Electronic Conductivity Measurements Research Articles

Electronic thermal conductivity measurements in intrinsic graphene

The electronic thermal conductivity of graphene and 2D Dirac materials is of fundamental interest and can play an important role in the performance of nano-scale devices. We report the electronic thermal conductivity, $K_{e}$, in suspended graphene in the nearly intrinsic regime over a temperature range of 20 to 300 K. We present a method to extract $K_{e}$ using two-point DC electron transport at low bias voltages, where the electron and lattice temperatures are decoupled. We find $K_e$ ranging from 0.5 to 11 W/m.K over the studied temperature range. The data are consistent with a model in which heat is carried by quasiparticles with the same mean free-path and velocity as graphene's charge carriers.

ELECTRONIC CONDUCTIVITY MEASUREMENTS IN SOLID ELECTROLYTES USING AN ION BLOCKING MICROELECTRODE: NOISE REJECTION BASED ON A MEDIAN FILTER

In this paper, a method of electronic conductivity measurement is presented. It combines two well known methods of electrochemistry: cyclic voltammetry and chronoamperometry. This DC technique uses the Hebb–Wagner approach to block ionic conduction (when steady state conditions are reached) and allows electronic conduction of solid electrolytes to be determined. In order to get short diffusion times, a micro contact is used as an ion blocking electrode. However, as the electronic conduction in electrolytes is and should be very low, the current is also very low, typically some tens of nanoamps. Thus, the heating system inevitably generates noise problems that are solved using a median filter. As opposed to other related work, our system allows the determination of the conductivities without any preliminary smoothing or fitting of the curves (since the noise is strongly reduced). Some results with oxygen ion conductors are also given.

Synthesis, spectroscopic studies, molecular modeling and antimicrobial activity of binuclear Co(II) and Cu(II) complexes of 4,6-diacetylresorcinol

Reactions of 4,6-diacetylresorcinol with different cobalt(II) and copper(II) salts viz., OAc−, Cl−, NO3- and SO42-, yielded a new series of binuclear metal complexes. Reactions of the ligand with these metal ions in the presence of a secondary ligand (L′) [O,O-donor; acetylacetone, N,O-donor; 8-hydroxyquinoline or N,N-donor; 1,10-phenanthroline and N,N,N′,N′-tetramethylethylenediamine] in 1:2:2 (L:M:L′) molar ratio yielded mixed-ligand complexes with different molar ratios. The metal complexes were characterized by elemental and thermal analyses, IR, electronic, ESR and mass spectra as well as conductivity and magnetic susceptibility measurements. The analytical and spectroscopic data suggested that the H2L ligand behaves as a neutral, monobasic or dibasic tetradentate ligand, depending on the type of the anion and secondary ligand used, through the two phenolic and two carbonyl groups. Electronic spectra, magnetic and conductivity measurements showed that all complexes are octahedral with non-electrolytic nature. The profile of ESR spectra of copper(II) complexes suggested the octahedral geometry and the spin Hamiltonian parameters of the complexes were calculated and discussed. Molecular orbital calculations were performed for metal complexes using Hyperchem 7.52 program on the bases of PM3 level and the results correlated with the experimental data. The free ligand and some of its metal complexes showed antimicrobial activity towards some of Gram-positive and Gram-negative bacteria, yeast (Candida albicans) and fungus (Aspergillus fumigatus).

Effect of Temperature on Structure and Electronic Properties of Nanometric Spinel-Type Cobalt Oxides

Temperature is shown to have a huge influence on the electronic properties of nanometric spinel-type cobalt oxides precipitated at low temperature in alkaline media. The initial phase, with formula HxLiyCo3−δO4, contains hydrogen, lithium, cobalt vacancies, and a mixed valence Co4+/Co3+ within the structure, leading to an electronic conductivity higher than that of stoichiometric Co3O4. Its structural evolution under thermal treatment was studied by X-ray diffraction and chemical analysis, which reveal modifications in structure and compositions, involving water release, increase of the Co/O atomic ratio, and modification of the Co4+/Co3+ ratio. The RT to 300 °C range is particularly interesting as a single-phase domain and the materials obtained in this temperature range were investigated by chemical analysis, electronic conductivity and specific surface area measurements. Upon increasing temperature, the enhancement of the Co4+/Co3+ ratio, together with cationic redistribution in the spinel framework, r...

Ln3FeGaQ7: A new series of transition-metal rare-earth chalcogenides

A new series of transition-metal rare-earth chalcogenides, Ln3FeGaQ7 (Ln=Nd, Sm, Gd, Dy, Q=S; Ln=Nd, Gd, Dy, Q=Se), have been synthesized by solid state reactions. They are isostructural and crystallize in the space group P63. They adopt a three-dimensional framework composed of LnQ7 monocapped trigonal prisms with the interesting ∞1[FeS3]4− chains and isolated GaQ4 tetrahedra lying in two sets of channels in the framework. Magnetic susceptibility measurements on Ln3FeGaQ7 (Ln=Gd, Dy; Q=S, Se) indicate that they are paramagnetic and obey the Curie–Weiss law. Based on the diffuse reflectance spectra, Ln3FeGaQ7 (Ln=Gd, Dy; Q=S, Se) should have band gaps smaller than 0.5 eV. Electronic conductivity measurement on Dy3FeGaSe7 demonstrates semiconducting behavior with σ300=0.124 S/cm. The first-principles calculations were also performed to study the electronic structures of these compounds.

Antibacterial Application of Novel Mixed-Ligand Dithiocarbamate Complexes of Nickel (II)

Nine stable mixed ligand dithiocarbamate complexes of Nickel (II) ion were prepared. The complexes were characterized with electronic spectroscopy, infrared spectroscopy, conductance measurement, melting point and percentage metal analysis. Resulting analytical data gave credence to the assignment of a tentative square planar geometry to all the complexes. The complexes were proposed to have a general formulae of (Ni(Sal)(Rdtc)), where Sal = salicylaldehyde; R = dibenzylamine(Bz2NH), methylphenylamine(MePhNH),pyrrolidineamine(pyrrolNH),piperidineamine(piperNH),morpholineamine(Morp NH), anilineamine(AnilNH), para-chloroanilineamine(p-ClAnilNH), toludineamine(TolNH) and anisidineamine(AnisNH); and dtc = dithiocarbamate anion. The metal complexes were screened against six different bacteria strain using Agar diffusion method. The antibacterial studies reveal that the metal complexes exhibit broad spectrum antibacterial activity against Escherichia coli, Staphylococcus aureus, Klebsiella oxytoca and Pseudomonas aureginosa with inhibitory range of 10.5.—20.0mm.

Microstructure and opto-electrical properties of SnO<SUB align="right">2:In<SUB align="right">2O<SUB align="right">3 alloys thin films prepared by ultrasonic spray

In this work, we study the effect of indium weight ratio in solution: R = [In/Sn] on the properties of SnO2:In2O3 thin films prepared by ultrasonic spray method at fixed temperature of 300°C. The used precursors are tin chloride dehydrate and indium trichloride dissolved in methanol. To prepare hybrid SnO2:In2O3 thin films with different concentrations, the ratio R is varied in the range of 10–95 wt%. The resulting films were characterised by X-ray diffraction, scanning electron microscopy analysis, UV-visible spectrophotometer and conductivity measurement. The XRD results indicate segregation between SnO2 and In2O3 phases in all films. The optical transmittance is in the range of [75–85]%. The conductivity values of pure oxides are very low [~10–3 (Ω.cm)–1] and it is increased with R ratio until a maximum value of 1.2 × 102 (Ω.cm)–1 obtained at R = 95 wt%. Consequently, the higher figure of merit (Fm = σ.T.d) is obtained at this later ratio.

Preparation of powders and films of the lithium ion conducting solid electrolyte Li1.3Al0.3Ti1.7(PO4)3

This paper describes a process for the preparation of powders and films of the lithium ion conducting solid electrolyte Li1.3Al0.3Ti1.7(PO4)3 from peroxide solutions. The use of peroxide solutions ensures the preparation of Li1.3Al0.3Ti1.7(PO4)3 with a room-temperature electrical conductivity of (4–5) × 10−4 S/cm by calcining a precursor at 800°C. The synthesized Li1.3Al0.3Ti1.7(PO4)3 powders were characterized by X-ray diffraction, thermal analysis (DTA/TG), and ionic and electronic conductivity measurements. The growth of Li1.3Al0.3Ti1.7(PO4)3 solid electrolyte films is described.

Preparation, Study and Theortical Treatment of Co(II) Ni(II) Cu(II) and Zn(II) Schiff Base Coplexes with Sodium [N-(hydroxyl naphtholidine) Glycine imino

Anew Schiff base (NaHL) has been prepared from the reaction between the salt of amino acid glycine with 2-hydroxy naphthaldehyde. By tridentate Schiff base of (ONO), donors were characterized by using U.V and spectrophotometer techniques. Complexes of Co(II) Ni(II) Cu(II) and Zn(II) ion with the ligand have been prepared, these complexes were identified by infrared, electronic spectral data, elemental analysis, magnetic moments, and molar conductivity measurements. It is concluded from the elemental analysis that all the complexes have (1:2) [metal:ligand] molar ratios, octahedral, with the exception to Zn(II) complex which have (1:1)[metal:ligand] molar ratio.

Preparation, Study and Theortical Treatment of Co(II) Ni(II) Cu(II) and Zn(II) Schiff Base Coplexes with Sodium [N-(hydroxyl naphtholidine) Glycine imino

Anew Schiff base (NaHL) has been prepared from the reaction between the salt of amino acid glycine with 2-hydroxy naphthaldehyde. By tridentate Schiff base of (ONO), donors were characterized by using U.V and spectrophotometer techniques. Complexes of Co(II) Ni(II) Cu(II) and Zn(II) ion with the ligand have been prepared, these complexes were identified by infrared, electronic spectral data, elemental analysis, magnetic moments, and molar conductivity measurements. It is concluded from the elemental analysis that all the complexes have (1:2) [metal:ligand] molar ratios, octahedral, with the exception to Zn(II) complex which have (1:1)[metal:ligand] molar ratio.

A conducting nanocomposite via intercalative polymerisation of 2-methylaniline with aniline in montmorillonite cation-exchanged

Polymer/montmorillonite nanocomposites were prepared. Intercalation of 2-methylaniline with aniline monomers into montmorillonite modified by cation was followed by subsequent oxidative polymerization of the monomers in the interlayer spacing. The clay was prepared by cation exchange process between sodium cation in (M-Na) and copper cation (M-Cu). We prepared a series of polymer/clay nanocomposite materials that consisted of an emeraldine base of poly(2-MA), poly(2-MA-co-ANI) and PANI by layered copper montmorillonite. All organic monomers used were first intercalated into the interlayer regions of clay hosts followed by a one-step in situ oxidative polymerization. The unique properties of the as-synthesized nanocomposites materials are investigated by electronic conductivity measurements, X-ray diffraction, FTIR spectroscopy, UV-vis spectroscopy, thermogravimetric analysis and SEM, were also studied by cyclic voltammetry which indicates the electroactive effect of nanocomposite gradually increased with aniline in the polymer chain.

Electrical conductivity of new zinc phosphate glass/metal composites

Zinc phosphate–glass/metal composites have been successfully prepared. Glass with composition of 45mol% ZnO–55mol% P2O5 (ZP) has been filled with metallic powders (nickel and cobalt). The glass matrix thermal stability has been assessed by differential thermal analysis technique. The morphology has been examined by scanning electronic microscopy, showing almost homogenous composites. Comparison between the measured and calculated densities as a function of metallic content exhibits a good coherence and allows the estimation of porosity inside the composites. X-ray diffraction analysis has revealed that the ZP-matrix phase is amorphous when the temperature treatment is below the glass transition temperature Tg. However, the principal peaks observed in the case of the composites have been assigned to the metallic crystals of nickel or cobalt fillers. It has been found that the phosphate glass phase is not affected by the growing of the metallic network. The electronic conductivity measurements versus filler volume fraction have been investigated for the first time on phosphate–glass/metal composites. This study has shown the occurrence of a conducting transition at around 30% filler volume fraction. The obtained result has been interpreted on the basis of the statistical percolation theory frame.

Platinum nanoparticles functionalized with acetylene derivatives: Electronic conductivity and electrocatalytic activity in oxygen reduction

Stable platinum nanoparticles were prepared by the self assembly of acetylene derivatives (1-alkynes, 4-ethylphenylacetylene, and 4-tert-butylphenylacetylene) onto bare Pt colloid surfaces. Transmission electron microscopic measurements showed that the nanoparticles exhibited an average core size of 2.85±0.62nm. FTIR study showed that with the acetylene ligands adsorbed onto the Pt nanoparticle surface, the CH vibrational stretches disappeared completely, along with a substantial redshift of the CC vibrational stretch, as compared to those of the monomeric ligands. These were ascribed to the breaking of the CH bond and the formation of PtsurfaceH and PtsurfaceC at the metal–ligand interface. The conjugated bonding interactions between the triple bond and Pt were found to lead to extensive intraparticle charge delocalization between the acetylene moieties, and hence unique photoluminescence properties of the nanoparticles. For nanoparticles functionalized with 4-ethylphenylacetylene or 4-tert-butylphenylacetylene, the excitation and emission peak positions showed an apparent redshift as compared to those of 1-alkyne-capped platinum nanoparticles. Electronic conductivity measurements of the nanoparticle solids showed that for the nanoparticles capped with 1-alkynes or 4-ethylphenylacetylene, the temperature dependence of the ensemble conductivity was consistent with that of semiconducting materials, whereas for the 4-tert-butylphenylacetylene-capped nanoparticles, metallic behaviors were observed instead. An apparent discrepancy was also observed in the electrocatalytic reduction of oxygen in alkaline media, where the specific activity was all markedly better than that of commercial Pt/C catalysts, with the best performance by the 4-ethyphenylacetylene-capped Pt nanoparticles. These observations were accounted for by the deliberate manipulation of the electronic structure of the Pt nanoparticles by the organic ligands.

The effects of pristine and carboxylated multi-walled carbon nanotubes as conductive additives on the performance of LiNi0.33Co0.33Mn0.33O2 and LiFePO4 positive electrodes

The influence of two types of multi-walled carbon nanotubes, pristine (MWCNTs) and carboxylated (MWCNTs–COOH), on the electrochemical performance of LiNi0.33Co0.33Mn0.33O2 (NCM)- and LiFePO4 (LFP)-based positive electrodes is investigated. Several characterization techniques, e.g., electronic conductivity measurements, galvanostatic cycling, cyclic voltammetry, electrochemical impedance spectroscopy, and SEM/EDX, were employed. The results suggest that improved electronic conductivity is not necessarily synonymous with enhanced performance. A clear dependence of both rate capability and electrode morphology on the combination of conductive additive and active material can be observed. In particular, while LFP performs better with MWCNTs–COOH, pristine MWCNTs appear to be better suited for NCM. Although the use of MWCNTs–COOH improves the connective network between the active particles for both NCM and LFP, the presence of COOH moieties appears to have a strong effect on the surface properties of the NCM-based electrodes. MWCNTs–COOH formed a shell around the active particles, which may function as a physical barrier and hinder Li+ insertion/extraction.

Synthesis of N4 donor macrocyclic Schiff base ligands and their Ru (II), Pd (II), Pt (II) metal complexes for biological studies and catalytic oxidation of didanosine in pharmaceuticals

A series of tetraaza (N4 donor) macrocyclic ligands (L1–L4) were derived from the condensation of o-phthalaldehyde (OPA) with some substituted aromatic amines/azide, and subsequently used to synthesize the metal complexes of Ru(II), Pd(II) and Pt(II). The structures of macrocyclic ligands and their metal complexes were characterized by elemental analyses, IR, 1H &13C NMR, mass and electronic spectroscopy, thermal, magnetic and conductance measurements. Both the ligands and their complexes were screened for their antibacterial activities against Gram positive and Gram negative bacteria by MIC method. Besides, these macrocyclic complexes were investigated as catalysts in the oxidation of pharmaceutical drug didanosine. The oxidized products were further treated with sulphanilic acid to develop the colored products to determine by spectrophotometrically. The current oxidation method is an environmentally friendly, simple to set-up, requires short reaction time, produces high yields and does not require co-oxidant.

Electronic conductivity of Ni-doped yttria-stabilized zirconia

The electronic conductivity of (NiO)0.01[(Y2O3)0.08(ZrO2)0.92]0.99 was measured with a modified ion blocking method at 1273K in the oxygen partial pressure (p(O2)) range of 10−3–10−17MPa. At p(O2)>10−6 and <10−14MPa, the electronic conductivity was proportional to the 1/4 and −1/4 power of p(O2) due to hole and electron conduction, respectively. The electron conductivity was obviously smaller for Ni-doped YSZ than for YSZ by a factor of 2.0 at p(O2) range of 10−14–10−17MPa. The measured electronic conductivity of Ni-doped YSZ was used to calculate the oxygen potential distribution in the electrolyte under the ion blocking condition. The lower oxygen potential region in the electrolyte was in excellent agreement with the darkly colored region found in the Ni-doped YSZ electrolyte after the electronic conductivity measurements.

Ni–BaCe0.95Tb0.05O3−δ cermet membranes for hydrogen permeation

BaCe0.95Tb0.05O3−δ (BCTb) proton conducting perovskite powders were first synthesized via an EDTA–CA complexing method. Ni–BCTb cermet membranes were then fabricated by pressing a mixture of the BCTb and Ni powders in a weight ratio of 1:1 at 10 MPa, followed by sintering at 1400 °C for 10 h. The properties of the BCTb powders and the Ni–BCTb membranes were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and conductivity measurement using a 4-probe method. The electrical conductivity of the Ni–BCTb membranes approaches to 400 S cm−1 at room temperature but decreases with increasing temperatures. The maximum hydrogen permeation flux through the asymmetric Ni–BCTb membrane with a 90 μm separation top layer integrated with a porous substrate has reached up to 0.914 mL (STP) cm−2 min−1 at 850 °C when using the 50% H2/N2 mixture feed and He as the sweep gas, respectively. The surface exchange reaction kinetics takes a controlling effect on the hydrogen permeation through the membrane. The long-term operation test indicates that the Ni–BCTb cermet membranes are not sufficiently stable for hydrogen permeation due to the phase decomposition of the BCTb perovskite.

A novel method to enhance rate performance of an Al-doped Li4Ti5O12 electrode by post-synthesis treatment in liquid formaldehyde at room temperature

An amenable method for improving rate performance of Li4Ti4.85Al0.15O12 electrode by post-synthesis treatment in formaldehyde aqueous solution at room temperature is introduced. The as-prepared samples are characterized by XRD, BET, SEM, HR-TEM, XPS and electronic conductivity measurement. The treatment causes no noticeable change on the phase structure and has only little effect on the specific surface area and particulate morphologies. It also only slightly decreases the lithium ion diffusion coefficient. However, it substantially increases the electronic conductivity due to the creation of Ti3+ in the oxide lattice. The post-synthesis treatment for a period of 4 h effectively increases the capacity at 10 C rate for Li4Ti4.85Al0.15O12 from 125 mA h g−1 for the untreated sample to 160 mA h g−1, and the electrode performance is also fairly stable. This method is highly attractive for synthesis of high-performance Li4Ti5O12 electrodes owing to its simplicity, energy saving and efficiency. As a general method, post-synthesis treatment using formaldehyde may be applicable to other electrodes.

Electronic conductivity of alkyne-capped ruthenium nanoparticles

Ruthenium nanoparticles (2.12 ± 0.72 nm in diameter) were stabilized by the self-assembly of alkyne molecules (from 1-hexyne to 1-hexadecyne) onto the Ru surface by virtue of the formation of Ru-vinylidene interfacial linkages. Infrared measurements depicted three vibrational bands at 2050 cm(-1), 1980 cm(-1) and 1950 cm(-1), which were ascribed to the vibrational stretches of the terminal triple bonds that were bound onto the nanoparticle surface. Thermogravimetric analysis showed that there were about 65 to 96 alkyne ligands per nanoparticle (depending on the ligand chainlength), corresponding to a molecular footprint of 20 to 15 Å(2). This suggests that the ligands likely adopted a head-on configuration on the nanoparticle surface, consistent with a vinylidene bonding linkage due to interfacial tautomeric rearrangements. With this conjugated interfacial bonding interaction, electronic conductivity measurements of the corresponding nanoparticle solid films showed that the nanoparticles all exhibited linear current-potential curves within the potential range of -0.8 V to +0.8 V at varied temperatures (200 to 300 K). The ohmic characters were partly ascribed to the spilling of core electrons into the organic capping layer that facilitated interparticle charge transfer. Furthermore, based on the temperature dependence of the nanoparticle electronic conductivity, the activation energy for interparticle charge transfer was estimated to be in the range of 70 to 90 meV and significantly, the coupling coefficient (β) was found to be 0.31 Å(-1) for nanoparticles stabilized by short-chain alkynes (1-hexyne, 1-octyne, and 1-decyne), and 1.44 Å(-1) for those with long alkynes such as 1-dodecyne, 1-tetradecyne, and 1-hexadecyne. This may be accounted for by the relative contributions of the conjugated metal-ligand interfacial bonding interactions versus the saturated aliphatic backbones of the alkyne ligands to the control of interparticle charge transfer.

Synthesis, characterization and electrical proprieties study of layered benzyltrimethylammonium–vanadium pentoxide nanocomposites

Plate-like benzyltrimethylammonium-vanadium pentoxide intercalate compound have been synthesized by hydrothermal method. X-ray diffraction, scanning electron microscopy, transmission electron microscopy, thermal analysis techniques, and Raman spectroscopy have been used to characterize the structure, morphology and composition of the plates. The material has a layered structure with an interlayer spacing of about 1.369 nm. The width of the plates varies between 80 and 250 nm and a thickness around 40 nm. The influences of the reaction time on the morphology have been investigated. The electronic conductivity measurements show that the conductivity curve is described by an Arrhenius law with activation energy of 0.46 eV.