Metal-like Electrical Conductivity Research Articles

Effect of AuNP-AuNP vdW interaction on the mechanics and piezoresistivity of AuNP-polymer nanocomposite

Gold nanoparticle (AuNP)-polymer composite has attracted considerable attention due to its high stretchability, metal-like electrical conductivity and substantial piezoresistivity. In the nanocomposite, the effect of the van der Waals (vdW) interaction increases greatly between AuNPs, which may significantly change its overall mechanical and electrical properties. In examining this issue, the nanocomposite with randomly distributed AuNPs is constructed by Monte Carlo method, tensile tests on the material are then performed via molecular dynamics simulations and finally, its piezo-resistivity is studied based on an effective resistor model. The effects of AuNP interaction are examined for the mechanics, dynamics and piezoresistivity of the nanocomposite by comparing the results obtained in the presence and absence of the vdW interaction. It is found that the AuNP attraction tends to hold the AuNPs together, leading to enhanced Young’s modulus, yield and fracture stress even at the low volume fraction 5% to 10% of AuNPs. The piezoresistive effect of the composite is also improved as the AuNP attraction substantially affects AuNP dynamics in large deformation. It is expected that similar effects of NP vdW interaction can also be obtained for the nanocomposites based on copper or silver NPs embedded in polymer.

High thermoelectric power factor of ytterbium silicon-germanium

Metal silicide-based thermoelectric (TE) materials have attracted attention owing to low toxicity and high chemical stability. Here, we demonstrate that ytterbium silicon-germanium, Yb(Si1−xGex)2−δ, shows a large Seebeck coefficient (S) accompanied by metal-like high electrical conductivity (σ) attributed to the intermediate valence behavior of Yb (Yb2+/Yb3+). We revealed that x = 0.5, i.e., YbSiGe, is the best composition with the highest power factor (S2σ) of 3.6 mW m−1 K−2 at room temperature, which is comparable to those of conventional TE materials, such as Bi2Te3.

Polymer nanofibre composite nonwovens with metal-like electrical conductivity

Bendable and breathable polymer nanofibre nonwovens with metal-like electrical conductivity are required for lightweight electrodes and electric shielding design with applications in batteries, functional textiles, sensors, cars, aerospace, constructions, mobile phones, and medical devices. Metal-like conductivity in polymer nonwovens has not been achieved till now due to the limitation of the existing processing techniques. We show here, the metal-like electrical conductivity of 750,000 S/m in polyacrylonitrile (PAN), poly(ε-caprolactone) (PCL) nonwoven using very low content of silver nanowires (AgNW; 3.35 vol%). The key to the high conductivity was the homogenous distribution of AgNW in nonwoven made by wet-laid process using short electrospun fibre and AgNW dispersion. Above a threshold of 0.36 vol% AgNW, the conductivity of the nonwoven increased by seven orders of magnitude, which we attribute to the onset of percolation of the AgNW. Our nonwoven-AgNW composites show fast heating and cooling within a few seconds at a voltage of 1.1 V, which is in the range of portable devices. These composites are also breathable and bendable. The electrical conductivity was independent of the bending angle of the composite, which is important for applications mentioned above and would help other scientists to design new conductive materials in the future.

Electrochemical Fabrication of MoO2/MoO3-Based Photo-Anodes for Water Splitting

After Fujishima and Honda reported their results on the photo-electrolysis of water [1], three materials have received special attention for the fabrication of photo-anodes: (i) titanium dioxide (TiO2), (ii) hematite (α-Fe2O3) and (iii) tungsten trioxide (WO3). These materials present high efficiencies for solar energy capture and conversion to chemical energy, stability under water splitting operating conditions and/or low cost and earth abundance [2]. However, when operating under illumination in the visible range (ca. 45% of the solar spectrum), these semiconductors need of an external potential (bias) to promote the oxygen evolution reaction on its surface, due to the position of their conduction and valence bands [3]. In this context, it has been observed that molybdenum trioxide (MoO3) films have good electrochromic and photochromic properties, while molybdenum dioxide (MoO2) has an unusual metal-like electrical conductivity [4,5]. Therefore, these compounds emerge as an interesting alternative for the fabrication of photo-anodes for water splitting. Photo-anodes are usually fabricated by coating or electrodepositing films of the photo-active material on a substrate (e.g. fluorine-doped tin dioxide(FTO)-coated glass) that acts as current collector and support. The technique chosen has to allow a good control of the structural parameters (particle size, crystallinity and thickness) of the photo-active films produced, since they will affect the photo-electrochemical behavior of the cell [6]. Furthermore, if the photo-anodes are to be produced on a large scale, the production rate and the reproducibility that the fabrication technique offers is crucial. Electrochemical coating processes have been applied successfully in industry for decades. Therefore, this research project aims to produce photo-anodes for water splitting by electrodeposition of MoO2/MoO3 thin films on FTO-coated glass. Fabrication of MoO2/MoO3-based photo-anodes was carried out by applying a potential of -1.377 V vs Ag/AgCl (3 M KCl) during 3 hours on an FTO-coated glass working electrode immersed in a solution containing 0.075 M molybdenum trioxide (MoO3), 0.075 M nickel sulfate (NiSO4·6H2O), 0.5 M tri-sodium citrate (Na3C6H5O7·2H2O) and 0.7 M ammonium hydroxide (NH4OH). The MoO2/MoO3 films produced are ca. 2.3 μm thick, present an irregular microstructure (determined using scanning electron microscopy, SEM) and show a dark brown pigmentation, typical of molybdenum oxides. X-ray photoelectron spectroscopy (XPS) analysis of the samples determined that these films contain molybdenum in at least two different oxidation states (IV and VI), possibly forming MoO2 and MoO3. These results are in good agreement with the energy dispersive X-ray spectroscopy (EDX) analysis of the samples, which showed that the films produced contain approximately 33.7% in weight of molybdenum. Finally, a Tauc plot (Figure 1) was generated using the UV-visible absorption spectra of the samples, which determined that the photo-anodes fabricated present an allowed direct band gap of 2.6 eV. The anodes photo-activity for oxygen evolution was studied by cyclic voltammetry using an electrochemical cell with a 0.1 M Na2SO4 solution as electrolyte. The results obtained (Figure 2) show that in the dark the oxygen evolution reaction on the surface of the MoO2/MoO3-based photo-anodes is triggered at ca. 1.2 V vs Ag/AgCl (3 M KCl), while under UV illumination (wavelength = 364 nm) this phenomenon occurs at ca. 0.6 V vs Ag/AgCl (3M KCl). From the results exposed before, it is clear that the photo-anodes produced present interesting semiconducting and catalytic properties for their application in an electrochemical cell for water splitting. Consequently, future work will be centered in the design and fabrication of a photo-electrochemical cell using these electrodes and improvements will be introduced by heat treatment or doping of the electrodeposited MoO2/MoO3 films. ACKNOWLEDGMENTS The authors thank the Chilean Government for a CONICYT studentship for MGG. REFERENCES Fujishima, A. and Honda, K. (1972). Electrochemical photolysis of water at a semiconductor electrode. Nature, 238, 37-38.Ong, CK. (2013). Design and performance of photo-electrochemical reactors with Fe2O3 photo-anodes for water splitting. PhD thesis, Imperial College London.Xu, Y. and Schoonen, M. (2000). The absolute energy positions of conduction and valence bands of selected semiconducting minerals. American Mineralogist, 85, 543-556.Al-Kandari, H., Mohamed, AM., Al-Kharafi, F., Zaki, MI. and Katrib, A. (2012). Modification of the catalytic properties of MoO2−x(OH)y dispersed on TiO2 by Pt and Cs additives. Applied Catalysis A: General, 417, 298-305.Dukstiene, N., Sinkeviciute, D. and Guobiene, A. (2012). Morphological, structural and optical properties of MoO2 films electrodeposited on SnO2∣glass plate. Central European Journal of Chemistry, 10, 1106-1118.Krol, R. and Grätzel, M. (2012). Photoelectrochemical Hydrogen Production. Springer, Nueva York. Figure 1

Metal-like electrical conductivity in LaxSr2-xTiMoO6 oxides for high temperature thermoelectric power generation.

Increasing electrical conductivity in oxides, which are inherently insulators, can be a potential route in developing oxide-based thermoelectric power generators with higher energy conversion efficiency. In the present work, environmentally friendly non-toxic double perovskite LaxSr2-xTiMoO6 (LSTM) ceramics were synthesized using a solid-state reaction route by optimizing the sintering temperature and atmosphere for high temperature thermoelectric applications. Rietveld refinement of XRD data confirmed a single-phase solid solution with a cubic structure in these double perovskites with the space-group Pm3[combining macron]m. SEM studies showed a highly dense microstructure in these ceramics. High electrical conductivity on the order of 105 S m-1 and large carrier concentration (∼1022 cm-3) were obtained in these materials. The temperature-dependent electrical conductivity measurement showed that the LSTM ceramics exhibit a semiconductor to metal transition. Thermopower (S) measurements demonstrated the conductivity switching from a p-type to n-type behavior at higher temperature. A temperature dependent Seebeck coefficient was further explained using a model for coexistence of both types of charge carriers in these oxides. A conductivity mechanism of these double perovskites was found to be governed by a small polaron hopping model.

ChemInform Abstract: Organic‐Inorganic Hybrids: From Magnetic Perovskite Metal(II) Halides to Multifunctional Metal(II) Phosphonates

AbstractReview: 108 refs.

Suitability of layered Ti3SiC2 and Zr3[Al(si)]4C6 ceramics as high temperature solar absorbers for solar energy applications

Layered Ti3SiC2 and Zr3[Al(Si)]4C6 ceramics were prepared by hot-pressed sintering. The spectrally selective absorption properties of these layered carbides have been investigated and compared with those of TiC and ZrC. It is found that the Ti3SiC2 ceramic exhibits a solar absorbance of 0.70 and a thermal emissivity of 0.19, yielding spectral selectivity (absorbance divide by emissivity) of 3.7, while the spectral selectivity of Zr3[Al(Si)]4C6 is 2.8 (0.71/0.25). To evaluate the suitability of these ceramics as high-temperature absorbers for solar radiation, the investigation on the thermal stability and temperature dependent emittance was performed in air. Compared with TiC and ZrC, both Ti3SiC2 and Zr3[Al(Si)]4C6 show better thermal stability. Meanwhile, Ti3SiC2 and Zr3[Al(Si)]4C6 exhibit a low emissivity in the investigated temperature range, benefiting from their metal-like electrical conductivity.

Zr2Fe12As7 and Hf2+xFe12−yAs7 with Zr2Fe12P7 type structure: Iron arsenides with layered sections from LiFeAs structure

The new compound Zr2Fe12As7 was prepared from the elements at 1110 °C. Zr2Fe12As7 crystallizes in the hexagonal Zr2Fe12P7 structure type (space group P6¯, a = 952.10(7) pm, c = 373.24(2) pm, V = 293.01 · 106 pm³, R1 = 0.031, wR2 = 0.077) with one formula unit in the hexagonal unit cell. The structure can be viewed as formed by chemical twinning from slabs occurring in many superconducting alkali, alkaline-earth and rare-earth metal iron pnictides. Zr2Fe12As7 shows Curie-paramagnetism and a metal-like electrical conductivity. The formation and particularly crystal growth of an analogues Hf compound requires higher temperatures of 1350 °C, which additionally provoke partial substitution of Fe by Hf in Hf2+xFe12–yAs7 (x = 1.6(2), y = 3, space group P6¯, a = 951.1(1) pm, c = 370.39(3) pm, V = 290.17 · 106 pm³, R1 = 0.044, wR2 = 0.097).

Transient metal-like electrical conductivity in swift heavy ion irradiated insulators

The irradiation of insulators with swift heavy ions leads to a transient excitation of valence band electrons into the targets conduction band. The population of the conduction band gives rise to an increased electrical conductivity of the intrinsically non-conductive insulator. Due to the transient nature of the number density of excited electrons in the conduction band, the electrical conductivity is also strongly time dependent. In this work it is demonstrated how the transient electrical conductivity can be evaluated on the basis of a combination of the Monte Carlo method and a two temperature model. As a model system, the irradiation of SiO2 with 11.4MeV/u Ca ions, corresponding to a stopping power of dE/dx=2.7keV/nm, is chosen for the calculations. It is found, that the enhancement of the electrical conductivity is quite large and comparable to that of metals like gold. The striking magnitude of this enhancement may allow for an experimental measurement of the electrical conductivity of insulators during irradiation with swift heavy ions.

Combinatorial investigation of the stoichiometry, electronic transport and elastic properties of (Cr 1−xV x) 2GeC thin films

We report on a combinatorial investigation of (Cr,V)–Ge–C via films grown by magnetron sputtering with a focus on the (Cr 1− x V x ) 2 GeC region. Deviations from Vegard’s law for (Cr 1− x V x ) 2 GeC suggest that there can be deficiencies in C in Cr-rich films. All compositions showed metal-like electrical conductivity which was significantly influenced by solid-solution scattering, and the temperature coefficient of resistivity provides an indirect probe of the electronic density of states. Raman spectroscopy indicated that alloying has minimal effect on the elastic moduli.

The Chemistry of Cadmium–Thiocarboxylate Derivatives: Synthesis, Structural Features, and Application As Single Source Precursors for Ternary Sulfides

Novel heterobimetallic complexes [(PPh(3))(2)Cu(μ-SCOPh)(2)Cd(SCOPh)] (2a), [(PPh(3))(2)Cu(μ-SCOth)(2)Cd(SCOth)] (2b), [(PPh(3))(2)Ag(μ-SCOth)(2)Cd(SCOth)] (3a), [(PPh(3))(2)Ag(μ-SCOth)(2)Cd(H(2)O)(SCOth)] (3b), [(PPh(3))(2)Ag(μ-SCOPh)(2)Cd(SCOPh)] (3c), and a bimetallic complex [PPh(3)Cd(μ-SCOth)SCOth](2)·CH(2)Cl(2) (5) (th = thiophene) were prepared and characterized by single crystal X-ray diffraction analysis. A coordination polymer [Cd(SCOPh)(2)](n) (4) has also been characterized structurally that exhibited metal-like electrical conductivity. The heterobimetallic complexes on pyrolyzing under controlled conditions yielded ternary sulfides of composition CuCd(7)S(8), CuCd(10)S(11), Ag(2)Cd(8)S(9), and Ag(2)Cd(5)S(6), which have been characterized by SEM-EDX and X-ray diffractometry. Photophysical properties and electrical conductivities of the sulfides have also been studied.

Synthesis and applications of molybdenum (IV) oxide

Molybdenum dioxide (MoO2) is a transition metal oxide with unusual metal-like electrical conductivity and high catalytic activity toward reforming hydrocarbons. This review covers the synthesis techniques used to fabricate MoO2 in a variety of morphologies and particle sizes. Processing from molybdenum ore and reduction from MoO3 are also covered, with emphasis on reduction mechanisms and kinetic considerations. Discussions of various solution-based and gas phase synthesis techniques shed light on strategies to achieve various unique morphologies, which leads into a brief discussion of nanoscale MoO2. Nanoscale MoO2 is of interest for important technological applications including catalysts for partial oxidation of hydrocarbons, solid oxide fuel cell anodes, and high-capacity reversible lithium ion battery anodes.

Synthesis of Ti3SiC2 by Pressureless Sintering of Compacted Powder Blends of Ti, SiC, C and TiC

Titanium silicon carbide Ti3SiC2, a member of MAX-phase ternary compound ceramics, is expected as a new resistance heating element substituting for conventional ones including rare metals because of its excellent high-temperature oxidation resistance, metal-like electrical conductivity, good machinability and ubiquitous constituent elements. The authors tried to synthesize a large bulk Ti3SiC2 by pressureless sintering of a compacted powder blend of Ti, SiC and C, while the powder compact collapsed during sintering. Causes of the collapse were investigated and based on the investigation results a solution for the problem was found out. The large bulk Ti3SiC2 was synthesized successfully without collapse by the replacement of a part of Ti and C in the starting powders with TiC.

Magnetite at low temperature: Resonant inelastic x-ray scattering (RIXS) at the Fe K-edge

At room temperature, magnetite (cubic inverse spinel structure, Fd-3m s.g.) shows metal-like electrical conductivity, which discontinuously drops by two orders of magnitude below ca. 120 K (Tv). This is due to a first-order phase transition, where the cubic structure is distorted to monoclinic symmetry (Cc s.g.). Models for this metal-insulator transition are still highly debated. We performed 1s3p as well 1s2p RIXS measurements well below and above Tv on a sample of synthetic magnetite powder to probe any difference present in the electronic states. Neither 1s3p nor 1s2p RIXS spectra reveal any differences between the two phases. Our observations are consistent with earlier EXAFS data and indicate no changes in the local structural geometry around Fe.

Metal-like electrical conductivity in ceramic nano-composite

The addition of TiO 2 improves the densification of amorphous silicon carbonitride powder, making possible the preparation of Si 3N 4/SiC/TiC 0.3N 0.7 nano-ceramics with attractive mechanical properties and a high electrical conductivity.

Production and characterisation of vapour grown carbon fiber/polypropylene composites

Polymeric composites are widely used in the aircraft and automotive industries. Their high strength-to-weight ratio makes significant weight reduction possible. Beside this advantage, the polymer materials also offer a good corrosion resistance but the mechanical and electrical properties are not satisfactory. In order to increase these properties, vapour grown carbon fibers (VGCF) with high strength and metal-like electrical conductivity can be embedded in the polymeric matrix. To ensure a good adhesion between the fibers and the polymer matrix a functionalization of the chemically inert surface of the fibers is necessary. In the present research work oxygen-containing functional groups were introduced on the fiber surface through cold plasma treatment. Measurements of the fiber surface energy after plasma functionalization showed an enhancement of at least 50% of the initial value. The VGCF/PP composites with different amounts of VGCF were made through extrusion and injection molding. The results show that the degree of fiber surface functionalization and the fiber distribution and orientation in the polypropylene (PP) matrix may strongly influence the mechanical properties of the composite.

New electroconducting transparent films: Amorphous copper sulfide and its iodine-doped derivative

A reaction between [Cu(cyclam)] 2+ (cyclam: 1,4,8,11-tetraazacyclotetradecane) and sodium sulfide gave a polyethylene-supported CuS film, which was transparent and exhibited metal-like electrical conductivity down to 250 K. An electrode fabricated with this film showed Nerstian behavior versus a Ag/AgCl electrode, for Cu 2+ solutions in the concentration range C Cu = 5·10 −5−10 −2 M. The CuS film was doped with iodine, the temperature range of its metal-like charge-transport behavior was extended down to 140 K. The X-ray photoelectron spectra showed that CuS coexisted with CuI which was formed upon doping. These results suggest that the CuS film can be used in the fabrication of electrical and electronic devices and that the physical properties of the film can be controlled by doping.

Synthesis and Properties of a New Kind of One-Dimensional Conductors. 2. Extended Hückel Calculations on the Energy Band Structure

Abstract The co-ordination polymer of tetrazaporphin (TAP) with a transition metal, say FeII , in its center and acetylide anion, C2 2⊖ , as an axial bidentate bridging ligand is taken as a model sub-stance for the new type of one-dimensional conductors introduced in the preceding communication of this series. Although the monomer shows D4h symmetry, this is reduced to C4v for arbitrary kz -values of the Bloch functions of the first Brillouin zone. From the irreducible representations a1, a2, b1, b2, and e only a1 and e have contributions from all components, namely TAP2⊖ , Fe2⊕ and C2 2⊖, so that for these races broad energy bands can be expected. The a2, b1, and b2 MOs of the TAP-FeII subunits are separated fairly well and have no counterparts in the C2 2⊖ bridges so that very narrow bands should arise. This is confirmed by an EH calculation. Unexpectedly the a1 bonds which have contributions from the σ-MOS of C2 2⊖ are broader than the e-bands which contain the two crossed π-MO systems of C2 2⊖ . The quantitative results of the nearly self-consistent iterative EH calculation indicate overlap of the energy bands near the Fermi level and fulfill thus one necessary condition for metal-like electrical conductivity.