Composite prismatic structur

Composite prismatic structure the c-axis of rhombic prisms align parallel to the shell. The rhombic prism is an aggregation of aragonite needle crystals aligned in conical form in its elongation direction. 

In the meantime, homoatomic ligand-free Zintl clusters of tetrel atoms are known for compositions [ 4 , [ 5] , and [ g] with = Si, Ge, Sn, Pb and n = 2-4. A unique example of a cluster with ten vertices is [Pbio] with a bicapped quadratic anti-prismatic structure (Figure 3.1). The smallest clusters [ 4]" were first prepared in solid-state reactions of alkali metals (A = Na, K, Rb, Cs) with elemental tetrels ( = Si, Ge, Sn, Pb) in a 1 1 ratio [8]. 

The crystal structures of the phases in these systems are characterized by destabilization of the octahedral structure elements and the appearance of trigonal prismatic structural elements. F.c.c. monocarbides MeCj v in the Mo-C and W-C system exist only at high temperatures and with substoichiometric compositions. The stoichiometric monocarbides WC and MoC are hexagonal. 

A plethora of stoichiometries and structural types are found for the chalcogen compounds of the Group 5 metals. Phases approximating to the composition MX have the NiAs-type structure, whereas the MX2 compounds have layer structures related to M0S2, Cdl2, or CdCl2 types. Sometimes complex layer sequences occur in which the 6-coordinate metal atom is alternatively octahedral and trigonal prismatic. 

Different ways of the structural classification of deposits exist. In one system, the following structures are distinguished arbitrarily (1) fine-crystalline deposits lacking orientation, (2) coarse-crystalline deposits poorly oriented, (3) compact textured deposits oriented in field direction (prismatic deposits), and (4) isolated crystals with a predominant orientation in the field direction (friable deposits, dendrites). The structure of metal deposits depends on a large number of factors solution composition, the impurities present in the solntion, the current density, surface pretreatment, and so on. 

It should be noted here, that not only the (chemical and morphological) composition of the protective layers at the basal plane surfaces and prismatic surfaces is different, but that these layers also have completely different functions. At the prismatic surfaces, lithium ion transport into/ffom the graphite structure takes place by intercalation/de-intercalation. Here the formed protective layers of electrolyte decomposition products have to act as SEI, i.e., as transport medium for lithium cations. Those protective layers, which have been formed on/at the basal plane surfaces, where no lithium ion transport into/from the graphite structure takes place, have no SEI function. However, these non-SEI layers still protect these anode sites from further reduction reactions with the electrolyte. 

According to Rogl (1992) the triangular prismatic coordination M6B is the predominant structural building block in an intermediate composition range (between a B/M atomic ratio included between 1/8 and 4/1). Less frequent are the M6B octahedral and the M8B square anti-prismatic coordinations. 

As might be anticipated for minerals with chain structures, pyroxenes commonly occur in columnar, prismatic, rodlike, and acicular forms. Enstatite has been found in the form of rosettes of fine-fibrous crystals. Special names such as victorite, chladnite, and shepardite were assigned to different occurrences in this distinctive morphology, possibly because the fibrous aggregates were located in iron meteorites. However, the composition and crystal... 

Despite their monocrystalline habit, the nacreous tablets and the prismatic units of Mollusks shells are composite structures. We do note that these complex structures are rarely visible on simple fractures of the shells, but enzymatic hydrolyzes or/and acidic etchings are effective from this point of view. 

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