The preparation of and electrical properties of niobium selenide and tungsten selenide

Kershaw, R.; Vlasse, Marcus; Wold, A.

doi:10.1021/ic50054a043

Cited by 129 publications

(29 citation statements)

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“…The mixtures were heated with 15 K h Ϫ1 to 873 K held at this temperature for two days, heated with 15 K h Ϫ1 to 1073 K, held for another two days at this temperature and cooled slowly down to room temperature [12]. NbS 2 and TaS 2 were obtained from the stoichiometric mixture of the elements.…”

Section: Methodsmentioning

confidence: 99%

Syntheses and Crystal Structures of a New Niobium Polysulfide K6Nb4S22 and two New Dimorphic Tantalum Polysulfides K6Ta4S22

Stoll

Näther

Bensch

2002

Z. anorg. allg. Chem.

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The new compounds K 6 Nb 4 S 22 and K 6 Ta 4 S 22 (I) have been synthesised by the reaction of NbS 2 or Ta metal in a K 2 S 3 flux. Using TaS 2 as educt a second modification of K 6 Ta 4 S 22 (II) is obtained. K 6 Nb 4 S 22 and K 6 Ta 4 S 22 (form I) crystallise in the monoclinic space group C2/c with a ϭ 35.634 (2) Å , b ϭ 7.8448 (4) Å , c ϭ 12.1505 (5) Å , β ϭ 100.853 (5)°, V ϭ 3335.8 (3) Å 3 , and Z ϭ 4 for K 6 Nb 4 S 22 and a ϭ 35.563 (7) Å , b ϭ 7.836 (2) Å , c ϭ 12.139 (2) Å , β ϭ 100.56 (3)°, V ϭ 3325.5 (2) Å 3 , and Z ϭ 4 for K 6 Ta 4 S 22 (I). The second modification K 6 Ta 4 S 22 (form II) crystallises in the monoclinic space group P2 1 /c with a ϭ 7.5835 (6) Å , b ϭ 8.7115 (5) Å , c ϭ 24.421 (2) Å , β ϭ 98.733 (9)°, V ϭ 1594.6 (2) Å 3 , and Z ϭ 2. The structures consist of [M 4 S 22 ] 6Ϫ anions composed of two M 2 S 11 sub-units which are linked into M 4 S 22 units via terminal sulfur ligands. The anions are well separated by the

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Section: Methodsmentioning

confidence: 99%

Syntheses and Crystal Structures of a New Niobium Polysulfide K6Nb4S22 and two New Dimorphic Tantalum Polysulfides K6Ta4S22

Stoll

Näther

Bensch

2002

Z. anorg. allg. Chem.

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“…Large single crystals of WS~ were prepared by chemical transport using a concentration of 5 rag/ cm 8 of bromine as the transporting agent. A melting point capillary containing the calculated weight of bromine was sealed at a pressure of 10-s Tort and placed in an H-tube filling apparatus (16). Stoichiometric quantities of tungsten and sulfur were added, and the apparatus was evacuated to 10 -5 Tort and sealed off.…”

Section: Methodsmentioning

confidence: 99%

Characterization of n-Type Semiconducting Tungsten Disulfide Photoanodes in Aqueous and Nonaqueous Electrolyte Solutions

Baglio¹

1982

J. Electrochem. Soc.

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Synthetic, single crystal, n-type semiconducting WS2 (bandgap ~ 1.3 eV) has been characterized as a photoanode in aqueous and nonaqueous electrolyte media. The WS2 was synthesized from the elements by bromine and chlorine transport to yield plates up to 3 • 3 mm in dimension. Interface characterization includes (i) cyclic voltammetry in the presence of a large number of fast, one-electron redox couples in CH3CN/0.1M [n-Bu4N]C104 solutions; (ii) steadystate photocurrent-voltage properties in aqueous and nonaqueous solutions of X-(X-= CI-, Br-, I-); (iii) tests of durability; (iv) wavelength dependence of photocurrent and photovoltage; and (v) high resolution (-5 t~m) laser mapping of the surface to reveal surface inhomogeneity with respect to output photovoltage. Highlights of the results are: (i) n-type WS2 is durable in aqueous electrolytes containing high concentrations of X-to yield efficient visible lightassisted oxidation of X-; e.g., C1---~ 1/2 C12 has up to 6.9% and Br--~ 1/2 Br2 up to 12% efficiency at a 632.8 nm input power of 16 mW/cm2; (ii) in aqueous, but not nonaqueous, solutions I-adsorbs such that the onset of photocurrent is shifted several hundred millivolts as for other metal dichalcogenide photoanodes; the shift is sufficient that visible light can be used to sustain the conversion of 2HI to H2 and I2 with no other energy input; (iii) cyclic voltammetry in CH3CN/0.1M [n-Bu4N]C104 for a number of redox couples shows that a photovoltage of up to -0.7V is possible; photovoltage varies from 0.0 to -0.7V for redox couples having E,~ from -0.0V vs. SCE to -+0.8V while the photovoltage is fixed at -0.7V for E,2's more positive than -+0.8V vs. SCE; (iv) efficiency for halogen generation in aqueous solutions generally exceeds efficiency in CH3CN solutions; and (v) the diffusion length of holes parallel to the surface is -200 ~m which explains the dramatic influence of the steps on the recombination of carriers on layered compounds.Metal dichalcogenides have been shown to be relatively durable and efficient photoanode materials for use in photoelectrochemical cells for conversion of visible light to electricity or to chemical energy in the form of oxidation and reduction products (1-7). The materials MoS2, WSe2, and MoSe~ have received most attention, but there are a number of other metal dichalcogenide ,materials that might serve as durable and efficient photoanodes. One of the intriguing findings concerning WSe2 is that it is an anode material * Electrochemical Society Active Member.t Electrochemical Society Student Member.

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“…at some of the chosen dc fields H dc (0 to 2 kOe) in three crystals X, Y and Z of 2H-NbSe 2 . These crystals were grown by the same vapor transport method [19], but with starting materials of different purity such that the specimen X is the cleanest among the three and the specimen Z, the most disordered. The relative purity of the three crystals is reflected in the width of the superconducting transition in χ ′ (t) response in zero field, which can be seen to progressively enhance in Figs.…”

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confidence: 99%

Re-entrant peak effect in an anisotropic superconductor 2H − NbSe ₂ : Role of disorder

et al. 1998

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The reentrant nature of the Peak Effect (PE) is established in a single crystal of anisotropic superconductor 2H-NbSe2 via electrical transport and dc magnetization studies. The role of disorder on the reentrant branch of the PE has been examined in three single crystals with varying levels of quenched random disorder. Increasing disorder presumably shrinks the (H,T) parameter space over which vortex array retains spatial order. Although, the upper branch of the PE curve is somewhat robust, the lower reentrant branch of the same curve is strongly affected by disorder.

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The preparation of and electrical properties of niobium selenide and tungsten selenide

Cited by 129 publications

References 4 publications

Syntheses and Crystal Structures of a New Niobium Polysulfide K6Nb4S22 and two New Dimorphic Tantalum Polysulfides K6Ta4S22

Syntheses and Crystal Structures of a New Niobium Polysulfide K6Nb4S22 and two New Dimorphic Tantalum Polysulfides K6Ta4S22

Characterization of n-Type Semiconducting Tungsten Disulfide Photoanodes in Aqueous and Nonaqueous Electrolyte Solutions

Re-entrant peak effect in an anisotropic superconductor 2H − NbSe ₂ : Role of disorder

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The preparation of and electrical properties of niobium selenide and tungsten selenide

Cited by 129 publications

References 4 publications

Syntheses and Crystal Structures of a New Niobium Polysulfide K6Nb4S22 and two New Dimorphic Tantalum Polysulfides K6Ta4S22

Syntheses and Crystal Structures of a New Niobium Polysulfide K6Nb4S22 and two New Dimorphic Tantalum Polysulfides K6Ta4S22

Characterization of n-Type Semiconducting Tungsten Disulfide Photoanodes in Aqueous and Nonaqueous Electrolyte Solutions

Re-entrant peak effect in an anisotropic superconductor 2H − NbSe 2 : Role of disorder

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Re-entrant peak effect in an anisotropic superconductor 2H − NbSe ₂ : Role of disorder