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Indium intercalation compounds of molybdenum disulphide; InxMoS2 (0⩽ × ⩽1)
Abstract
The present work reports a detailed investigation on crytal structure, electrical properties, and thermal stability for indium intercalation compounds of molybdenum disulphide. InxMoS2 (0⩽x⩽1). X-ray analyses show that intercalated compounds, like the host material 2HMoS2, also possess hexagonal symmetry with a small but continuous increase in interlayer spacing; there also exists a particle size anisotropy. Room temperature thermoelectric power experiments and low temperature (150 – 300 K) conductivity measurements indicate that intercalated compounds also exhibit n-type semiconducting behaviour similar to that of the base material MoS2. Thermal stability behaviour of these compounds in air and argon atmosphere has also been studied.
... The value of the electrical conductivity is in a range of 0.01 to 10 S/m at room temperature. The value of thermal conductivity is in a range of 0.1 to 1 W/(m*K) [5][6][7]. ...
Currently, transition metal disulfides have been used as promising non-noble metal based electrocatalysts in hydrogen evolution reaction (HER) from water splitting in quest of alternatives renewable and clean energy sources. In view of this, present work reports the fabrication of N and P co-doped exfoliated tungsten disulphide (PNEWS2) as a superior electrocatalyst in HER. The high performance of PNEWS2 in imparting significantly lower potential (59 mV) correspond to geometrical current density of 10 mA cm−2 and Tafel slope (35 mV per decade). This could be attributed to the presence of high active sites in the exfoliated single layered porous 1T-WS2 network and synergistic effect of N and P doping. Further, evalaution of durability tests suggested excellent stability of PNEWS2 catalysts. Our multifaceted strategy on formation of flake like 1T phase with expanded interlayer spacings of PNEWS2 catalyst compared to WS2 revealed presence of increase S active edges , sulpher vacancy and higher lifetime (0.239 ms) facilitating extremely high electrochemically active surface area (Cdl = 37.1 mF cm−2) and high turn over frequency (0.791 s-1). Further, density functional theory (DFT) calculations on downshifting of d band, metallic phase and lowest Gibbs free energy of hyrogen adsorbed on PNEWS2 account for its excellent mass transport property. We have also established that electrochemical performance of PNEWS2 is no way associated with the dissolution/redeposition of Platinum from counter electrode (Pt). In summary, superior performance of nonprecious promising N-P-co-doped WS2 provided an alternative substitute to Pt based electrocatalyst.
The fabrication and structure controlling of inorganic fullerene-like nanocompounds have attracted wide interests in recent years. A new approach of exfoliating-restacking-structure controlling was applied to overcome some technological problems in present preparation approaches. MoS2 and WS2 powders were used as precursor materials and exfoliated into single layers by butyllithium. The sample was treated by MnCl2 solution at 80°C to introduce Mn2+ cations into the reactive system. In this way, the single layer was restacked and the structure of product could be controlled. The products were characterized by XRD, TEM and HRTEM respectively. XRD results indicate that multimetal disulfide compounds can be fabricated by this new approach. TEM results show that the morphology of the multimetal disulfide compounds exhibits hollow-like nanotubes. HRTEM results show that the structure of the hollow-like nanotubes is of double layers. And the substructure of the inner layer exhibits multi-wall shape. Based on the above results, a possible formation mechanism of hollow multi-wall nanotubes was discussed.
Selenium powder and niobium powder were mixed at pre-set stoichiometric ratio and allowed to participate in solid phase reaction at 800°C affording NbSe2 powder. As-obtained NbSe2 powder was then mixed with Cu powder in the type of QMISP2 ball mill (rotation rate 200 r·min-1) by milling for 9 h. After drying they were put in the solid phase reaction kettle and allowed to participate in solid phase reaction at 800°C yielding Cu0.38NbSe2 powder. The phase composition and morphology of as-prepared Cu0.38NbSe2 powder were analyzed by means of X-ray diffraction(XRD) and scanning electron microscopy(SEM). In the meantime, the as-prepared Cu0.38NbSe2 powder was added in liquid paraffin as a lubricating oil additive, and its tribological properties were evaluated with a UMT-2 friction and wear tester. The results showed that Cu0.38NbSe2 still retained the hexagonal structure of NbSe2 matrix, but it was liable to agglomerate while its size increased as compared with that of NbSe2 matrix. Besides, it could be inferred that NbSe2 completely reacted with Cu matrix to generate intercalation compound CuxNbSe2 (0<x<0.66); and CuxNbSe2 showed poor tribological properties at low loads but excellent tribological properties at high loads, the mechanism of friction was explained. Moreover, the lubricating phase in NbSe2/Cu matrix composites was CuxNbSe2 rather than NbSe2.
During recent years, transition metal dichalcogenides of groups IVB, VB and VIB have received considerable attention because of the great diversity in their transport properties. 2H-WSe2 (Tungsten diselenide) is an interesting member of the transition metal dichalcogenide (TMDC's) family and known to be a semiconductor useful for photovoltaic and optoelectronic applications. The anisotropy usually observed in this diamagnetic semiconductor material is a result of the sandwich structure of Se–W–Se layers interacting with each other, loosely bonded by the weak Van der Waals forces. Recent efforts in studying the influence of the anisotropic electrical and optical properties of this layered-type transition metal dichalcogenides have been implemented by doping the samples with different alkali group elements. Unfortunately, little work is reported on doping of metals in WSe2. Therefore, it is proposed in this work to carry out a systematic growth of single crystals of WSe2 by doping it with copper in different proportions i.e. CuxWSe2 (x=0, 0.5, 1.0) by direct vapour transport technique. Transport properties like low and high temperature resistivity measurements, high pressure resistivity, Seebeck coefficient measurements at low temperature and Hall Effect at room temperature were studied in detail on all these samples. These measurements show that tungsten diselenide single crystals are p-type whereas doped with copper makes it n-type in nature. The results obtained and their implications are discussed in this paper.
Chemical methods for the exfoliation of transition metal dichalcogenides in a liquid medium to give single-layer dispersions containing quasi-two-dimensional layers of these compounds are surveyed. Data on the structure of dispersions and their use in the synthesis of various types of heterolayered intercalation compounds are discussed and described systematically. Structural features, the electronic structure and the physicochemical properties of the resulting intercalation compounds are considered. The potential of this method of synthesis is compared with that of traditional solid-state methods for the intercalation of layered crystals.
The sulphides and selenides of Mo and Ware layered compounds that possess a hexagonal strueture. The electronic structure of these layered transition metal dichalcogenide compounds, e.g. MoS2, WS2, MoSe2, WSe2, etc. [1-6], is of fundamental interest primarily because of the unusual crystal structure of these compounds. Within a layer the bonds are strong; while between adjacent layers, they are weak. As a result, the compounds exhibit marked anisotropy in most of their physical properties, which accounts for the great interest in this family of materials. The layer type structure also facilitates the process of intercalation by foreign metal atoms and organic and inorganic molecules, thereby allowing a convenient method of changing the strueture and electronic properties of the host crystals [7]. These compounds can form a wide fange of solid solutions, with either mixed metals or mixed chalcogenides [8, 9]. The main applications of these types of compounds are in hydrogen storage devices [7], in the field of catalysis [10], high temperature high pressure lubricants [1], long-life photochemical solar cells [11], etc. We have prepared a series of mixed metal-chalcogens solid solutions based on the Mo-W-S-Se quaternary system, Mo0.sW0.sSxSe2-x (0 ~< x ~< 2); whose characterization, thermal and magnetic behaviour have been reported earlier [12]. The aim of the present smdy is to determine some microstructural parameter, like particle size, r.m.s, strain, etc.; and, owing to the strong intralayer and weak interlayer forces, layer disorders are expected. We have thus calculated the variability of interlayer spacing, g, the fraction of planes affected by such defects, 7, and the dislocation density, p, etc. The estimations have been made using the method of variance, Fourier and integral width of the X-ray diffraction (XRD) line profiles of the (0 0 1) reflections. The compounds were synthesized directly from the elements, and the method of preparation is quite similar to that reported earlier [13]. The sample was then ground at room temperature (32 °C) by hand without any appreciable change in temperature and were passed through a 150 mesh sieve. The XRD intensities of the compounds were taken on a Philips 1729 diffractometer using CuKa radiation. Assuming that the broadening of the X-ray diffraction (XRD) line profile is due to presence of size broadening, strain broadening and broadening
Polycrystalline molybdenum disulphide has been grown by high pressure (about 54.88 × 106 N m−2) reduction of molybdenum trisulphide and characterized by various physicochemical methods. The chemical analysis of the compound established a sulphur to molybdenum ratio of 2, which was also confirmed by thermogravimetric analysis in air. The X-ray data was found to be consistent with 2H-MoS2, n-type conductivity (S = −275 μV °C−1) and diamagnetic behaviour ( c.g.s. e.m.u.). It is a semiconducting material with a room temperature conductivity of of and an activation energy of 0.124 eV in the temperature range 150–300 K. A band gap of 0.95 ± 0.02 eV was found from optical absorption studies on a thin MoS2 film. Thermal studies of MoS2 in an argon atmosphere has shown its stability up to 1200 °C and thereafter it decomposes to Mo2S3. A model has been proposed which describes the thermal behaviour of MoS2 when heated at various temperatures up to 1200 °C and is based on the appearance of lines in X-ray powder diffractogram of the product resulting from the crystallization of MoS2. Scanning electron microscope studies have also been made.
Optical absorption spectra of tungsten diselenide (WSe2) single crystals subjected to different values of pressure (0, 2, 4 and 6 GPa) were obtained in the spectral range 700–1450 nm with the help of a UV–VIS–NIR spectrophotometer. The spectra were thoroughly analyzed in the absorption edge region for obtaining direct as well as indirect band gaps in this material. The high temperature resistivity and thermoelectric power on WSe2 single crystals at various pressures were also studied. The results and their implications are discussed in the article.
The present paper deals with the preparation of tungsten-substituted molybdenum disulfide, Mo1−xWxS2 (0≤x≤1) compounds and their characterization by various physicochemical methods. X-ray studies confirmed that these compounds crystallized in a layer type of hexagonal structure. X-ray line profile analysis techniques such as the method of variance and Fourier analysis have been used for microstructural characterization of these compounds to find out information about particle size, r.m.s. strain, variability of interlayer spacing, fraction of planes affected by such defects, dislocation density, stacking fault probability and radial distribution function analysis for calculating coupling constants and mean-square displacements, etc. Room-temperature magnetic susceptibility measurements and thermoelectric power experiments and temperature variation of conductivity (25–350°C) confirmed, respectively, diamagnetic n- and p-type semiconducting behaviour for Mo1−xWxS2. Thermal stability behaviour of these compounds in air and inert atmosphere has also been carried out up to 1000°C. These studies indicated that the compounds are nearly stable up to 1000°C in inert atmosphere, whereas, in air, oxidative degradation of these compounds started at 400°C. The nature of the oxidized products has also been studied by X-ray analysis. Scanning electron micrograph studies are also reported here.
The present work deals with an investigation on synthesis, structure and properties of indium intercalation compounds of tungsten diselenide ; InxWSe2 (0⩽x⩽1). X-ray analysis shows that these intercalated compounds like the host 2HWSe2 also possess hexagonal symmetry with a small but continuous increase in c-parameter. However, a new phase appeared in and InWSe2 diffractograms due to In2Se3. Room temperature magnetic susceptibility, thermoelectric power experiments and two-probe conductivity measurements in the temperature range 25 −225°C indicated that intercalated compounds also exhibit n-type semiconducting behaviour similar to the host WSe2 and results are explained on the basis of existing band model. Thermal stability behaviour of these compound in atmosphere has also been studied and based on X-ray data of oxidized product formation of tungsten bronzes has been proposed.
We present the first ever experimental Compton profiles of molybdenum dichalcogenides (MoX2; X=S
and Te) using 20 Ci 137Cs Compton spectrometer. To interpret our experimental data, we have
computed the theoretical profiles, energy bands and density of states using linear combination of
atomic orbitals method in the framework of density functional theory and its hybridisation with
Hartree Fock. The energy bands and density of states using full potential linearised augmented plane
wave method have also been computed. Both theories show the existence of the indirect band gap. In
addition, the relative nature of bonding is explained in terms of equal-valence-electron-density profiles
and valence band charge densities.
A detailed investigation of crystal structure, properties and morphological characteristics of indium intercalation compound of tungsten disulphide, InxWS2 (0 1) is reported. X-ray analysis shows that intercalated compounds, like the host 2H-WS2, also possess hexagonal symmetry with a small but continuous increase inc-lattice parameter. Room-temperature thermoelectric power experiments and low-temperature (150 to 300 K) conductivity measurements indicate that intercalated compounds also exhibit p-type semiconducting behaviour similar to base material WS2. Thermal stability behaviour of these compounds in air and argon atmosphere has been studied and based on the X-ray data of oxidized products, formation of tungsten bronzes has been proposed. Results of the SEM study are also reported.
Molybdenum disulphide has been prepared by atmospheric-pressure hydrogen reduction of molybdenum trisulphide in the temperature range 400–750 C for 4 h and characterized. Chemical analysis of the product confirmed the S to Mo ratio 2.00 as desired for MoS2, consistent with its thermogravimetric analysis data in an air atmosphere. MoS2 prepared under these reducing conditions possessed a hexagonal structure with n-type diamagnetic semiconducting behaviour and a lower surface area. The catalytic activity of the MoS2 was studied for liquid-phase hydrogenation of nitrobenzene. X-ray studies on MoS3 when reduced at 750 C for 48 h indicated that MoS2 so formed is unstable, resulting in the formation of its over-reduced products Mo2S3 and Mo.
The present work deals with the synthesis, structure and properties of indium intercalated compounds of molybdenum diselenide,
In
x
MoSe2 (0≤x≤1). X-ray analysis shows that the intercalated compounds, In1/3MoSe2 like the host. 2H−MoSe2 also possess a hexagonal symmetry with a small increase inc lattice parameter. However, a new phase appeared in In2/3MoSe2 and InMoSe2 diffractogram due to In7Se6, In2Se3, In
x
Mo6Se8 or In3.33Mo15Se19. Room temperature magnetic susceptibility, thermoelectric power experiments and two probe conductivity measurements in the
temperature range 25 to 300°C indicated that intercalated compounds also exhibit p-type diamagnetic semiconducting behaviour
similar to the host MoSe2 and results are explained on the basis of existing band models. Thermal stability behaviour of these compounds has also been
studied and X-ray analysis of the oxidized product has also been made.
A detailed discussion on crystal structure of indium intercalated compounds of molybdenum disulphide, InxMoS2 (0⩽x⩽1) based on x-ray studies is reported. It shows that intercalated compounds, like the host 2HMoS2 also possess hexagonal symmetry with a small but continuous increase in c-parameter, unlike their alkali and alkaline earth metals analogs. This has been explained on the basis of the fact that there may be no increase in c-parameter at all in a given intercalation process and that this does not have purely geometric origin but also comes from electronic effects. Results of SEM study are also reported.
The transition metal dichalcogenides are about 60 in number. Two-thirds of these assume layer structures. Crystals of such materials can be cleaved down to less than 1000 Å and are then transparent in the region of direct band-to-band transitions. The transmission spectra of the family have been correlated group by group with the wide range of electrical and structural data available to yield useful working band models that are in accord with a molecular orbital approach. Several special topics have arisen; these include exciton screening, d-band formation, and the metal/insulator transition; also magnetism and superconductivity in such compounds. High pressure work seems to offer the possibility for testing the recent theory of excitonic insulators.
The present work reports on the synthesis of indium intercalation compounds InxWS2 (0 ⩽ x ⩽ 1). The material has been characterized by X-ray studies for structure determination and particle size distribution, room temperature magnetic susceptibility, thermoelectric power experiments and conductivity measurements in the temperature range 150–300 K. These results have indicated that, like the host material WS2, the intercalated compounds also possess hexagonal symmetry and are diamagnetic p-type semiconductors. The activation energy for these compounds was determined from the conductivity data.
The system AlxNbSe2 () was prepared and the phases were identified by X-ray diffraction. It was found that niobium diselenide is able to accommodate aluminum in the tetrahedral holes between the prismatic NbSe2 layers, up to the limit . In these compounds the 2s−NbS2-type structure is maintained. The AlxNbSe2 system is compared with the ternary phase CuxNbSe2 in which NbSe2 accommodates Cu in the tetrahedral holes up to , and in which on introduction of the copper atoms, the structure changes from the 2s−NbS2 type to the 2s−MoS2 type. Both and , exhibit Pauli-paramagnetic behavior.
During the investigation of complex sulfides where at least one of the elements is a transition metal, the following compounds have been prepared: Cu3NbS4, Cu3TaS4, Cu3Vse4, Cu3NbSe4 and Cu3TaSe4, all having a sulvanite structure.
Furthermore, compounds were obtained of a composition Cu10NbSa2, CuxTaS2, AgyNbS2 and AgxTaS2 in which w≈x≈y≈ 0.7 and z≈1.5.
The ionic conductivity of two dimensional alkali metal intercalation compounds depends on factors such as the ratio between the number of intercalated ions and available vacancies in the v.d.w. gap, the nature of the bonds in the host structure, the site geometry, the nature of the alcalin ion. The problems of the electrons lost by the alkali metal is discussed in light of new experimental results. A simple model assuming a delocalization in the conduction band of the host does not apply to all the systems. Two or more classes of intercalation compounds may exist.
Holes, photogenerated in d-energy bands of covalent semiconducting layer-type group VI-transition metal dichalcogenides react electrochemically differently from holes generated in semiconductors with valence bands based on p-orbitals (e. g. , CdS, ZnO, CdSe, GaAs). The chemical character of these holes as missing d-electrons, on the other hand, gives rise to very specific electrochemical surface reactions with electron donors such as I** minus , Br** minus , and even OH** minus , for example.
Layered intercalation compounds InxMCh2 (x = 0.67, 1.0) crystallize in an interesting 1T polymorph of the hexagonal structure in which the indium atoms adopt either a linear or a trigonal prismatic coordination with the chalcogens and the M atoms adopt a trigonal prismatic coordination. We measured the electrical resistivities and the Seebeck coefficients of systems of this type in the range 77–300 K. All the compounds were n type except InTaS2 which exhibited p-type metallic conductivity. No phase transitions were noted. The results are discussed in terms of charge transfer from the indium to the MCh2 layers.
Optical absorption measurements have revealed a strong shift of the fundamental absorption edge in NixZrS2 for x ≤ 0.12. The results are consistent with recent observations of a similar effect in Cu- and Fe-intercalated ZrS2 and HfS2. The charge transfer, rigid band model does not seem to be applicable for all intercalated layered transition metal dichalcogenides.
Poly crystalline molybdenum disulphide was prepared by high-pressure (56 kg/cm2) reduction of molybdenum trisulphide at 200°C. The stoichiometry was tested by chemical analysis and the crystallinity by X-ray diffraction studies. The room-temperature ac conductivity measurement showed a value of 1 × 10−4Ω−1 cm−1. The material was diamagnetic with χ⊥ = 0.05 × 10−6 emu. A band gap of 1.18 eV was obtained and n-type conductivity found. SEM studies showed 10–20 μm grain size. Temperature effect on the grain size was also studied.
The MxZrS2 systems with M = Fe, Co, Ni have been investigated: nonstoichiometric phases are observed with M in the tetrahedral sites between ZrS2 layers. Electric measurements characterize a semiconducting behaviour and suggest the occurrence of trigonal zirconium + III clusters. Magnetic measurements seem to confirm also M-M bond formation.
We report the preparation of intercalation compounds of 2H☒TaS2 with post transition period elements. In general we find that elements to the left of the metalloid line in the periodic table will intercalate TaS2. Crystallographic lattice parameters, the maximum amount intercalated per Ta, magnetic susceptibility, and superconducting transition temperatures are also given.
- Rüdorff