Origin of Structural Instability in Layered Intercalation Compounds

Abstract

The mechanisms of the phase transitions in the A_aMX₂-type intercalates (A-metal, MX₂-layered dichalcogenide matrix) occurring upon a change in the stoichiometry (a) are studied. It is shown that maximal stoichiometric ratios, and trends of structural changes in intercalates are determined by stabilization of conduction bands (“electronic stabilization”) of intercalates.     

Impurity Scattering in 3d Transition Metal Intercalation Compounds M x TiS2

Abstract

From the resistivity measurements of 3d metal intercalates M _x TiS₂ (M = Mn, Fe, Co and Ni; x = 0.05) at 4.2 K in pulsed magnetic fields up to 31 T, we have found that the residual resistivity depends on the kind of guest species. Taking into account these results and available information, we have proposed a possible band model to understand the scattering mechanism by ionized impurities of the intercalated guest M²⁺ and host Ti³⁺ ions, in satisfactory agreement with the experiments.     

Intercalation Route to Novel Superconducting Nano-Hybrids

Abstract

We have adopted novel synthetic strategies, i.e HSAB (hard-soft-acid-base) interaction and interlayer complexation concepts, to develop the superconducting nano-hybrids via intercalation technique. On the basis of these concepts, new series of inorganic-inorganic nano-hybrids, M-X-Bi₂Sr₂Ca_n-1Cu_nO_y (M = Hg, Ag, Au; X = Br, I; n = 1, 2, and 3) and of organic-inorganic ones, R₂HgI₄-Bi₂Sr₂Ca_n-1Cu_nO_y (R = organic cation) could be successfully prepared. The magnetic susceptibility measurements for these intercalates reveal that the intercalation of organic chain molecules has little influence on the superconducting transition temperature (T _c) of the pristine compounds, in spite of remarkable basal increments up to ～ 30 Å It has been also demonstrated that the present organic intercalates can be used as effective precursor materials for fabricating the superconducting thin film and nano-particle.     

Structure and Electrochemical Properties of Carbon Nanotube Intercalation Compounds

Abstract

This article summarizes the current status of carbon nanotube intercalation compounds. It focuses on the structure and electrochemical properties of intercalated single-walled carbon nanotubes (SWNTs). Materials synthesis, purification and characterization methods are also discussed. This article draws mostly from works performed at UNC.     

Neutron Magnetic Scattering of Intercalation Compounds Fex TiS2

Abstract

Neutron magnetic scattering of intercalation compounds Fe^xTiS² has been measured systematically as a function of Fe concentration x. In the x = 0.15 and 1/4 samples, so-called small-angle scattering was observed associated with a spin-glass transition. In the x = 1/2 sample, clear magnetic Bragg reflections were observed. The position of the magnetic peak with the smallest Q number was not commensurate with the nuclear lattice-unit. The magnetic structure of Fe^1/2TiS² was found not to be a simple ferromagnetic structure as was ever suggested but a long-period magnetic structure. In the x = 1/3 sample, broad magnetic diffuse peak whose Q number was also not commensurate with the nuclear lattice-unit was observed. The origin of the magnetism of Fe^1/3TiS², what is called a cluster-glass, seems the short-range ordered magnetic-clusters with a long-period magnetic structure.     

Iron-Chloranilate Intercalation Compounds: Synthesis,Crystal Structures,and Thermal Properties

Abstract

Hydrogen bond supported new iron-chloranilate assemblies, {(Hpy)[Fe(CA)₂(H₂O)₂](H₂O)}_n (py = pyridine, H₂CA = chloranilic acid, C₆H₂O₄Cl₂) (1), and [(phz)₂[Fe(CA)₂(H₂O)₂](H₂O)₂]_n (phz = phenazine, C₁₂H₈N₂) (2) have been synthesized and characterized. Compound 2 crystallizes in the monoclinic, space group C2/m (#12), with a= 29.135(6) Å, b= 16.886(6) Å, c = 15.017(5) Å, ß = 165.907(1)°, V= 1798(2) ų, Z = 2. In both the compounds two chloranilate dianions and two water molecules are coordinated to the iron ion making anionic monomers [Fe(CA)₂(H₂O)₂]^?, which are the building blocks of the compounds. The coordination environment around the iron ion in the building block is a distorted octahedron, where two water molecules sit on the trans position to each other. [Fe(CA)₂(H₂O)₂]^? anions form common layer structures, supported by hydrogen bonds. Hpy⁺ are intercalated in between the layers of 1 by electrostatic and hydrogen bonding interactions and phz are intercalated in that of 2 by electrostatic interactions. DSC traces of 1 show anomaly at 174 K, indicating phase transition in the compound.     

Structural and Magnetic Properties of FexTiSe2 Intercalation Compounds

Abstract

Magnetic and neutron studies are done about iron-intercalated titanium diselenide, Fe^xTiSe² with 0<x≤0.5. A neutron diffraction measurement shows that Fe-atoms are located between neighboring selenium layers. Magnetic measurements show that FexTiSe² are spin glasses for 0. 15≤^x≤0.22 and antiferromagnets for 0.25≤^x≤0.5. T-x magnetic phase diagram is determined. This diagram is slightly different from that determined by Huntley et al. The difference may be caused by a formation of Fe-clusters in their samples. The x-dependence of the parameters of paramagnetic susceptibilities is determined.     

Magnetic and Raman Scattering Studies on Intercalation Compounds FexNbS2

Abstract

Raman scattering spectra and magnetic susceptibility are measured in intercalation compounds Fe^xNbS² (0.159≤x≤0.325). A strong modification of Raman spectra is observed in a sample with x=0.239 (～ 0.25) which is accompanied by 2a × 2a structural change and antiferromagnetic ordering. Some correlations between magnetic ordering (antiferromagnetic or spin glass) and structural change are also discussed for wide range of Fe contents x.     

Electrical Transport Properties Of 2H-TaS2 Intercalation Compounds With Variable Charge Transfer

We report on low temperature measurements of the electrical resistivity, the Hall coefficient and the magneto-resistance in hydrated potassium intercalation compounds of 2H-TaS2, where the stoichiometry and hence the charge transfer can be varied.     

Lithium Electrochemical Intercalation into HOPG : Kinetics Analysis of One- and Two-Phases Domains

Abstract

Electrochemical intercalation of lithium ions into HOPG has been followed using the Galvanostatic Intermittent Titration Technique. The kinetics analysis presented discriminates one-and two-phases domains, taking also into account the observation of transient lithium deposition ensuing LiC₆ appearance.     

Technology of Intercalation and New Effects in PbI2 Single Crystals Intercalated by Hydrazine

Abstract

The hydrazine intercalated lead iodide single crystal technology was developed. A new type of excitons named as interlayer excitons is described. The amplification of polariton emission (Sugakov's phenomenon) and the structure phase transition under intercalation are found and studied.     

Liquid Sorption and Nanoparticle Intercalation in Layer-Structured Materials

Abstract

Alkylammonium intercalated graphite oxides (R-GO), palladium intercalated alumina-pillared montmorillonites (Pd/Al₂O₃-PILC) and titania-pillared montmorillonites (TiO₂-PILC) have been prepared and the intercalation materials have been characterized by BET surface area analysis, UV/VIS spectroscopy, ICP-AES, DTG-DTA, XRD and TEM measurements. R-GO particles were prepared by oxidation of natural graphite followed by organophilization with cationic surfactants. For TiO₂-PILC and Pd/Al₂O₃-PILC the synthesis included the interlamellar adsorption of precursor species (polyaluminium-hydroxide, Pd-acetate and tetraethyl orthotitanate) from dilute solutions and subsequent chemical reactions at the montmorillonite/solution interface.     

Structural Phase Transition of an Intercalation Compound Mn1/4NbS2

Abstract

A structural phase transition of an intercalation compound Mn_1/4NbS₂ has been investigated by X-ray diffraction at high temperatures. The lattice parameter c exhibited a discontinuous change at 640K. The superlattice reflections observed below 640K disappeared suddenly above 640K. The phase transition at 640K took an aspect of the first-order phase transition. The precise structure analyses were performed at various temperatures above and below the phase-transition temperature. It was revealed that Mn atoms were arranged in disorder in the high-temperature phase, while the Mn atoms were ordered forming the 2a ₀ × 2a ₀ × c ₀ superlattice in the low-temperature phase. The Nb and S atoms around the ordered Mn atoms slightly shifted from the high-symmetry position in the low-temperature phase. The order parameters were the degree of order of the Mn atoms and the degree of displacement of the Nb and S atoms.     

Hydrogen Intercalation in Potassium-C60

Abstract

Solid state ¹H NMR of (KH)₃C₆₀ was measured in the temperature range between ?80 and 60 °C. A doublet spectrum composed of main peak at ?7.0 ppm and shoulder peak at ～0 ppm was observed at room temperature. The negative chemical shift of the main peak indicates that hydrogen in (KH)₃C₆₀ exists as a hydride-like ion. The 60 °C spectrum became singlet at ?5.8 ppm due to motional narrowing.     

Potassium Doped Single Wall Carbon Nanotubes: Resistance under Pressure

Abstract

We report in situ measurements of four-probe de resistance (R) of K-doped purified single wall carbon nanotube (SWNT) “buckypaper” as a function of quasi-hydrostatic pressure. Doped samples show completely different behavior compared to that of pristine nanotubes in the pressure range up to 90 kbar. The characteristic increase in the resistance of pristine buckypaper above 10 kbar, associated with the formation of kinks or/and twists of tubes, is not observed in K-doped samples. This may originate from 1) a substantial change in electronic band structure of donor intercalated nanotubes, 2) completely different transport properties of defect structures, or 3) higher stiffness of doped SWNT's which prevents formation of kinks and twists in this pressure range. On deintercalation, the pristine behavior of R(P) is restored, establishing the reversibility of potassium vapor-transport doping.     

Electrical and Optical Properties of Conducting Polymer and Carbons in Nano-Scale Periodic Structure and their Intercalation Effects

Abstract

Nano-scale periodic structures of conducting polymer and carbons, which were prepared by infiltration of polymers and carbons in nano-scale interconnected periodic pores in synthetic opals made of regular array of SiO₂ spheres and then removing SiO₂ by etching, have been found to exhibit novel electrical and optical properties. Their electrical and optical properties in thus fabricated conducting polymer and carbon replicas change drastically upon pyrolysis due to progress of carbonization and graphitization. That is, due to the changes in periodicity, pore size, carbonization degree and crystal structure, electrical conductivity, magnetoconductance and their temperature dependences and optical reflection spectra have changed drastically. These replicas with porous nature can be infiltrated and also intercalated with various materials, resulting in also remarkable changes of properties. The synthetic opal infiltrated with conducting polymer can be electrochemically doped, with which remarkable change of optical properties have been observed due to the shift of the diffraction peak accompanying with the change in refractive index. Alkali metal intercalated carbon and graphite with nano-scale periodic structures have been also studied. The applications of these nano-scale periodic structures of conducting polymer and carbon are also discussed.     

EXAFS and XANES Studies on 3d Transition Metal Intercalation Compounds M x TiS2

Abstract

EXAFS and XANES spectra of Ti K-edge have been measured for 3d transition metal intercalation compounds M _x TiS₂ (M = Mn, Fe, Co and Ni; x ≤ 0.33). We have found that the interatomic distance between Ti and the first nearest neighbor S atoms, R(Ti-S), increases with the guest concentration x. The variation in XANES spectra with x reveals the reduction of the valence state of Ti atoms upon intercalation of M. From these results as well as the M K-edge EXAFS data studied previously, we have proposed a simple model on the local structure of M _x TiS₂ to reproduce the observed values of R(Ti-S) by averaging local shift of S atoms caused by intercalation.     

Novel mixed–solvothermal synthesis of MoS2 nanosheets with controllable morphologies

MoS₂ nanosheets with controllable morphologies were successfully synthesized via a novel mixed–solvothermal approach based on interfusing organic solvent in the solution. The morphology of the MoS₂ nanosheets was lamellar–like using the mixed water/ethanol/N–Methyl pyrrolidone solvents, whereas that prepared with the mixed water/ethano/ethylene glycol solvents changes to fullerene–like. Because of the structure‐directing ability of organic molecules, the mixed solvents were proposed to be responsible for the formation of such different morphologies. The average size of MoS₂ nanosheets was approximately 90 nm, and the thickness was about 10–20 nm. The results indicated that the crystalline phase and morphology were largely influenced by calcination and reaction system.     

Structural Studies of Antimony Pentahalide Graphite Intercalation Compounds Using 001 Reflections

X-ray diffraction studies at room temperature are reported of stages 1, 2 and 3 SbCl_mF_5-m graphite intercalation compounds (m = 0, 2, 4, 5). The analysis of the 001 reflection inten-sities shows the periodic stacking of carbon, chlorine and antimony layers in all compounds. The results are in good agreement with the structural model recently found in other metal halide graphites. But we have found that the antimony atoms are not located on the mirror plane (z = O) in the centre of the intercalate layer. In case of dilute SbCl₅ graphites, the identity period along c axis I_c increases with SbCl₅ concentration in the stage 2 com-pound. Interlayer distances were determined in dependence on SbCl₅ concentration. A molecular layer form consisting of SbX₅ molecules which are linked by halogen bridges is suggested to fill the galleries in the graphite lattice.     

插层法制备g-C3N4/高岭石复合材料及其光学性能

高岭石表面与层间具有较高的活性和良好的规范性,因而适合对其进行化学修饰,在催化剂负载方面值得深入研究.本文以甲氧基嫁接的高岭石为前躯体,采用置换插层法制备出高岭石/三聚氰胺插层复合物,进一步在550 ℃煅烧获得g-C3N4/高岭石复合光催化剂.利用X射线衍射、傅里叶红外和热重-差热分析等手段对复合光催化材料进行表征,并对其光催化性能进行研究.结果表明,当高岭石与光催化剂前驱体三聚氰胺质量比为1∶1和1∶2时,较难缩聚得到g-C3N4;然而,当高岭石与三聚氰胺质量比为1∶3、1∶4、1∶5时,可获得不同g-C3N4占比的复合材料,其整体分散状况因高岭石的加入而有效改善,这表明高岭石的加入能有效避免g-C3N4的团聚.所制备的高岭石负载石墨相氮化碳光催化材料具有较好的光学性能,在探索经济、高效、绿色矿物基复合光催化剂方面研究具有重要意义.