High-temperature electrical transport in Al-doped calcium and strontium titanates

The electrical conductivity of perovskite-related oxides CaTi_1−xAl_xO_3−δ and SrTi_1−xAl_xO_3−δ (x=0−0.4) were investigated within the temperature range 900 to 1000 °C and the oxygen partial pressure range between 10⁻²⁰ and 0.21 atm using a dc four-point technique. The materials investigated show predominantly p-type electronic conductivity at high, n-type electronic conductivity at low, and ionic conductivity at intermediate oxygen partial pressures. The values of ionic conductivity in CaTi_1−xAl_xO_3−δ were found to be lower than those in CaTi_1−xFe_xO_3−δ. The effect of aluminium concentration on the high-temperature transport properties was examined. Paper presented at the 9th EuroConference on Ionics, Ixia, Rhodes, Greece, Sept. 15 – 21, 2002.     

AC Conductivity,XRD and transport properties of melt quenched PbI<Subscript>2</Subscript>–Ag<Subscript>2</Subscript>O–Cr<Subscript>2</Subscript>O<Subscript>3</Subscript> system

Composite materials used for electrode and electrolyte materials have been intensely studied in view of their advantages such as higher conductivity and better operational performance compared to their single-phase counterparts. The present work aims at studying the electrical and structural characteristics of a new composite electrolyte namely, (PbI₂) _x  − (Ag₂O–Cr₂O₃)_100−x where x = 5, 10, 15, 20, and 25 mol%, respectively, prepared by the melt quenching technique. The room temperature X-ray diffraction spectra revealed certain crystalline phases in the samples. AC conductivity analysis for all the prepared samples was carried out over the frequency range 1 MHz–20 Hz and in the temperature window 297–468 K. The room temperature conductivity values were calculated to be in the order of 10⁻⁵–10⁻³ Scm⁻¹. An Arrhenius dependence of temperature with conductivity was observed, and the activation energies calculated were found to be in the range 0.27–0.31 eV. Furthermore, the total ionic transport number (t _i) values obtained for all these indicated the ionic nature of this system. Paper presented at the Third International Conference on Ionic Devices (ICID 2006), Chennai, Tamilnadu, India, Dec. 7–9, 2006.     

Measurement of ionic conductivity of poly (<Emphasis Type="Italic">N</Emphasis>-vinylimidazole) and its fluoroborate salt in solid state

The conductivity of poly(N-vinylimidazole) (PVIM) and its fluoroborate salt (PVIM–HBF₄) are reported here. N-vinylimidazole is polymerized by free radical method and PVIM–HBF₄ is prepared by acidification of PVIM with HBF₄. The polyelectrolyte so formed has been characterized by infrared, hydrogen-1 nuclear magnetic resonance, thermogravimetric analyzer, and differential scanning calorimetry. Frequency and temperature dependence of AC conductivity has been studied to learn about the electrical conduction behavior in the materials. The electrical conductivity of the new material is found to be in the range of 10⁻⁵ to 10⁻⁶ S cm⁻¹.There is about 10²- to 10³-fold increase in conductivity of the polyelectrolyte. The material is shown to be a predominantly ionic conductor with t _ion ≈ 0.88. Apparent activation energies are found to be 0.397 and 0.250 eV for the polymer and the polyelectrolyte, respectively.     

Influence of acceptor doping on ionic conductivity in alkali earth titanate perovskites

The electrical conductivity of the SrTi_1−xFe_xO_3−δ, BaTi_1−xFe_xO_3−δ and SrTi_1−xMn_xO_3−δ systems has been studied in a range of oxygen partial pressures between 10⁻¹⁶ and 0.21 atm at 900 and 1000 °C. The materials exhibit predominantly ionic conductivity in a wide range of intermediate oxygen partial pressures. It has been found that in Fe doped strontium and barium titanates, the dependencies of the ionic conductivity on the acceptor concentration show a local maximum near x=0.2. Taking into account that in the CaTi_1−xFe_xO_3−δ system (x=0−0.5), the concentration dependence of the ionic conductivity also has a maximum near x=0.2, it can be concluded that this is a common phenomenon for Fe doped alkali earth titanates. An assumption has been made that a scheme of defect formation devised earlier for Fe doped calcium titanate is applicable for other alkali earth titanates.     

Electrical characterization of highly Titania doped YSZ

The defect fluorite region of the ternary system ZrO₂-Y₂O₃-TiO₂ encompasses compositions which offer both, good electronic and oxygen ion conductivity which enable good catalytic activity for the direct oxidation of methane in a solid oxide fuel cell (SOFC). The electrical properties of compositions Y_xTi_yZr_1−(x+y)O_2−x/2 (with x=0.15, 0.2, 0.25 and y=0.15, 0.18) were characterised in order to find the composition with highest ionic and electronic conductivity. High titanium dopant concentrations (Y) of 15 and 18 atom%, near the solubility limit of Ti⁴⁺ in the fluorite structure, have been introduced to achieve a high electronic conductivity at low oxygen partial pressure. The yttrium content x has been varied between 15 and 25 atom% to find the fluorite composition with the highest ionic conductivity for each titanium level. In the pO₂-range from 0.21 to 10⁻¹³ atm the conductivity is predominantly ionic and constant over that range. The maximum ionic conductivity is 0.01 Scm⁻¹ for the compositions, which contain 15 atom% yttrium. Substantial electronic conductivity is introduced into the system at low oxygen pressures below 10⁻¹³ atm via reduction of Ti⁴⁺ ions to Ti³⁺. The maximum electronic conductivity of 0.2 Scm⁻¹ at 930 °C has been measured for a sample with 18 atom% titanium. The slope of all log(σ) vs. log(pO₂) plots follows a pO ₂ ^−1/4 -dependence. Paper presented at the 5th Euroconference on Solid State Ionics, Benalmádena, Spain, Sept. 13–20, 1998.     

Magnetic-field-induced retardation of the recombination of nonequilibrium charge carriers in semiconductors

The retardation of the recombination of electrons and holes in semiconductors in an applied uniform magnetic field has been predicted. It has been shown that the recombination time in germanium in the temperature range of T = 1–10 K at charge carrier densities of n _e = 10¹⁰−10¹⁴ cm⁻³ in magnetic fields of B = 3 × 10²−3 × 10⁴ G can be more than two orders of magnitude larger than that at zero magnetic field. This means that, after creation of nonequilibrium charge carriers by their injection at the p-n junction owing to some radiation sources or fast electron irradiation, the semiconductor retains its conductivity for a much longer time at nonzero applied magnetic field. The effect under study can be used, for example, to detect radiation sources.     

Crystal growth,electrical and photophysical properties of Tl<Subscript>2</Subscript>S layered single crystals

The Tl₂S compound was prepared in a single crystal form using a special local technique, and the obtained crystals were analysed by X-ray diffraction. For the resultant crystals, the electrical properties (electrical conductivity and Hall effect) and steady-state photoconductivity were elucidated in this work. The electrical measurements extend from 170 to 430 K, where it was found that σ _⊥ = 8.82 × 10⁻⁵ Sm⁻¹ when current flow direction makes right angle to the cleavage plane of the crystals. In the same range of temperatures, it was found that σ _‖ = 4.73 × 10⁻⁵ Sm⁻¹ when the current flow is parallel to the cleavage plane. In line with the investigated range of temperatures, the widths of the band gaps were calculated and discussed as also the results of the electrical conductivity and Hall effect measurements. In addition, the anisotropy of the electrical conductivity (σ _⊥/σ _‖) for the obtained crystals was also studied in this work. Finally the photosensitivity was calculated for different levels of illumination as a result of the photoconductivity measurements, which showed that the recombination process in Tl₂S single crystals is a monomolecular process.      

Ion transport in proton conducting solid polymer electrolytes

In this communication the ion transport properties of polyvinyl alcohol complexed with orthophosphoric acid (H₃PO₄) have been investigated. The proton conduction is confirmed by hydrogen gas evolved at the cathode of the coulometer and the transference number of H⁺ ion has been determined. The transient ionic current (TIC) technique has been used to detect the mobile ionic species and their mobilities are evaluated. The ionic mobility was found to be of the order of 10⁻⁴ cm².V⁻¹.s⁻¹ for H⁺ ions. It is observed that the bulk electrical conductivity increases with the temperature following the Arrhenius type behaviour. Variation of charge carrier concentration with the molar ratio of H₃PO₄ in the sample reveals that the carrier concentration is largely affected by the amount of dopant in the complexes.     

Effect of PVAc dispersal into PVA-NH4SCN polymer electrolyte

The present paper deals with ion transport studies on a new proton conducting composite polymer electrolyte — (PVA_x:NH₄SCN)_y:PVAc system. Complexation and morphology of the composite electrolyte films are discussed on the basis of X-ray diffraction and differential scanning calorimetry data. Coulometry and transient ionic current measurements revealed charge transport through protons. The maximum ion conductivity was found to be 7.4·10⁻⁴ S·cm⁻¹ for the composition: x=0.15, y=0.12. The observed conductivity behaviour is correlated to the morphology of the films. The temperature dependence of the electrical conductivity exhibits Arrhenius characteristics in two different temperature ranges separated by a plateau region related to morphological changes occurring in the electrolyte.     

Ionic conduction behavior in PVC–PEG blend polymer electrolytes upon the addition of TiO2

The blend-based polymer electrolyte consisting of poly (vinyl chloride) (PVC) and poly (ethylene glycol) (PEG) as host polymers and lithium perchlorate (LiClO₄) as the complexing salt was studied. An attempt was made to investigate the effect of TiO₂ concentration in the unplasticized PVC–PEG polymer electrolyte system. The XRD and FTIR studies confirm the formation of a polymer–salt complex. The conductivity results indicate that the incorporation of ceramic filler up to a certain concentration (15 wt.%) increases the ionic conductivity and upon further addition the conductivity decreases. The maximum ionic conductivity 0.012 × 10⁻⁴ S cm⁻¹ is obtained for PVC–PEG–LiClO₄–TiO₂ (75–25–5–15) system. Thermal stability of the polymer electrolyte is ascertained from TG/DTA studies.     

Structural and electrochemical characteristics of 49% PMMA grafted polyisoprene-LiCF3SO3-PC based polymer electrolytes

Gel polymer electrolytes consisting of 49% PMMA grafted polyisoprene-LiCF₃SO₃, were plasticized with propylene carbonate (PC) are reported. The effect of PC on the electrochemical properties of the polymer electrolyte has been investigated. Analysis of FTIR spectra shows the interaction of salt and plasticizers with the polymer chain. The ionic conductivity was measured and exhibited a maximum value of 10⁻⁴ S/cm. The temperature dependence of the electrical conductivity follows the Arrhenius law. Paper presented at the International Conference on Functional Materials and Devices 2005, Kuala Lumpur, Malaysia, June 6 – 8, 2005.     

Quantum oscillations of the resistivity and hall coefficient and the quantum limit in Bi<Subscript>0.93</Subscript>Sb<Subscript>0.07</Subscript> alloys in a magnetic field along the trigonal axis

The dependences of the electrical resistivity ρ and the Hall coefficient R on the magnetic field have been measured for single-crystal samples of the n-Bi_0.93Sb_0.07 semiconductor alloys with electron concentrations in the range 1 × 10¹⁶ cm⁻³ < n < 2 × 10¹⁸ cm⁻³. It has been found that the measured dependences exhibit Shubnikov-de Haas quantum oscillations. The magnetic fields corresponding to the maxima of the quantum oscillations of the electrical resistivity are in good agreement with the calculated values of the magnetic fields in which the Landau quantum level with the number N intersects the Fermi level. The quantum oscillations of the Hall coefficient with small numbers are characterized by a significant spin splitting. In a magnetic field directed along the trigonal axis, the quantum oscillations of the resistivity ρ and the Hall coefficient R are associated with electrons of the three-valley semiconductor and are in phase with the magnetic field. In the case of a magnetic field directed parallel to the binary axis, the quantum oscillations associated both with electrons of the secondary ellipsoids in weaker magnetic fields and with electrons of the main ellipsoid in strong magnetic fields (after the overflow of electrons from the secondary ellipsoids to the main ellipsoid) are also in phase. In magnetic fields of the quantum limit ħω _c /2 ≥ E _F, the electrical conductivity increases with an increase in the magnetic field: σ₂₂(H) ∼ H ^k . A theoretical evaluation of the exponent in this expression for a nonparabolic semiconductor leads to values of k close to the experimental values in the range 4 ≤ k ≤ 4.6, which were obtained for samples of the semiconductor alloys with different electron concentrations. A further increase in the magnetic field results in a decrease of the exponent k and in the transition to the inequality σ₂₂(H) ≤ σ₂₁(H).     

Electrical and magnetic properties of manganites La1 ? xAgxMnO3 (x = 0.05, 0.1, and 0.2) at 77 K < T < 300 K

The electrical conductivity, magnetization, and magnetoresistance of manganites La_{1 − x} Ag _x MnO₃ have been investigated in the temperature range 78–300 K. The samples have been synthesized by the sol-gel method. At room temperature, the magnetic field of 0.6 T has no effect on the electrical conductivity. As the temperature decreases, an abrupt jump is observed in the magnetization curve due to the semiconductor-metal phase transition. This transition hardly affects the temperature dependence of the resistance.     

Magnetic and structural transitions in La1−x Sr x MnO3: T-x phase diagram

The electrical conductivity, magnetic susceptibility, magnetization, and submillimeter (v=5∓20 cm⁻¹) permittivity and dynamic conductivity of La_1−x Sr _x MnO₃ (0≤x≤ 0.45) single crystals are investigated. The anomalies in the temperature dependences of these quantities are identified with diverse magnetic and structural phase transformations, including antiferromagnetic and ferromagnetic ordering, structural transitions between strongly distorted (Jahn-Teller) and weakly distorted (pseudocubic) orthorhombic phases, structural transitions to a rhombohedral phase and unusual transitions to a polaron-ordering state. As a result, the complete T-x phase diagram of the system La_1−2x Sr _x MnO₃ is constructed in a wide interval of temperatures T=4.2∓1050 K and concentrations x=0−0.45. Pis’ma Zh. éksp. Teor. Fiz. 68, No. 4, 331–336 (25 August 1998)     

Structural and ionic conductivity studies on P(ECH-EO):γ-BL:LiClO<Subscript>4</Subscript> plasticized polymer electrolyte

The plasticized polymer electrolyte consisting of poly(epichlorohydrin-ethyleneoxide) [P(ECH-EO)], lithium perchlorate (LiClO₄) and γ-butyrolactone (γ-BL) have been prepared by simple solution casting technique. The polymer–salt–plasticizer complex has been confirmed by XRD analysis. The ionic conductivity studies have been carried out using AC impedance technique. The effect of plasticizer (γ-BL) on ionic conductivity has been discussed with respect to different temperatures. The maximum value of ionic conductivity is found to be 1.3 × 10⁻⁴ Scm⁻¹ for 70P(ECH-EO):15γ-BL:15LiClO₄ at 303 K. The temperature dependence of the plasticized polymer electrolyte follows the Vogel–Tamman–Fulcher formalism. The activation energy is found to decrease with the increase in plasticizer.     

Ionic transport, thermal, XRD, and phase morphological studies on LiCF3SO3-based PVC–PVdF gel electrolytes

The plasticized polymer electrolyte composed of polyvinylchloride (PVC) and polyvinylidene fluoride (PVdF) as host polymer, the mixture of ethylene carbonate and propylene carbonate as plasticizer, and LiCF₃SO₃ as a salt was studied. The effect of the PVC-to-PVdF blend ratio with the fixed plasticizer and salt content on the ionic conduction was investigated. The electrolyte films reveal a phase-separated morphology due to immiscibility of the PVC with plasticizer. Among the three blend ratios studied, 3:7 PVC–PVdF blend ratio has shown enhanced ionic conductivity of 1.47 × 10⁻⁵ S cm⁻¹ at ambient temperature, i.e., the ionic conductivity decreased with increasing PVC-to-PVdF ratio and increased with increasing temperature. A temperature dependency on ionic conductivity obeys the Arrhenius behavior. The melting endotherms corresponding to vinylidene (VdF) crystalline phases are observed in thermal analysis. Thermal study reveals the different levels of uptake of plasticizer by VdF crystallites. The decrease in amorphousity with increase in PVC in X-ray diffraction studies and larger pore size appearance for higher content of PVC in scanning electron microscopy images support the ionic conductivity variations with increase in blend ratios.     

A novel PEO-based composite polymer electrolyte with NaAlOSiO molecular sieves powders

Ion-conducting thin film polymer electrolytes based on poly(ethylene oxide) (PEO) complexes with NaAlOSiO molecular sieves powders has been prepared by solution casting technique. X-ray diffraction, scanning electron microscopy, differential scanning calorimeter, and alternating current impedance techniques are employed to investigate the effect of NaAlOSiO molecular sieves on the crystallization mechanism of PEO in composite polymer electrolyte. The experimental results show that NaAlOSiO powders have great influence on the growth stage of PEO spherulites. PEO crystallization decrease and the amorphous region that the lithium-ion transport is expanded by adding appropriate NaAlOSiO, which leads to drastic enhancement in the ionic conductivity of the (PEO)₁₆LiClO₄ electrolyte. The ionic conductivity of (PEO)₁₆LiClO₄-12 wt.% NaAlOSiO achieves (2.370 ± 0.082) × 10⁻⁴ S · cm⁻¹ at room temperature (18 °C). Without NaAlOSiO, the ionic conductivity has only (8.382 ± 0.927) × 10⁻⁶ S · cm⁻¹, enhancing 2 orders of magnitude. Compared with inorganic oxide as filler, the addition of NaAlOSiO molecular sieves powders can disperse homogeneously in the electrolyte matrix without forming any crystal phase and the growth stage of PEO spherulites can be hindered more effectively.     

Electrochemical study of P(VDF-HFP)/PMMA blended polymer electrolyte with high-temperature stability for polymer lithium secondary batteries

In the present study, a kind of solid polymer electrolyte (SPE) based on poly(vinylidene difluoride-co-hexafluoropropylene)/poly(methyl methacrylate) blends was prepared by a casting method to solve the safety problem of lithium secondary batteries. Owing to being plasticized with a room temperature ionic liquid, N-butyl-N′-methyl-imidiazolium hexafluorophosphate, the obtained SPE shows a thermal decomposition temperature over 300°C and an ionic conductivity close to 10⁻³ S cm⁻¹. The SPE-3 sample, in which the weight of two polymers is equivalent, possesses an ionic conductivity of 0.45 × 10⁻³ S cm⁻¹ at 25°C and presents an electrochemical window of 4.43 V. The ionic conductivity of the SPE-3 is as high as 1.73 × 10⁻³ S cm⁻¹ at 75°C approaching to that of liquid electrolyte. The electrochemical performances of the Li/LiFePO₄ cells confirmed its feasibility in lithium secondary batteries.     

Effect of high electric field on the dc conduction of TeO2-V2O5-MoO3 amorphous bulk material

Effect of high electric field on the dc conductivity of TeO₂-V₂O₅-MoO₃ amorphous bulk samples with different molar ratio of each component was investigated with gap-type electrode arrangement. At low electric fields, the current-voltage (I–V) characteristics has a linear shape, while at high electric fields (>10³ V/cm), bulk samples show nonlinear behavior (nonohmic conduction) and current-voltage characteristics shows increasing deviation from Ohm’s law with increasing current density. High-field effect of Pool-Frenkel type was observed at electrical fields about 10³−10⁴ V/cm. In addition, positive deviation from Pool-Frenkel effect was observed when a field higher than about 10⁴ V/cm was applied.     

Application of ionic liquid doped solid polymer electrolyte

The electrical, structural, and photoelectrochemical properties of the polymer electrolyte PEO:NaI/I₂ doped with an ionic liquid 1-ethyl 3-methylimidazolium dicyanamide (EMImDCN) have been reported. Incorporation of the ionic liquid (IL) increases the membrane homogeneity, decreased surface roughness, and enhances the short current (J _sc). Additionally, the doping of IL provides more charge carriers which enhances overall ionic conductivity (σ). The optimized σ was found at 40 wt.% IL composition. The fabricated DSSC using this new solid electrolyte showed 1.43% efficiency at 100 mW cm⁻².