Barium , crystal structure

Table 21-IV shows some properties of the metals and their crystal forms. Since different crystal forms are involved in the series, trends in the properties are obscured. Figure 21-2 shows scale representations of the crystal structures of metallic beryllium, calcium, and barium.

The difference in catalytic activity between the La- and the Ba-based hexa-aluminates results from the following reasons the first difference is the valence of cation in the mirror pleuie between tri-valent lanthanum ion and di-valent barium ion. The second is the crystal structure between magnetoplumbite and P-alumina, which are different in the coordination of ions and concentration of Frenkel-type defect in mirror plane. The redox cycle of transition metal in hexa-aluminate lattice, which closely related with catalytic activity, is affected sensitively with these two factors. 

As discussed in more detail in Section 2.02.4.2.2.(iii), almost all the metallocenes of calcium, strontium, or barium are bent, even when unsolvated. The only exception to this so far is the sterically crowded (CsPr Ba 152 (Figure 79),348 whose X-ray crystal structure reveals a linear geometry with Ba-C = 2.997(4)A. All three... 

Studies of the metal-exchange process of P.R.49 (Na) to P.R.49 1 (Ba) [1] revealed that the process, apart from the temperature, is not only influenced by the crystal structure and the concentration of the barium ions but also by the amount of rosin soap. Colophony-based rosin which is assumed to act as a surfactant, is converted during the laking process into colorless insoluble rosinate salts. These salts are incorporated in the pigment til up to 30% by weight without a loss of tinctorial strength. Very often the color strength is even increased, accompanied by a color shift to more bluish reds. 

Fig. 35 The crystal structure of the 1 1 intramolecular sandwich complex barium...

Newnham R. E. and Megaw H. D. (1960). The crystal structure of celsian (barium feldspar). Acta Cryst., 13 303-312. 

Barium chlorate, Ba(C103)2, is a colorless solid with a monocUnic crystal structure. It decomposes thermally above its melting-point temperature of 687 K according to ... 

Donohue, P. C., L. Katz, and R. Ward The crystal structure of barium ruthenium oxide and related compounds. Inorg. Chem. 4, 306 (1965). 

Yttrium-barium-copper oxide compounds YBa2Cu306+x (x = 0.6-1), generally abbreviated to 123, with a Tc of 90K which is above the temperature of liquid nitrogen, are of great importance (2). As noted earlier, Tc is governed principally by the crystal structure... 

The crystal structure of the 1-2-3 superconductor, YBazCusOy- is depicted in Figure 10.8. Figure 10.8(a) depicts only the positions of the metal atoms. If we discuss it in terms of the perovskite structure ABO3, where B=Cu, the central section is now an A-type perovskite unit cell and above and below it are also A-type perovskite unit cells with their bottom and top layers missing. This gives copper atoms at the unit cell corners and on the unit cell edges at fractional coordinates A and Ys. The atom at the body-centre of the cell (i.e., in the centre of the middle section) is yttrium. The atoms in the centres of the top and bottom cubes are barium... 

The crystal structure of a barium picrate complex of (139) reveals a 2 2 dimeric structure of the form [(139)Ba(picrate)3Ba(139)]+(picrate) (148), 47 which is unique as three picrate anions are held in the space between the ligated cations. The cations are not sited within the macrocyclic cavities but are displaced towards the centre of the dimer. This situation is reminiscent of the Cs+-polyether dimer structure (Figure 15d). The outer surface of the (139)Ba(picrate)2 complex is highly lipophilic, and the bulky phenyl residues provide screening for the enclosed anions. 

A breakthrough in superconductor technology came with the discovery24 of yttrium barium copper oxide, YBa2Cu307, whose crystal structure is shown here. When heated, the material readily loses oxygen atoms from the Cu-O chains, and any composition between YBa2Cu307 and YBa2Cu3Ob is observable. 

Similar structural principles are evident in compounds obtained by the metallation of l,2-bis(dimethylamino)-l,2-di-9-fluorenyldiborane (LH2) by MN(SiMe3)2 (M = Na or K) or by cesium metal in hexane-THF (lithium, calcium, and barium derivatives have also been made).93 The dianions were characterized by NMR spectroscopy, and the crystal structures of K2L.4THF, 53, and K2L.2DME, 54, were determined (Fig. 33). In each the... 

The dielectric constant of barium titanate, along [001] is about 200 and along [100] it is 4000 at room temperature.3 The spontaneous polarization at room temperature is 26 X 10-6 C./cm.2, and the value of the coercive field has been found to vary from 500 to 2000 volts/cm. The crystal structure of barium titanate at room temperature can be represented by a tetragonal unit cell with size of a0 = 3.992 A., and c0 = 4.036 A., but the symmetry becomes cubic above 120°C., at which temperature the crystals no longer exhibit ferroelectric properties. 

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