A. I. Romanenko

Effect of anion and cation substitution in tungsten disulfide and tungsten diselenide on conductivity and thermoelectric power

The temperature dependences of the conductivity and thermoelectric power for a series of samples W1–xNbxS2, W1–xNbxSe2, WS2–ySey, W1–xNbxS2–ySey are studied at low temperatures. It is found that the cation substitution of W atoms with Nb leads to an increase in the conductivity and a decrease in the thermoelectric power. The anion substitution of S with Se atoms results in a simultaneous increase in the conductivity and thermoelectric power. The highest power factor among the samples studied is inherent to W0.8Nb0.2Se2.

Electron transport properties of thermoelectrics based on layered substituted transition metal dichalcogenides

Temperature dependences of the electrical conductivity are studied in the range 4.2’300 K and Seebeck coefficient at room temperature of bulk samples of tungsten dichalcogenide polycrystals with niobium substitutions for tungsten and selenium substitutions for sulfur – W1–xNbx(S1–ySey)2. The two-dimensionalization of electron transport properties is detected at niobium concentrations x ≥ 0.1 in W1–xNbxS2 and x ≥ 0.05 in W1–xNbxSe2. In samples with additional partial selenium substitution for sulfur the electron transport remains three-dimensional. At room temperature the Seebeck coefficient (at equal electrical conductivities) is several times higher in the samples with quasi-two-dimensional transport than in the samples with three-dimensional transport. The calculation of the power factor at room temperature shows its nine times increase.

Control Conductance of Single Walled Carbon Nanotubes Films During Synthesis

Yaroslav A. Bryantsev∗ Nikolaev Institute of Inorganic Chemistry Lavrentiev, 3, Novosibirsk 630090 Novosibirsk State Technical University Marksa, 20, Novosibirsk, 630073 Russia Viacheslav E.Arhipov† Nikolaev Institute of Inorganic Chemistry Lavrentiev, 3, Novosibirsk 630090 Russia Anatoly I. Romanenko‡ Nikolaev Institute of Inorganic Chemistry Lavrentiev, 3, Novosibirsk 630090 National Research Tomsk State University Lenina, 36, Tomsk, 634050 Russia Alexander S. Berdinsky§ Novosibirsk State Technical University Marksa, 20, Novosibirsk, 630073 Russia Alexander V.Okotrub¶ Nikolaev Institute of Inorganic Chemistry Lavrentiev, 3, Novosibirsk 630090 Russia

The Research of Temperature Dependences of Electrical Conductivity and Thermopower of WS2 and WSe2 with Partial Replacement of W on Nb

The Research of Temperature Dependences of Electrical Conductivity and Thermopower of WS2 and WSe2 with Partial Replacement of W on Nb Galina E. Yakovleva∗ Nikolaev Institute of Inorganic Chemistry Lavrentiev, 3, Novosibirsk 630090, Russia Anatoly I. Romanenko† Nikolaev Institute of Inorganic Chemistry Lavrentiev, 3, Novosibirsk, 630090 National Research Tomsk State University Lenina, 36, Tomsk, 634050, Russia Alexander S. Berdinsky‡ Novosibirsk State Technical University Marksa, 20, Novosibirsk, 630073, Russia Vitalii A.Kuznetsov§ Nikolaev Institute of Inorganic Chemistry Lavrentiev, 3, Novosibirsk, 630090 Novosibirsk State Technical University Marksa, 20, Novosibirsk, 630073, Russia Alexandra Yu. Ledneva¶ Vladimir E. Fedorov∥ Nikolaev Institute of Inorganic Chemistry Lavrentiev, 3, Novosibirsk, 630090, Russia

Piezoresistive effect in composite films based on polybenzimidazole and few-layered graphene

The paper reports experimental study of piezoresistive effect in composite films based on polybenzimidazole with few-layered graphene nanoparticles filler. Colloidal dispersions of few-layered graphene (FLG) were obtained by ultrasonic treatment of synthesized FLG in the solution of poly[2,2′-(p-oxydiphenylen)-5,52′-bisbenzimidazole] (OPBI) in N-methyl-2-pyrrolidone (NMP). Electroconductive films were formed from the dispersions by flow coating. To investigate dependence of electrical resistance on mechanical strain strips of the films were bonded onto beams of uniform strength (in bending) with cyanoacrylate adhesive, the beams being insulated with polymer glue. The strain gauge factors were measured for two films with filler content being 0.75 and 2.00 mass per cent. Electrical resistances were measured by two- and four-point methods, the factors being independent on the method used. The factors are the same within the error for both filler contents and equal to 21 on average.

Tungsten dichalcogenides as possible gas-sensing elements

Possible application of tungsten dichalcogenides as gas-sensing elements is discussed in this paper. The experimental results on sensitivity of pristine and niobium doped WS2 and WSe2 to acetone and ethanol gases are presented. Polycrystalline powder specimens were obtained by high temperature solid-state synthesis from the stoichiometric mixture of pure elements. Two types of samples were studied: 1) tablets pressed at 1.5 GPa to form bulk samples and 2) thin films prepared from 35% ethanol-water colloidal dispersions by their filtration onto membrane filters (pore diameter is 20 nm). The electrical resistances of the samples were shown to be increased in the presence of ethanol and acetone gases at room temperature, thereby revealing positive response to reducing gases.

Thermoelectric properties of polycrystalline WS 2 with Nb replacement of metal atoms

The thermoelectric properties of polycrystalline materials on the base of WS2 with Nb partial replacement of metal atoms W have been researched in this work. The temperature characteristics of the materials have been measured in the temperature range from 77 to 300 K. We have found that replacement of metal atoms W partly with Nb significantly increases the electrical conductivity and decreases the Seebeck coefficient. The best stoichiometric ratio in terms of the thermoelectric properties has had material W0.90Nb0.10S2. This material has had a value of power factor 32 μW/m2·K.

Electron transport properties of polycrystalline tungsten-rhenium disulphide

The paper reports on electron transport properties of tungsten disulphide doped with rhenium: WS2, W0.95Re0.05S2, W0.90Re0.10S2 and W0.85Re0.15S2. Polycrystalline powders of the compositions were synthesized by direct high temperature reactions of elements with stoichiometric rations. Experimental samples were formed of the powders by conventional compress technology at a pressure of 1.5 GPa. The measured temperature dependences of conductivity are typical for fluctuation induced tunnelling conduction. The band gaps were estimated from the dependences and the gaps lie in the range from 100 to 400 meV for different compositions.

Thermoelectric properties of polycrystalline WS2 and solid solutions of WS2−ySey types

Transition metal chalcogenides are perspective thermoelectric materials which have a great interest for application. In this work, the polycrystalline bulk WS2 and solid solutions WS2-ySey types have been studied. In contrast to the literature data obtained at higher temperatures, we have investigated the thermoelectric properties of these materials at low and middle temperatures (77-450K). The temperature dependences of electrical conductivity and Seebeck coefficient were received from experimental data. The Seebeck coefficients of these materials have a high values, the maximum value up to 2000 μ V/K has been obtained.

The conductivity and TEMF of MoS 2 with Mo 2 S 3 additive

Transition-metal chalcogenides are prospective thermoelectric materials. One of them is a molybdenum disulfide MoS₂, which has a layered structure. MoS₂ has a good potential to have a high value of thermoelectric quality factor due to a high value of thermo-EMF and low value of thermal conductivity. But a low value of its electrical conductivity suppresses the thermoelectric quality factor ZT on the level of 0.1 at high temperatures. Present work shows the influence of metal addition to MoS₂ on electrical conductivity and Seebeck coefficient (SC) of final mixture. Mo₂S₃ was chosen as a metal addition. Mo₂S₃ has an electrical conductivity of 330 S/m and thermo-EMF of 10 μV/K at 300K. Bulk powder samples of MoS₂ with addition of 3, 6, 10, 30 and 60 wt% Mo₂S₃ were studied. An electrical conductivity of samples was measured in temperature range: 77 K - 423 K. All samples have shown semiconductor hopping conductivity with variable hopping length. The SC was measured in the temperature range of 300K - 500K. The addition of Mo₂S₃ decrease SC from 300μV/K to 75μV/K.