Synthesis and electrical properties of poly(p-azoarylene) films

Polymers and copolymers containing p-azoarylene and p-azoxyarylene groups were synthesized by oxidative coupling of various aromatic diamines. Films were cast directly from the reaction mixtures or from the polymer solutions. The films were n-doped by sodium naphthalide or p-doped by iodine. They showed electrical conductivities of 10⁻⁴ ohm⁻¹ cm⁻¹ to 10⁻⁵ ohm⁻¹ cm⁻¹.     

Study of IF5 chemical doping of aluminium polyfluorophthalocyanine: (PcAlF)n

Chemical IF₅ doping of aluminium polyfluorophthalocyanine, (PcAlF)_n, has been studied by thermogravimetric analysis, infrared spectroscopy, elemental analysis and electrical conductivity measurements. An optimum electrical conductivity (σ = 6 × 10⁻² ω⁻¹ cm⁻¹) is achieved for a doping rate lying in the range 0.5 - 0.8 mole of IF₅ per (PcAlF) ring. The decrease of electrical conductivity of the doped material measured for higher doping rates is shown to be related to the disappearance of the eclipsed configuration in the stacking of the rings, induced by excess inserted dopant species. These results confirm those previously published concerning the AsF₅ doping of the polymer and can be explained with the help of the same structural model.     

Electrically conducting complexes of poly(3,6-N-methylcarbazolyl methylene

Poly(3,6-N-methylcarbazoly methylene) prepared by acid-catalysed condensation polymerization of N-methylcarbazole with formaldehyde exhibits p-type semiconducting properties when doped with electron acceptors such as iodine, bromine, nitrosyl tetrafluoroborate and nitrosyl hexafluoroantimonate. The polymer samples have T_g in the range 100 – 148 °C, chain length in the range 13 – 25, and a molecular weight distribution of 1.17 –1.51. The polymer complexes with dopant anion (I₃^?, Br₃^?, BF₄^?) to polymer repeating unit ratio of 0.67 – 0.95 have a d.c. conductivity of 10^?3 to 10^?1 ohm^?1 cm^?1 and a positive thermoelectric voltage at 23 °C.An important new feature of the methylene-bridged polycarbazole conducting polymers is doping-induced polymer backbone conjugation of the form CH₂→=CH. Evidence for this oxidation mechanism, converting methylene linkage to methine linkages, includes elemental analysis, infrared spectra, proton NMR and electron spin resonance results.     

Investigations in the field of synthetic metals. VI. Synthesis and properties of dibenzotetrathiafulvalene halides

Direct oxidation of dibenzotetrathiafulvalene (DBTTF) by halogens in acetonitrile and nitrobenzene yielded DBTTF₂I₃, DBTTF·I₃, DBTTF·Cl_x (x = 0.7 ? 1), DBTTF·Br_x (x = 0.8 ? 1), and DBTTF·Br_1.2 complexes. Ir-, u.v.-, and e.p.r.-spectra of these compounds have been studied. X-ray data for the complex DBTTF·I₃ are discussed. Conductivities of the above mentioned complexes lie in the range 10^?2 – 10^?4 ohm^?1 cm^?1.     

Experimental studies of n-doped (CH)x: D.c. electrical conductivity

The d.c. electrical conductivity of n-doped (CH)_x was studied as a function of the doping level at 25°C. The dopants were sodium-naphthalene, lithium and sodium benzophenone dianionic salts in tetrahydrofuran (THF). Details of the experimental procedure are described.It was discovered that the THF vapour pressure present in the atmosphere in contact with the doped film drastically increases the film conductivity, at low doping levels. This may be due to an effect of the solvation state of cations.Conductivity measurements were also performed at very low doping levels (evaluated from metallic infrared bands) on (CHNa_y)_s, (CDNa_y)_x and (CDK_y)_x. A mobility value of 4 × 10^?6 cm^2/rmVs was deduced for 57% trans-(CHNiny)_x.     

Resonant Raman spectroscopy of conducting organic polymers. (CH)x,and an oriented analog

The results of low-temperature Raman scattering experiments on cis and trans (CH)_x are reviewed, and the Raman bands corresponding to carbon -carbon stretches of the polymer backbone discussed. The Raman spectra of a variety of commercial polarizing sheet, Polaroid K, are presented. The spectra indicate that the dehydrated polyvinyl alcohol chain in Polaroid K is an oriented analog of trans (CH)_x for purposes of Raman spectroscopy.For films of trans (CH)_x, changes in the Raman profile with excitation wavelength reveal the presence of a distribution of effective chain lengths. The shorter the length of conjugated chain, the higher the carbon-carbon stretch frequencies, and the further to the blue the optical absorption and wavelength necessary for maximum resonant enhancement of the Raman scattering. The shape and positions of the carbon-carbon band corresponding to double bond stretching suggest the presence of lengths of chain (terminated by conjugation or bonding defects) having x (number of monomer units) from x ? 10 to x ? 100. This is based on a limiting C=C frequency in an infinite chain of 1450 cm^?1, determined from the wavelength-independent, low-frequency origin of the band. A similar band-shifting phenomenon in Polaroid K is displayed.Spectra of iodinated (CH)_x and iodinated Polaroid K are presented which suggest a similarity between the dopant species present in the two different materials.     

Preparation and characterization of Mg-doped CaCu3Ti4O12 thin films

Mg-doped CaCu_3?xMg_xTi₄O₁₂ (x=0, 0.05, 0.1, 0.15, 0.2, at.%) thin films were prepared by a modified sol?gel method. A comparative study on the microstructure and electrical properties of Mg-doped CaCu₃Ti₄O₁₂ (CCTO) thin films was carried out. The grain sizes of the Mg-doped CCTO thin films were smaller in comparison to the undoped CCTO films. Furthermore, compared to undoped CCTO films, Mg-doped CCTO thin films obtained higher dielectric constant as well as excellent frequency stability. Meanwhile, Mg doping could reduce the dielectric loss of CCTO thin films in the frequency range of 10⁴?10⁶ Hz. The results showed that the Mg-doped CCTO thin films had the better electrical characteristics compared with the undoped CCTO films. The nonlinear coefficient of Mg-doped CCTO thin films at x=0.15 and x=0.1 was improved to 7.4 and 6.0, respectively.     

Vibrational properties of Li-doped polyacetylene

Raman experiments on (CH)_x chemically doped with Li are reported. A very fast cis-trans isomerization is observed upon doping. Raman spectra of Li-doped cis or trans films show special features characteristic of short trans segments which remain undoped. Further, an additional Raman band at $\text{≌ 1570}\text{cm}{}^{\mathrm{?1}}$ is reported, as in the p-type doping case, associated with doped parts of the polymer. A possible interpretation with intercalated domains is suggested.     

Photoconductivity and function properties of polyacetylene films

Photoconductivity and photovoltaic effects of AsF₅-doped and undoped trans-(CH)_x films have been measured at room temperature in the wavelength region from 0.3 to 3.5 μm. The photovoltaic response threshold at 1.48 eV, measured on Schottky barrier junctions with a low work function metal, is interpreted as the single particle band-gap of trans-(CH)_x. I-V and C-V characteristics of the junctions indicate that good Schottky barriers are formed between lightly doped p-type (CH)_x and low work function metals. Evidence for ～ 2 × 10¹⁸ cm^?3 deep traps in both doped and undoped trans-(CH)_x is obtained from analysis of these characteristics.     

Mechanism of Electrical Conduction in Molten Cu S-Cu Cl and Mattes

The specific conductance and its temperature dependence were measured over the entire composition range of the molten Cu₂S-CuCI system. At a typical temperature of 1200°C, 10 mol pct of the ionically conducting CuCl reduced the specific conductance from about 77 ohm^?1cm^?1 for pure Cu₂S to about 32 ohm^?1cm^?1, and 50 mol pct CuCl reduced the conductance to that for pure CuCl—about 5 ohm^?1cm^?1. The nature of electrical conduction in molten Cu₂S, FeS, CuCl, and mixtures was studied by measuring the current efficiency of electrolysis at about 1100°C. The Cu₂S, FeS, and mattes were found to conduct exclusively by electrons, but addition of 15 wt pct CuS to Cu₂S produces a small amount of electrolysis. Addition of CuCl to Cu₂S suppresses electronic conduction, and ionic conduction reaches almost 100 pct at a CuCl concentration of about 50 mol pct. These facts are interpreted in terms of electron energy level diagrams by analogy to the situation in solids.     

AlCl3-assisted formation of charge-transfer complexes between polyacetylene and tetracyanoethylene,TCNE

Polyacetylene, (CH)_x, the simplest conjugated polymer, can be converted into a conducting materials (8 Ω⁻¹ cm⁻¹) by treating it with TCNE/ AlCl₃/benzene solution. An electron transfer π-complex was obtained, as shown by EPR and XPS spectroscopies.     

Resonant Raman scattering of Er3+ doped and partially isomerized polyacetylene

The results of experimental studies of resonant Raman scattering (RRS) spectra from Er³⁺ implantation doped and partially isomerized polyacetylene are presented. Thin cis-(CH)_x films were synthesized by the method of rare earth complex catalysis polymerization. Doping technique is ion implantation. The surface density of implanted Erbium ion is about 5×10¹³/cm². In the case of cis-(CH)_x, RRS bands at 1160, 1270 and 1540 cm⁻¹ have been observed λ_L = 488 nm (10K) and it was shown clearly that a shift in frequency of the peaks assigned to the remaining trans segments occurs during the isomerization process. In the case of Er³⁺ doped cis-(CH)_x, Er³⁺ induced Raman bands at 1145, 1320 and 1510 cm⁻¹ have been measured (λ_L = 488 nm, RT) for the first time and it is observed that the Raman bands from Er³⁺ doped trans/cis-(CH)_x are shifted to lower frequencies. We point out that the effect of Er³⁺ dopant is associated with the defects.The experimental results are discussed by using the model based on the hypothesis that the sample properties can be interpreted in terms of a bimodal distribution of long and short conjugation length segments (for trans-(CH)_x) and the bipolaron microscopic model on the basis of multi-phonon lattice relaxation theory (for cis-(CH)_x). Our studied results support further the bimodal distribution model and the bipolaron microscopic model.     

In situ conductivity and photoconductivity measurements of polyaniline films

In situ conductivity measurements on a polyaniline film with a fourprobe electrode are performed in NH₄F, 2.3HF and in propylene carbonate in the dark and under illumination. The conductivity is also determined on a pellet of chemically prepared polyaniline mixed with carbon black as for a battery electrode. The upper values of conductivities are 120 ohm⁻¹ cm⁻¹ in the hydrofluoric medium, 25 ohm⁻¹ cm⁻¹ in propylene carbonate and 8 ohm⁻¹ cm⁻¹ in the solid dry state. For a pellet with 20% carbon black it is 0.5 ohm⁻¹ cm⁻¹. The increase in conductivity of the polyaniline film in the solid state upon illumination is about 0.7 ohm⁻¹ cm⁻¹ (10%).     

Study of chemically (AsF5) and electrochemically doped aluminium polyfluorophthalocyanine, (PcAlF)n

Chemical AsF₅ and electrochemical AsF₆^? doping of aluminium polyfluorophthalocyanine, (AlPcF)_n, has been studied. Thermogravimetric analysis, infrared spectroscopy, X-ray diffraction and electrical conductivity measurements were used to characterize the doped materials. Particular attention has been devoted to the study of the most heavily doped samples obtained in the first case (between 4 and 5 AsF₅ molecules per phthalocyanine ring). A qualitative structural model is proposed to explain the low electrical conductivity of these samples. Results are compared with those for iodine-doped (AlPcF)_n and (GaPcF)_n.Cyclic voltammetry performed on polymer films revealed the existence of two oxidation peaks. While it is very likely that the second peak is accompanied by a chemical reaction taking place at the polymer electrode, it is possible to obtain a lightly AsF₆^?-doped sample for applied potentials lower than 0.6 V (versus Ag/Ag⁺). Very similar results are obtained with BF₄^? and ClO₄^? doping anions.     

Ionic liquid doped poly(N-methyl 4-vinylpyridine iodide) solid polymer electrolyte for dye-sensitized solar cell

Ion conducting polymer electrolyte, poly(N-methyl 4-vinylpyridine iodide) (PVPI) is synthesized for dye-sensitized solar cell (DSSC) application. A new solid polymer electrolyte composite containing low viscosity ionic liquid (IL) 1-ethyl 3-methylimidazolium dicyanamide (EMImDCN) doped PVPI is developed and its structural, electrical and photoelectrochemical studies are presented in detail. Fourier transform infrared (FTIR) spectroscopy, proton NMR and atomic force microscopy (AFM) affirms the modified polymer and its composite nature with porous surface morphology. The developed solid polymer electrolyte shows enhancement in ionic conductivity (σ) due to IL doping. The maximum σ value of 9.12 × 10^?6 S cm^?1 was obtained at 40 wt% IL concentration. The redox behavior of the electrolyte has been verified by the cyclic voltammetry studies. For device application, we have fabricated a DSSC using this solid polymer–IL electrolyte system which shows energy conversion efficiency of the solid-state cell as 0.65% under irradiation of simulated sunlight (AM 1.5, 100 mW cm^?2).     

Nickel-lithium oxide alloy transparent conducting films deposited by spray pyrolysis technique

In this research, nickel oxide (NiO) transparent semiconducting films are prepared by spray pyrolysis technique on glass substrates. The effect of Ni concentration in initial solution and substrate temperature on the structural, electrical, thermoelectrical, optical and photoconductivity properties of NiO thin films are studied. The results of investigations show that optimum Ni concentration and suitable substrate temperature for preparation of basic undoped NiO thin films with p-type conductivity and high optical transparency is 0.1 M and 450 °C, respectively. Then, by using these optimized deposition parameters, nickel-lithium oxide ((Li:Ni)O_x) alloy films are prepared. The XRD structural analysis indicate the formation of the cubic structure of NiO and (Li:Ni)O_x alloy films. Also, in high Li doping levels, Ni₂O₃ and NiCl₂ phases are observed. The electrical measurements show that the resistance of the films decreases with increasing Li level up to 50 at%. For these films, the optical band gap and carrier concentration are obtained to be 3.6 eV and 10¹⁵-10¹⁸ cm⁻³, respectively.     

Effect of various parameters on the conductivity of free standing electrosynthesized polypyrrole films

Electrical characteristics of polypyrrole films electrodeposited in different aqueous electrolyte solutions including p-toluenesulfonate, naphtalenesulfonate, nitrate, tetrafluoroborate, and perchlorate anions were investigated using the Van der Pauw procedure. The polymer films were synthesized by electrochemical oxidation at a fixed potential. Experimental parameters including the pyrrole concentration, electrolyte, applied potential and substrate were shown to affect the electrical conductivity σ of polypyrrole films. Since the substrate contributes significantly to the overall conductivity of polypyrrole-coated electrodes, the results obtained with free standing polymer films appeared more reliable. The results indicated that the p-toluenesulfonate doped PPy film showed the highest average conductivity (σ_293 K = 4.5 × 10⁵ S m^?1) whereas the perchlorate doped one produced the lowest of all the films prepared (σ_293 K = 2 × 10⁴ S m^?1).     

Thermal, micro-structural, and electrical properties of a La1−x Sr x Mn0.85Fe0.05Co0.05Ni0.05O3+δ (x = 0–0.4 mole) cathode system

The oxygen stoichiometry, thermal expansion, morphology, and electrical conductivity of a co-doped perovskitetype cathode system, La_1?x Sr _x Mn_0.85Fe_0.05Co_0.05Ni_0.05O_3+ä (x = 0–0.4 mole), are studied for intermediate-temperature solid oxide fuel cell applications. Sr²⁺-doping led to a decrease in the unit cell volume, oxygen stoichiometry, particle size, and activation energy, and an increase in the coefficient of thermal expansion and electrical conductivity. The sample with x = 0.3 mole exhibited four to five fold weight loss with respect to La_0.75Sr_0.25MnO_3+δ at an intermediate temperature range and suggested the availability of a large number of oxygen vacancies due to a co-doping effect. This sample also showed sufficiently high electrical conductivity (～76 S cm^?1) at 650 °C, a low activation energy (～0.15 eV), and a coefficient of thermal expansion (～12.1 × 10^?6 °C^?1) comparable to those of the adjacent components and submicron sized particles. The experimental results are explained using defect models.     

Synthesis and properties of chemically coupled poly(thiophene)

We describe the synthesis and physical properties of poly(thiophene) with a molecular weight of approximately 4000 consisting of 46 – 47 thiophene rings (184 – 188 carbons along the backbone). The pristine polymer exhibits an ESR line similar to that of cis-(CH)_x; the small number of unpaired spins is consistent with relatively high-quality material. The electrical conductivity can be increased by nearly ten orders of magnitude to values in excess of $\text{10 Ω}{}^{\mathrm{?1}}\text{cm}{}^{\mathrm{?1}}$ upon partial oxidation by AsF₅. The magnitude and temperature dependence of the thermopower of the doped polymer (24 mol%) are consistent with metallic behavior. The decrease in conductivity as the temperature is lowered and the magnitude of π at room temperature apparently result from the macroscopic transport being limited by interparticle contacts.     

New conductive polymeric materials: Cofacial assembly of mixed valent metallomacrocycles

This paper reports on an approach to control molecular stacking interactions in low-dimensional mixed valence materials by locking partially oxidized metallomacrocycles together in a cofacial orientation. Iodine doping of the face-to-face linked oligomers [M(Pc)O]_n (M = Si, Ge, Sn; Pc = phthalocyaninato) produces electrically conductive polymers {[M(Pc)O]I_xn with a wide range of x stoichiometries. Resonance Raman spectroscopy indicates that the iodine has oxidized the polymer chain. Polymer structure has been studied by X-ray powder diffraction, and it is possible to estimate interplanar spacings. Halogen doping of the [M(Pc)O]_n materials is accompanied by electrical conductivity increases as large 10⁷ (ohm cm)^?1; the general trend is $\text{σ}{}_{\mathrm{<mtext>Si</mtext>}}\text{? σ}{}_{\mathrm{<mtext>Ge</mtext>}}\text{> σ}{}_{\mathrm{<mtext>Sn</mtext>}}$. Variable temperature conductivity and magnetic susceptibility data are reported.