical properties of r.f.-sputtered amorphous V2O5-CaO-MoO3 films

Amorphous films of the V₂O₅-CaO-MoO₃ system are fabricated by r.f.-sputtering and the d.c. conductivity and optical properties are studied. The conductivity of 1200–1400 nm thick amorphous V₂O₅-CaO-MoO₃ films with different film compositions ranges from 4.7 × 10^–4 to 1.1 S cm^–1 at 458 K. The films are n-type semiconducting. The conduction of the films is attributed to adiabatic small polaron hopping and is primarily due to hopping between V⁴⁺ and V⁵⁺ ions. The films are optically transparent in the visible range. The optical band gap energy is evaluated to be between 2.90 and 2.39 eV. The Urbach tail analysis gives the width of localized states between 0.40 and 0.58 eV. A feasibility study reveals the films to be applicable as transparent film thermistors.     

Crystallisation of selenium thin films doped with iodine after evaporation

Amorphous selenium thin films deposited under vacuum have been doped with iodine either during or after crystallisation. It is shown that when the films are first crystallised at 363 K for 6 h and then submitted to iodine atmosphere at 363 K for 1 h, the structural properties of the films are not modified while their conductivity increases by a factor of 8. Iodine atmosphere induces post crystallisation of amorphous selenium films even at room temperature by increasing the selenium atom mobility at the surface of the films, which induces growth of crystalline spherulites. With annealing, when the heating rate is high (>15 K/min), constraints appear in the films, the density of spherulites increases and the films are inhomogeneous. When the heating rate is small and constant (1 K/min) the interaction between iodine and selenium takes place all over the sample and there is only a small density of small spherulites, while the crystallisation of the whole sample is more homogeneous. XPS and microprobe analysis that the iodine is equally repartitioned in the selenium film show it. Moreover there is a mixture of neutral iodine andS I₃ ^– as shown by XPS and Raman studies. The high crystalline quality of the films can explain the high conductivity (>10^{–3 –1} cm^–1) of these selenium doped films