Intercalated ions

K+ is generally used as the reversibly intercalating ion since it leads to insoluble compounds for all the forms. In the mixed-valence Prussian Blue compound, Fe is in the high-spin state and coordinated octahedrally with the N ends of the cyaiudes, whereas Fe is low-spin and octahedrally coordinated with the C ends of the... 

Fig. 7.1 Sites for intercalated ions between close-packed layers of anions (a) octahedral and tetrahedral sites (b) trigonal prismatic sites.

These hosts consist of chains weakly bonded to one another. One example is a series of compounds of Mo and Se, in which cubes of Mo and Se are arranged in chains, and can accommodate guest ions between the chains (Chevrel and Sergent, 1982). In these compounds, it is possible to remove the intercalated ions and separate the chains in solution (Tarascon et al., 1985). 

Organic polymers are widely used in modified electrodes [220], but inorganic materials such as zeoHtes, clays or microporous solids are attractive as replacements since they have much better stability, tolerance to high temperatures and oxidizing conditions, and chemical inertness. Due to the capability of clays to exchange intercalated ions, clay modified electrodes have been extensively studied. 

The minerals of the pyrophyllite [(Al2Si40io(OH)2)]-ferripyrophyllite [(Fe 2Si40io(OH)2)] series are related to the mica group. The structure of these minerals closely approximates that of muscovite with the two tetrahedral sheets and octahedrally coordinated intercalated ions, a 2 1 layering (Fig. 2.13) but there is little substitution of Si " by Al Only two-thirds... 

Nickel or cupric hexacyanoferrate film electrodes have been also used for amperometric detection of intercalating ions in a flow-injection system (K+ and NH4+ in urine and K+ in blood samples)... 

The underlying motivation of the work presented in this paper is to provide a theoretical understanding of basic physical and chemical properties and processes of relevance in photoelectrochemical devices based on nanostructured transition metal oxides. In this context, fundamental problems concerning the binding of adsorbed molecules to complex surfaces, electron transfer between adsorbate and solid, effects of intercalated ions and defects on electronic and geometric structure, etc., must be addressed, as well as methodological aspects, such as efficiency and reliability of different computational schemes, cluster models versus periodic ones, etc.. 

Such seggregation of the bound guest molecules is an important aspect in these systems. Photoluminescence spectra of intercalated Ru(bpy) + showed a broad, partly structured emission. The luminescence maximum was at 591 nm for the direct intercalated ions (Fig. 57a) and around 597 nm for the guest ions intercalated via preintercalation of alkylammonium ions (Fig. 57b). In all the cases, the... 

In custom-designing materials with tailored properties, it is often necessary to s)m-thesize metastable phases that will be kinetically stable under the temperature and conditions of use. These phases are obtainable only through kinetic (chemical) control. In many cases, kinetic control has been achieved via the soft chemical low-temperature (e.g. electrochemical synthesis, sol-gel method) and/or topochemical routes (e.g. intercalation, ion exchange, dehydration reactions), since these routes use nuld synthetic conditions. It should be noted that not all soft chemical routes are topochemical. A reaction is said to be under topochemical control only if it follows the pathway of minimum atomic or molecular movement (Elizabe et al., 1997). Accordingly, topochemical reactions are those in which the lattice of the solid product shows one or a small number of... 

Figure 7.28). If we consider as spheres, this leads to the normal four spheres, eight tetrahedral holes and four octahedral holes per unit cell of a face-centred cubic lattice. The two holes have significant size differences, and as a result has extensive intercalation chemistry. For example, caesium is too large to be accommodated in the tetrahedral holes but fits comfortably into the octahedral holes. Once has been reduced it is known as a fulleride. The intercalated ions are mostly either metals of Group 1 or 2, where the former is most common. 

Although the basic structure is the same, the intercalated ions cause the molecule orientation to become fixed and non-rotating, with a six-membered ring pointing towards each cation. The effect of the intermolecular separation of the on is striking and is illustrated... 

In order to explore the thermodynamic properties, and especially the chemical potential ofthe intercalation compounds, a lattice gas model [10] has been adopted under the assumption that intercalated ions are localized at specific sites in the host lattice, with no more than one ion on any site, and that local and global electroneutrality is observed and there is no strong interaction between the electrons and the intercalated ions. It should be noted that, in solid-state chemistry, this model is often referred to as ideal solution approximation when used to describe the thermodynamics of nonstoichiometric compounds. According to this model, the chemical potential of A in A8MO2 in Equation (5.3) can be divided into two terms as... 

The chemical potential - that is, the change in the Gibbs free energy G with the number of the intercalated ions (n) - can be divided into two parts related to the enthalpy (fi) and entropy (S) variations ... 

The simplest way to approach the intercalation thermodynamics based on the lattice gas model is to assume that the intercalated ions do not interact with one another, that the available sites are equivalent and occupied by the ions at random, and that the chemical potential of electrons are constant. The entropy of distributing ions randomly on a fraction 8 of the available sites (N) in the intercalation compounds is... 

For most insertion compounds, the interaction of intercalated ions with each other in the host lattice is not negligible. In order to simply consider the contribution of ionic interaction in Equation (5.8), it is often assumed that each ion experiences a mean interaction or energy field from its neighboring ions, based on a mean-field theory [10]. According to this approximation, the contribution to the chemical potential is proportional to the fraction of sites occupied by the ions 5, and hence the interaction term is introduced into Equation (5.8) as... 

In these systems the anode provides the intercalating ions. It is an efficient and mild method in which the intercalation reaction can be controlled through the current passed. The reaction occurs spontaneously in a chemical concentration gradient. 

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