Mixed host lattices

Non-stoichiometry and Mixed Host Lattices in Inorganic Clathrates... 

During electrochemical reduction (charge) of the carbon host, lithium cations from the electrolyte penetrate into the carbon and form a lithiated carbon Li rCn. The corresponding negative charges are accepted by the carbon host lattice. As for any other electrochemical insertion process, the prerequisite for the formation of lithiated carbons is a host material that exhibits mixed (electronic and ionic) conductance. 

Isomorphism. TiC is isomorphous with TiN and TiO. Thus oxygen and nitrogen as impurities, or as deliberate addition, can substitute for carbon to form binary and ternary solid solutions over a wide range of homogeneity. These solutions may be considered as Ti(C,N,0) mixed crystals. TiC forms solid solutions with the other monocarbides of Group IV and V. It is the host lattice for WC.li" ... 

The main drawbacks of solid-state techniques are that (i) the distribution of the dopant in the host lattice may not be even since the precursors are not mixed on the atomic scale, and (ii) particle growth cannot be easily controlled and so milling and sieving is necessary. 

The luminescence of Bi " is quite diverse and depends strongly on the host lattice (Boulon 1987 Blasse and Grabmaier 1994 Blasse et al 1994). For the heavy Bi " the transitions between the ground state and the Pi state becomes additionally allowed by spin-orbit mixing of the Pi and Pi states. After excitation at low temperature, the system relaxes to the lowest excited state. Consequently, the emission at low temperatures can be ascribed to the forbidden transition Pq- Sq and has a long decay time. Nevertheless, both Pi and Po are emitting levels and they are very close so that at higher temperatures the luminescence from the Pi level may appear with a similar spectrum, but shorter decay (Fig. 5.49). 

Colored mixed-metal oxide pigments result from the incorporation of color-giving transition metal ions into an oxide host-lattice (see Table 5.9-13). Depending upon the particle size and properties of the chosen host, pigments (0.2 to 2 pm) or ceramic colorants (stains) (up to ca. 10 pm) result, which in many cases are characterized by high thermal and chemical stability and thus are suitable for the coloring of enamels and ceramics. 

The second result is not always obtained, but depends strongly on the specific connection pattern of the polyhedra in the host lattice structure and on the pattern of the cation distribution as well. For example no shift of the ligand-field bands is observed within the mixed crystal series Znj, Cu,jSb206 with increasing x (Table 1),... 

Scheme 8. Enantioselective Photoreactions in TADDOL Inclusion Compounds with a Cou-marin, a Methacryl Anilide, and an Oxocyclohexenyl-carboxamide. In the first case, the packing of the coumarin molecules in the mixed crystal is such that the double bonds are predisposed for the (2+2) cycloaddition. In the second example, a photochemical electrocychc reaction is followed by a sigmatropic H shift. The third reaction is an intramolecular (2+2) cycloaddition with dia- and enantioselective formation of three new stereogenic centers. There are several more reactions of this type, described in the literature [54], and the Toda group has determined the crystal structures of a number of inclusion compounds to show the correlation between the crystal packing and the configuration of the photoproducts. EMastereoselective solid-phase reactions of chiral guests in TADDOL-host lattices have also been described by the...

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