Alkali-Metal Intercalates

Doping of alkali-metals into CNTs has been examined [11]. The X-ray powder diffraction (XRD) patterns of the K- or Rb-doped CNTs show that alkali-metals are intercalated between the CNT layers. The hexagonal unit cell is essentially the same as that of the stage-1 alkali-metal intercalated graphite ACg (A=K, Rb). For a sample doped with Rb, the observed lattice parameter of the perpendicular... 

As future outlook, it would be of great relevance to be able to eventually enhanee the intrinsic conductivity of CNTs. In this respect, the latest development in alkali metal intercalated CNTs looks rather promising. In faet, Chauvet et al. recently sueeeeded to dope aligned CNT by potassium and found that the Pauli susceptibility increases a factor of 3 upon doping, indicating that K-doped tubes are still good eonductors [23]. 

Metal chalcogenides, apart from their technological significance in industrial applications, have played an important role in the development of new synthetic concepts and methods in the area of solid-state chemistry. A great example is alkali metal intercalation into TiS2 (Chap. 6) first reported three decades ago, which highlighted the then-novel synthetic approach called soft chemistry chimie douce). This low-temperature process allows for new compounds to be obtained while retaining the structural framework of the precursor. Related to this concept is the... 

In alkali metal intercalation compounds, the guest is ionised in the host, donating its outer s electron to the host s electronic energy levels. Thus there are two aspects to consider, the sites where the ion resides, and the energy levels or bands that the electron occupies. Guests such as water that remain neutral will only be discussed in the section on cointercalation. In some hosts, notably graphite, some guests accept electrons from the... 

IV layered transition metal dichalcogenide-alkali metal intercalation compounds. The advantage of this method is that it is carried out at room temperature and, consequently, there is less likelihood of reaction between sodium and the reaction vessel. On the other hand, this method is more difficult in that it involves the use of liquid NH3. Furthermore, undesirable side reactions may occur if the NH3 is not dried thoroughly or if the reaction vessel is not clean. For example,... 

Intercalation of cations into a framework of titanium dioxide is a process of wide interest. This is due to the electrochromic properties associated with the process (a clear blue coloration results from the intercalation) and to the system s charge storage capabilities (facilitated by the reversibility of the process) and thus the potential application in rocking-chair batteries. We have studied alkali-metal intercalation and ion diffusion in the Ti02 anatase and spinel crystals by theoretical methods ranging from condensed-phase ab initio to semiempirical computations [65, 66]. Structure relaxation, electron-density distribution, electron transfer, diffusion paths and activation energies of the ion intercalation process were modeled. 

Many samples are unstable in air. Examples of air-sensitive compounds are alkali metal intercalated C60, carbon nanotubes, and graphite, which are... 

Additional electrons can be transferred to the C82 molecules via alkali-metal intercalation under standard intercalation conditions, for both systems saturation is reached at six K ions per endohedral fullerene molecule. 

When TDAE (a liquid at room temperature) is added to C60 in solution, the resulting salt crystallizes as small particles, which can be removed by filtration. TDAE+Cg0 is a charge-transfer salt with a monoclinic structure, different from the high-symmetry cubic structures of pristine C60 and its alkali metal-intercalated derivatives [83]. 

Since the discovery of high temperature superconductivity in cuprates, there has been intense interest in transition metal oxides with strongly layered, (quasi) two-dimensional (2D) crystal structures and electronic properties. For several years now alkali-metal intercalated layered cobaltates, particularly Na CoCL (NxCO)withx 0.50 — 0.75, have been pursued for their thermoelectric properties [1] IAX C0O2 is of course of great interest and importance due to its battery applications. The recent discovery[2] and confirmation[3-5] of superconductivity in this system, for x 0.3 when intercalated with H20, has heightened interest in the NxCO system. 

Alkali metal intercalation involving a redox reaction is readily carried out electrochemically by using the host (MCh2 dichalcogenide) as the cathode, the alkali metal as the anode and the non-aqueous solution of the alkali metal salt as the electrolyte ... 

Alkali metal intercalation in dichalcogenides is also achieved by direct reaction of the elements at around 1070 K e.g. AxMCh2 whereM=V, Nb or Ta) in sealed tubes. Alkali metal intercalation compounds with dichalcogenides form hydrated phases, A HjOJy MCh2, just like some of the layered oxides e.g. 

This situation, clear in the case of more ionic structures, is less stringent in graphite intercalates where, presumably, there is electron transfer to (in the case of alkali-metal intercalates) or from (in the case of metal halide intercalates) the half-filled conduction bands of the graphite layers (produced by overlap of the 7t orbitals). Similarly, the periodicity requirements are less stringent for the alternating composite layers of layer silicates with complex intralayer and interlayer charge balance. 

Table 3 Graphite-alkali metal intercalation compounds...

A variety of chemical reagents may also be used to form alkali metal intercalation compounds. The first compounds of the dichalcogenides were prepared by RiidorfF, who reacted the host lattices with liquid ammonia solutions of the alkali... 

Figure 19 Compositions of the alkali metal intercalation com-poimds of TiS2 and ZrS2. (Reprinted with permission from Ref. 4, by permission of Oxford University Press). The numerals refer to the stage, and a, b to different layer stackings (see text)...

Alkali metal intercalation reactions have been intensively studied for systems involving lithium. Host oxides are those of elements in high oxidation states that possess lower valence states that are also stable in oxides. Lithium intercalation may be carried out by Lil solutions for easily reducible systems, for example. 

Woollam, J.A., Flood, D.J., Wagoner, D.E., Somoano, R. and Rembaum, A., Magnetic Field Effects on Superconductivity in Alkali Metal Intercalates of M0S2, NASA TM-X-68109, (1972). 

The catalytic properties of the intercalates depends on the material asso-cated with the graphite. Alkali-metal intercalates favour base-catalysed reactions of hydrocarbons and these were reviewed by Pines and Schaap in 1960. In all cases, the catalytic activity of the graphite intercalate is different from that expected on the basis of the components alone. 

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