Layered compounds alkali

Fig. 2. A nonclassical view of staging proposed by Herold and co-workers (JI3). From left to right are first-, second-, and third-stage compounds. (—, Carbon layer oooo, alkali-metal layer.)...

Tributsch H (1982) Photoelectrochemical Energy Conversion Involving Transition Metal d-States and Intercalation of Layer Compounds. 49 127-175 Truter MR (1973) Structures of Organic Complexes with Alkali Metal Ions. 16 71-111 Tytko KH, Mehmke J, Kurad D (1999) Bond Length-Bond Valence Relationships, With Particular Reference to Polyoxometalate Chemistry. 93 1-64 Tytko KH (1999) A Bond Model for Polyoxometalate Ions Composed of M06 Octahedra (MOk Polyhedra with k > 4). 93 65-124... 

The layered compounds AMO2 where M is a transition metal and A an alkali metal, Cu or Ag have attracted interest because of their electrical properties. LiCo02 is used in rechargeable lithium ion batteries and Na, Co02 is metallic except at x = 0.5 and for values of x of about 0.35 becomes superconducting in the presence of intercalated water. Li et and Xu and Zeng have studied Nao.5Co02. A... 

The crystal structure of these compounds was first determined by Schleede and Wellmann 79). In the compound CgMe a layer of alkali metal atoms is present between each pair of carbon planes, whereas in the blue alkali-poor compound this occurs between every other pair. Introduction of the alkali metal increases the interplanar distance to 5.41 A for potassium, 5.61 A for rubidium, and 5.95 A for cesium. According to the definition given in the introduction these two compounds are referred to as the first and second stage. 

The calculations also perhaps explain the difference in composition between the small, Earth-like inner terrestrial planets and the large outer Jovian planets. The terrestrial planets presumably condensed at much higher temperatures and are thus composed of metals, metal oxides, and silicates. The Jovian planets would have formed at far lower temperatures within the primitive solar nebula and consist predominantly of frozen volatile compounds such as methane, water, ammonia, and so on. Finally, a possible case for early layering of the Elarth can be drawn from the calculations within a cooling nebula metallic Fe and Ni would condense first, followed by spinels, pyroxenes and olivines, with a final lower temperature layer of alkali feldspar, metal oxides, hydrated silicates and, of course, water itself at 0°C. 

Intercalation compounds Alkali metals react with graphite in such a way that they get between the layers of graphite and cause the layers to expand. Intercalation compounds are commonly composed of the alkali metals, bromine, or some electron donor molecules such as amines or organometallic compounds. This is found in lithium ion batteries, for example. 

Photoemissive devices can be conveniently divided into two historical (and performance) classes depending upon the material used as the photoemissive layer [5.11]. The first class is the classical group [5.26]. Here the photoemitter is a thin evaporated-layer compound containing an alkali metal or metals (almost always including Cs), one or more other metallic elements from group VB of the periodic table (e.g., Sb), and possibly also oxygen and/or silver [5.27], For ultraviolet applications several other sensor materials are used (e.g., Csl), but such devices become highly specialized and are not discussed further in this chapter [5.28]. 

Although there are numerous families of lamellar solids, only a handful of them exhibit the kind of versatile intercalation chemistry that forms the basis of this book. In arriving at the content of this volume, the editors have accurately identified six classes of versatile layered compounds that are at the forefront of materials intercalation chemistry, namely, smectite clays, zirconium phosphates and phos-phonates, layered double hydroxides (known informally as hydrotalcites or anionic clays ), layered manganese oxides, layered metal chalcogenides, and lamellar alkali silicates and silicic acids. Graphite and carbon nanotubes have not been included, in part because this specialty area of intercalation chemistry is limited to one or two molecular layers of comparatively small guest species that are capable of undergoing electron transfCT reactions with the host structure. 

Graphite reacts with alkali metals, for example potassium, to form compounds which are non-stoichiometric but which all have limiting compositions (for example K C) in these, the alkaU metal atoms are intercalated between the layers of carbon atoms. In the preparation of fluorine by electrolysis of a molten fluoride with graphite electrodes the solid compound (CF) polycarbon fluoride is formed, with fluorine on each carbon atom, causing puckering of the rings. 

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