Raman scattering and electrical conductivity of nitrogen implanted MoO3 whiskers

Whiskers of MoO₃ have been grown by a thermal transport process. A set of samples was then implanted with nitrogen ions at a dose of 5 × 10¹⁶ ion/cm². The implanted whiskers changed from transparent to semi-transparent. Raman spectroscopy of the whiskers was observed and compared with those of unimplanted whiskers. The results revealed that the Raman intensity of the implanted whiskers was decreased about 10 times with respect to that of unimplanted whiskers. Only the case of the wave propagation parallel to the a-axis, a lower suppression ratio of the B_3g modes was observed. No extra mode due to the nitrogen implantation was observed. This indicates that implantation could only induce defects and oxygen vacancies but not the structural transformation. From electrical conductivity and Hall measurement, it was found that the whiskers exhibited an n-type semiconductor and its conductivity drastically increased due to the defects and oxygen vacancies.     

Preparation and electrical conductivity of polyethers/WS2 layered nanocomposites

Utilizing the solvothermal synthesis technique, lithium intercalated tungsten disulfide Li_xWS₂ with x > 1 was obtained, which was allowed to react with water to the formation of single-molecule-layer suspension of tungsten disulfide. The layered nanocomposites PEG, PEO/WS₂, intercalating poly(ethylene glycol) (PEG, MW ≈ 1 × 10³, 6 × 10³, 1 × 10⁴) and poly(ethylene oxide) (PEO, MW ≈ 3 × 10⁵) into the tungsten disulfide host galleries, were prepared using the improved exfoliation-adsorption technique. It was revealed that the intercalated polymers within the host galleries are in a double-layer arrangement with an interlayer expansion of about 9 Å. Despite high conductivity of the host material, those of the PEG, PEO/WS₂ nanocomposites were found to be high in the order of 1 × 10⁻² to 10⁻³ S cm⁻¹ at ambient temperature, resulted from the guest-host charge transfers.     

Effect of double doping on crystal structure and electrical conductivity of CaO and WO3-doped Bi2O3

The atomic arrangement of WO₃-doped Bi₂O₃ was found similar to that of the fluorite structure. However, the electrical conductivity of WO₃-doped Bi₂O₃ is significantly lower than that of commonly used Y₂O₃-doped Bi₂O₃. The structure and electrical conductivity of samples formulated as (Ca_xW_0.15Bi_0.85−x)₂O_3.45−x (x = 0, 0.1, 0.2 and 0.3) were investigated. The as-sintered (W_0.15Bi_0.85)₂O_3.45 and (Ca_0.1W_0.15Bi_0.75)₂O_3.35 exhibit similar single tetragonal structure that is isostructural with 7Bi₂O₃·2WO₃. Therefore, (W_0.15Bi_0.85)₂O_3.45 and (Ca_0.1W_0.15Bi_0.75)₂O_3.35 formed a superstructure consisting of 10 enlarged cubic fluorite subcells. However, the as-sintered samples consist of a tetragonal structure and tetragonal CaWO₄ for x = 0.2 and 0.3 because the oxygen vacancy concentration increases. The conductivities of (Ca_xW_0.15Bi_0.85−x)₂O_3.45−x (x = 0, 0.1, 0.2 and 0.3) did not exhibit linear dependence with x value. The best conductivity is 2.35 × 10⁻² S cm⁻¹ at 700 °C for x = 0.1 that is higher than that of Ca-free (W_0.15Bi_0.85)₂O_3.45. The higher conductivity of (Ca_0.1W_0.15Bi_0.75)₂O_3.35 than (W_0.15Bi_0.85)₂O_3.45 may result from the higher anion vacancy concentration and more symmetrical structure.     

Low-temperature hydrogen transfer and cracking catalysis in molten SbCl3-AlCl3

Molten SbCl₃-10 mol% AlCl₃ has been found to catalyse unusual hydrogen transfer chemistry for the polycyclic aromatic hydrocarbon, naphthalene, under extremely mild, aprotic conditions. At 130 °C and in the absence of added hydrogen gas, naphthalene is rapidly hydrogenated and isomerized in the melt to form 1-methylindene, 1-methylindane, and tetralin. The hydrogen used in the formation of these products is generated internally from the coupling of a portion of the naphthalene to form condensed aromatics such as binaphthalenes, benzofluoranthenes, and perylene. Furthermore, many of these condensed products not only undergo similar hydrogenation and isomerization, but they are also severely cracked in this medium. Under these aprotic, low-temperature reaction conditions, the redox properties of SbCl₃ are believed to play a key role in the catalytic process, the effect of added AlCl₃ being to enhance the oxidizing power of the SbCl₃ in addition to increasing the Lewis acidity of the melt.     

Synthesis,characterization and electrical conductivity of BaTh1-xYbxO3-x/2

Pristine as well as ytterbium substituted barium thorates, BaTh_1-xYb_xO_3-δ (x?=?0–0.2) were synthesized using a modified solid state method. Electrical conductivity behavior of the sintered specimens in various atmospheres in temperature range from 300 to 600 °C was explained. Substitution of ytterbium into barium thorate was found to enhance its conductivity in oxygen ambience. The same was found to be enhanced further when the ambience was changed to hydrogen for the composition up to x?=?0.1 but, marginally decreased from thereon for the composition with x?=?0.15. Retention of hydrogen in thorate matrix was elucidated.     

Viscosity of NaFAlF3Al2O3 melt mixtures

Melt viscosities for the system NaFAlF₃Al₂O₃ over the experimentally accessible range are reported, the limiting factors being the solubility of Al₂O₃ and the vapour pressure. The temperature extends from the liquidus temperature to 1100°C. A recently developed precision oscillation viscometer is utilized. The results are discussed in a qualitative fashion.     

Influence of Mn doping on electrical conductivity of lead free BaZrTiO3 perovskite ceramic

Mn doped barium zirconate titanate lead free ceramic with formula BaZr_.045(Mn_xTi_1-x) _.955 O₃ for x?=?0.00, 0.01, 0.02 and 0.03 has been prepared by solid-state reaction method. The single phase tetragonal structure was confirmed by X-ray diffraction (XRD) pattern using Rietveld refinement. Scanning electron microscopy (SEM) shows an inhomogeneous distribution of randomly oriented grains with some voids. Electrical conductivity of Mn doped BZT ceramics was studied using impedance analyzer in the temperature range 493K–673K over wide frequency window. The dispersion behaviour in electrical conductivity obeys Jonscher's double power law for Mn free compound, while it follows single power law for Mn doped compositions. Various parameters viz. dc conductivity (σ_dc), pre-exponential factor (A), frequency exponent (s) and activation energy (E_a) have been estimated by the theoretical fitting of experimental data. The reciprocal temperature dependence of dc conductivity follows the Arrhenius law and specifies thermally activated conduction mechanism. The obtained value of activation energy (E_a) evidences the conduction mechanism is induced by the migration of oxygen vacancies and oxide ions. All samples shows Negative temperature coefficient of resistance (NTCR) and hence exhibit semiconducting behaviour. The environmental friendly lead free ceramic can be exploit to design advanced materials and suitable for the fuel cell electrolyte/electrode applications.     

Current/voltage relationship in molten LiF-GdF3-Gd2 O3 Electrolyte with graphite anode

Polarization curves have been obtained in molten LiF-GdF₃, with and without added Gd₂O₃, both by a steady state (stepwise voltage increase) and voltage sweep methods. The results obtained by the former method are more reproducible.In the voltage range 2–9 V the curves pass through 3 distinct current peaks, of which the first one corresponds to discharge of oxide ions, as it is virtually absent in a purified melt. The second peak probably involves discharge of fluoride ions together with oxide ions. The interpretation of the third and largest peak is uncertain. Its relative size is a feature peculiar to this system. In similar systems, studied by other authors, the anode effect occurs at the corresponding voltage. The possibility of a catalyzed formation of CF₄ in this voltage area is postulated.     

Thermal conductivity of AlN ceramics sintered with CaF2 and YF3

Dense AlN ceramics with a thermal conductivity of 180W/m·K were obtained at the sintering temperature of 1750 °C using CaF₂ and YF₃ as additives. At temperatures below 1650 °C, the shrinkage of AlN ceramics is promoted by liquid (Ca,Y)F₂ and Ca₁₂Al₁₄O₃₂F₂. Liquid CaYAlO₄ mainly improves the densification of the sample when the sintering temperature increases to 1750 °C. The formation of liquid (Ca,Y)F₂ at a relatively low temperature results in homogeneous YF₃ distribution around the AlN particles, which benefits the removal of oxygen impurity in the AlN lattice, and thus a higher thermal conductivity.     

Ionic conduction in anodic oxide films on aluminium in molten LiNO3 + KNO3 + NaNO3 electrolyte

Steady-state ionic conduction studies in the anodic growth of films on aluminium in molten LiNO₃ + NaNO₃ + KNO₃ have been made. The breakdown voltage of the film is 73 V, unaffected by change of cd or temperature. The film-forming characteristics of anodic oxide films on aluminium in molten salt electrolytes are different from that of anodic films formed in aqueous electrolytes. The Tafel slope decreases with increase of temperature. Dignam's equation for ionic conduction has been examined critically. His parameter μ^* depends on temperature, whereas i₀ and φ are temperature-independent, which explains the variation of Tafel slope with temperature.     

Synthesis of CoAl2O4 by double decomposition reaction between LiAlO2 and molten KCoCl3

Submicronic CoAl₂O₄ powders were prepared by double decomposition reaction between solid LiAlO₂ and molten KCoCl₃ at 500 °C for 24 h. The reaction mechanism involves the dissolution of LiAlO₂ shifted by the precipitation of CoAl₂O₄ until complete transformation and the reaction leads to powders with a very homogeneous chemical composition. The powders obtained were mainly characterized by XRD, FTIR, ICP, X.EDS, electron microscopy and diffraction and diffuse reflexion. The blue pigments obtained exhibit a high thermic stability allowing their use for the colouring of ceramic tiles.     

Internal cation mobility in molten LiCl-NdCl3 system

Internal mobilities of Li⁺ and Nd³⁺ cations have been investigated in binary unsymmetrical molten LiCl-NdCl₃ system by countercurrent electromigration method (so-called Klemm method). The results have been presented as isotherms of cation internal mobilities versus equivalent fraction of NdCl₃ for 1023, 1073 and 1123 K and have been compared with corresponding relationships for NaCl-NdCl₃ and KCl-NdCl₃ systems. It has been found that internal mobility of Nd³⁺ ions (as well as Li⁺) increases with decreasing concentration of NdCl₃, contrary to KCl-NdCl₃ and NaCl-NdCl₃ systems for which Nd³⁺ internal mobility decreases or is nearly constant, respectively. The tendency that smaller alkali metal cation enhances internal mobility of trivalent ion (b_Ln) has been described with a simple equation: , where is the internal mobility of Ln³⁺ in molten LnCl₃, yLnCl₃ the equivalent fraction of LnCl₃ and a parameter is the difference between internal mobility of Ln³⁺ cation in molten LnCl₃ and internal mobility of this cation in infinitely diluted solution of LnCl₃ in alkali metal chloride.     

Fabrication and electrical properties of Pb(Co1/3Nb2/3)O3 ceramics

Pb(Co_1/3Nb_2/3)O₃ (PCN) ceramics have been produced by sintering PCN powders synthesized from lead oxide (PbO) and cobalt niobate (CoNb₂O₆) with an effective method developed for minimizing the level of PbO loss during sintering. Attention has been focused on relationships between sintering conditions, phase formation, density, microstructural development, dielectric and ferroelectric properties of the sintered ceramics. From X-ray diffraction analysis, the optimum sintering temperature for the high purity PCN phase was found at approximately 1050 and 1100 °C. The densities of sintered PCN ceramics increased with increasing sintering temperature. However, it is also observed that at very high temperature the density began to decrease. PCN ceramic sintered at 1050 °C has small grain size with variation in grain shape. There is insignificant change of dielectric properties with sintering temperature. The P–E hysteresis loops observed at −70 °C are of slim-loop type with small remanent polarization values, which confirmed relaxor ferroelectric behavior of PCN ceramics.     

The effect of co-doping with MgO and Yb2O3 on the structure and electrical conductivity of the Sm2Zr2O7 pyrochlore

SmYb_1−xMg_xZr₂O_7−x/2 (0 ≤ x ≤ 0.15) ceramics are pressureless-sintered at 1973 K for 10 h in air. The structure and electrical conductivity of SmYb_1−xMg_xZr₂O_7−x/2 ceramics are investigated by the X-ray diffraction, scanning electron microscopy and impedance spectroscopy measurements. SmYb_1−xMg_xZr₂O_7−x/2 ceramics exhibit a defect fluorite-type structure. The measured electrical conductivities of SmYb_1−xMg_xZr₂O_7−x/2 ceramics obey the Arrhenius relation, and electrical conductivity of each composition increases with increasing temperature from 673 to 1173 K. At identical temperature levels, the electrical conductivity of SmYb_1−xMg_xZr₂O_7−x/2 ceramics gradually increases with increasing magnesia content. SmYb_1−xMg_xZr₂O_7−x/2 ceramics are oxide-ion conductors in the oxygen partial pressure range of 1.0 × 10⁻⁴ to 1.0 atm at all test temperature levels. The electrical conductivity obtained in SmYb_1−xMg_xZr₂O_7−x/2 ceramics reaches the highest value of 2.72 × 10⁻³ S cm⁻¹ at 1173 K for the SmYb_0.85Mg_0.15Zr₂O_6.925 ceramic.     

Reduction of NOx in C3H6/air mixtures over Cu/Al2O3 catalysts

The reduction of nitrogen oxides by propene in the presence of air under net oxidising conditions has been studied for two Cu/alumina catalysts of low (1%) and high (5%) copper loadings in a flow microreactor and by DRIFT. The reaction was studied in the range 473–773 K using mixtures of 2.5% NO, 1% C₃H₆ and 10% O₂ with a balance of nitrogen or helium, using samples which were pretreated in air at 673 K and also over samples which had been pre-exposed to SO₂ at 473 K. The surface species present under reaction conditions have been identified and the sensitivity of their adsorption sites in the two different loaded catalysts to SO₂ pre-treatment has been investigated. SO₂ adsorption enhanced NO adsorption at 473 K in the absence of oxygen and, in reaction, enhanced formation of NCO species leading to increased levels of adsorbed CO as a decomposition product.     

Ionic conductivity of PEO9: Cu(CF3SO3)2: Al2O3 nano-composite solid polymer electrolyte

Cu⁺⁺ ion containing solid polymer electrolytes exhibit interesting electrochemical properties. In particular, the polymer electrolyte PEO₉:Cu(CF₃SO₃)₂ made by complexing copper triflate (CuTf₂) with PEO appears to show scientifically intriguing transport properties. Although some copper ion transport in these systems has been seen from plating stripping processes, the detailed mechanism of ionic transport and the species involved are yet to be established. In order to obtain enhanced ionic conductivities and also to contribute towards understanding the ionic transport process in Cu⁺⁺ ion containing, PEO based composite polymer electrolytes, we have studied the system PEO₉: CuTf₂: Al₂O₃ incorporating 10 wt.% of alumina filler particles of grain size 10 μm, 37 nm, 10–20 nm and also particles of pore size 5.8 nm. Thermal and electrical measurements show that the system remains amorphous down to room temperature. The composite electrolyte is predominantly an ionic conductor with electronic conductivity less than 2%. The triflate (CF₃SO₃⁻) anions appear to be the dominant carriers. The presence of alumina grains has enhanced the conductivity significantly from room temperature up to 100 °C. The nano-porous grains with 5.8 nm pore size and 150 m²/g specific surface area exhibited the maximum conductivity enhancement. This enhancement has been attributed to Lewis acid–base type surface interactions of ionic species with O²⁻ and OH⁻ groups on the filler grain surface.     

Effect of Ti substitution for Nb in double perovskite-type Ba3CaNb2O9 on chemical stability and electrical conductivity

This paper reports the synthesis, structure, chemical stability and electrical transport properties of Ti substituted Ba₃CaNb₂O₉ (BCN) to develop electrolytes for proton conducting solid oxide fuel cells (H-SOFCs). The powder X-ray diffraction (PXRD) of Ba₃CaNb_2−xTi_xO_9−δ (x = 0.1, 0.15, 0.2, 0.25 and 0.3) and Ba₃Ca_1.18Nb_1.82−xTi_xO_9−δ (x = 0.15 and 0.25) showed formation of double perovskite-like structure with lattice constant comparable to that of Ba₃Ca_1.18Nb_1.82O_9−δ (BCN18). Scanning electron microscopy (SEM) showed dense and pore-free microstructure for Ba₃CaNb_1.75Ti_0.25O_8.875. PXRD and Fourier transform infrared (FTIR) spectroscopy data confirmed long-term stability of Ba₃CaNb_2−xTi_xO_9−δ and Ba₃Ca_1.18Nb_1.82−xTi_xO_9−δ in boiling H₂O and in CO₂ at elevated temperatures. The AC impedance investigation showed contribution due to bulk, grain-boundary and electrode effect at low temperatures. The electrical conductivity of studied materials were measured in different medium including dry air, dry H₂, wet H₂, wet N₂ and D₂O. Increase in conductivity in wet N₂ and decrease in conductivity in D₂O confirmed the proton conduction in Ba₃CaNb_1.75Ti_0.25O_9-δ. Among Ti-substituted compounds investigated in this study, Ba₃Ca_1.18Nb_1.57Ti_0.25O_8.605 showed the highest conductivity of 3.5 × 10⁻⁴ S cm⁻¹ at 400 °C in wet N₂ (3%H₂O), which is comparable to reported values of Ba₂Ca_0.79Nb_0.66Ta_0.55O_6−δ and BCN18.     

Electrical conductivity relaxation in PVOH-LiClO4-Al2O3

We report on electrical conductivity relaxation measurements of solid polymer electrolytes (SPE) based on poly(vinyl alcohol) (PVOH) and LiClO₄ in which nanoporous Al₂O₃ particles with average pore diameter of 58 Å were dispersed. A power law frequency dependence of the real part of the electrical conductivity is observed as a function of temperature and composition. This behaviour is typical of systems in which correlated ionic motions in the SPE bulk material are responsible for ionic conductivity. This variation is well fitted to a Jonscher expression σ′(ω) = σ₀[1 + (ω/ω₀)^p] where σ₀ is the dc conductivity, ω₀ the characteristic angular frequency relaxation and p is the fractional exponent between 0 and 1. For a prototype membrane with composition 0.9PVOH − 0.1LiClO₄ + 7 wt.%Al₂O₃, it was found that the temperature dependence of σ₀ and ω₀, may be described by the VTF relationship, ? = ?₀ exp[−B/(T − T₀)], with approximately the same constant B and reference temperature T₀, indicating that ion mobility is coupled to the motions of the polymer chains. Moreover, p decreased with increasing temperature, from 0.68 at T = 319 K, to 0.4 at T = 437 K, indicating weaker correlation effects among mobile ions when the temperature is increased.     

In situ study of ionic conductivity for polyether-LiCF3SO3 electrolytes with subcritical and supercritical CO2

In situ measurements of the ionic conductivity were performed on polyethers, poly(ethylene oxide) (PEO) and poly(oligo oxyethylene methacrylate) (PMEO), with lithium triflate (LiCF₃SO₃) as crystalline and amorphous electrolytes, and at CO₂ pressures up to 20 MPa. Both PEO and PMEO systems in subcritical and supercritical CO₂ increased more than five fold in ionic conductivity at 40 °C composed to atmospheric pressure. The pressure dependence of the ionic conductivity for PEO electrolytes was positive under CO₂, and increased by two orders of magnitude under pressurization from 0 to 20 MPa, whereas it decreases with increasing pressure of N₂. The enhancement is caused by the plasticizing effect of CO₂ molecules that penetrate into the electrolytes.