Samarium compounds pressure

Intercalation compounds involving layered double-hydroxides (LDHs), illustrated by the structure shown in Figure 19 (Park et al., 2002), were synthesized to facilitate the measurement of the uniaxial stress (i.e., along the direction perpendicular to the layers), that host layers exert on intercalated species. Below a certain thickness of -A 00 mm, the intercalated structures become more transparent to visible light, so that the information obtained by PL represents the properties of the bulk, not of the surface. Because it is sensitive to the deformation of the intercalants, the PL from samarium complexes was employed to measure the uniaxial stress, by using PL peak positions as a function of pressure (Park et al., 2002 Sapelkin et al., 2000). 

Figures 20A and B show the PL spectra, recorded at 290 K, at 600 nm, and as a function of pressure, for Cs9(SmW10O36) and SmWi0O36-LDH, respectively (Park et al., 2002). For the sake of comparison, the line shapes are normalized and displaced along the vertical axis. In both cases, the peak position is red-shifted by 4—5 nm when the hydrostatic pressure increases from 1 bar to 61 kbar. It was shown that the red-shift from A to A lies solely in the deformation of the samarium complexes by the uniaxial stress exerted by the host layers, whereas the shift from B to B is also influenced by the change in the cation environment. Under the same conditions, B is not at the same position for the non-intercalated (HN (n -b u t y 1) 3) 9 (SmW10O3e) and Cs9(SmWi0O36) compounds (Park et al., 2002). Thus only peak A is available to measure the unixial stress. This observation can be used to determine the uniaxial stress, when the external pressure is zero. For the SmW10O36—LDH system, the uniaxial stress varies significantly from 75 at 28 K to 140 kbar at 290 K (Park et al., 2002).

Also the pressure-dependent wavelength of the fluorescence maximum of a samarium-doped borate has been calibrated. The compound has the advantage of allowing for more precise determinations at very high pressures (above approximately 100 GPa) and it was demonstrated that, in contrast to ruby, the line position exhibits only a negligible temperature dependence. ... 

For a higher conductivity, cerium dioxide can be doped either with gadolinium Cei cGd (02 or with samarium Cex jSmj02 doped cerias are quite stable chemicdly. In solid oxide fuel cells they lack the effect of interactions between the electrolyte and the cathode materials that would lead to the formation of poorly conducting compounds. However, doped cerias have an important defect in that at low oxygen partial pressures (such as those existing close to the anode) they develop a marked electronic conduction. This is entirely inadmissible for the electrolyte, as it leads to internal self-discharge currents and even to a complete internal short circuit. The electronic conduction comes about when Ce" ions in the lattice are partly reduced to Ce " ions, which creates the possibility for electrons to hop between ions of different valency. 

The nature of 4f electrons in lanthanides and their compounds, either localized or itinerant, is responsible for most of their physical and chemical properties. Localized states corresponding to tightly bound electron shells or to narrow bands of correlated electrons near the Fermi level are observed for all lanthanides. Pressure has a striking effect on the electronic structure, which, in turn, induces structural changes. For instance, crystal structure transitions from hexagonal closed packed (hep) samarium type double... 

Leger etal. (1980,1981) have described the preparation, at high pressures, of the metallic monoxides for the elements from lanthanum to samarium and have determined their structure and conductivities. A negative PAV term in the free-energy expression makes it possible to synthesize the monoxides from a mixture of the metal and the sesquioxide under pressure. These monoxides can be maintained at normal pressures after,preparation. The monoxides through NdO are metallic, golden-yellow compounds with the Ln atom being trivalent. SmO is metallic with a valence close to... 

Squire found that improved conversions of aromatic compounds and higher yields of aromatic amine were obtained when the aromatic compound reacted with ammonia in the presence of water at elevated temperamre and pressure using a conditioned Ni/NiO/Zr02 cataloreactant [67]. Delpesco also provided a strategy for improving the conversions of aromatic compounds to aromatic amines by prolonging the life of cataloreactant at a temperamre from about 150-500 °C at a pressure of from about 10-1000 atm. To this end, a dopant such as an oxide of lanthanum, samarium, holmium, europium, erbium, praseodymium, neodymium, terbium, ytterbium, dysprosium, yttrium, or mixtures thereof was added into Ni/NiO/Zr02 cataloreactant [68]. 

Ytterbium dicyclopendienide was prepared by reducing dicyclopentadienyl ytterbium chloride with finely dispersed sodium metal in tetrahydrofurane (Calderazzo et al., 1966). Samarium(II) dicyclopentadienide was isolated as the 1-tetra-hydrofuranate. This compound was prepared by reaction between SmfCsHj), and potassium naphthalene in tetrahydrofurane (Watt et al., 1969). It is insoluble in this solvent and very air-sensitive. Desolvation of the compound at elevated temperature under reduced pressure is accompanied by decomposition. 

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