Alkaline earth oxide study

Souda R, Yamamoto K, Hayami W, Aizawa T, Ishizawa Y (1994) Bond ionicity of alkaline earth oxides studied by low-energy D+ scattering. Phys Rev B Condens Matter 50 4733-4738 Spasojevicde-Bire A, Kiat JM (1997) Electron deformation density smdies of perovskite compoimds. Ferroelectrics 199 143-158... 

Turning to non-metallic catalysts, photoluminescence studies of alkaline-earth oxides in dre near-ultra-violet region show excitation of electrons corresponding to duee types of surface sites for the oxide ions which dominate the surface sUmcture. These sites can be described as having different cation co-ordination, which is normally six in the bulk, depending on the surface location. Ions on a flat surface have a co-ordination number of 5 (denoted 5c), those on the edges 4 (4c), and dre kiirk sites have co-ordination number 3 (3c). The latter can be expected to have higher chemical reactivity than 4c and 5c sites, as was postulated for dre evaporation mechanism. 

Extensive study has been devoted to paramagnetic defects that are formed on high-surface area alkaline earth oxides, particularly magnesium oxide. The work carried out by Wertz el al. 187, 188) and Henderson and Wertz 139) on bulk defects formed in MgO single crystals has been quite valuable in the identification of the surface defects. Both the bulk and surface defects may be divided into two classes those in which an electron... 

Alkaline earth oxides (AEO = MgO, CaO, and SrO) doped with 5 mol% Nd203 have been synthesised either by evaporation of nitrate solutions and decomposition, or by sol-gel method. The samples have been characterised by chemical analysis, specific surface area measurement, XRD, CO2-TPD, and FTIR spectroscopy. Their catalytic properties in propane oxidative dehydrogenation have been studied. According to detailed XRD analyses, solid solution formation took place, leading to structural defects which were agglomerated or dispersed, their relative amounts depending on the preparation procedure and on the alkaline-earth ion size match with Nd3+. Relationships between catalyst synthesis conditions, lattice defects, basicity of the solids and catalytic performance are discussed. 

Surface basicity can also be examined by indicator dyes, but there has beef much less study of surface basicity than of surface acidity. Phenolphthalein, bromothymol blue and various nitro-analines have been used to assess the effect of dehydration on the basicity of alkaline earth oxides or hydroxides, using benzoic... 

Our work has applied these techniques to the study of the binary insulating materials including the fluorites, alkali halides, alkaline earth oxides, and perovskites. Many of these are simple materials that are commonly used as models for all solid state defect equilibria. Our work has had the goal of determining at the microscopic level the defect equilibria and dynamics that are important in understanding solid state chemistry as well as developing new tools for the studies of solid materials. 

Strontium. Strontium like Rb and Pd was included in anticipation of a standard. Strontium may be subject to more ionization and chemical interferences than other alkaline earths. Thorough studies of interfernces from mineral acids, HC1, HNO, and l SO are reported (3) as well as from Al, Si, and other ionization enhancement elements. Sr is strongly ionized, 84%, in nitrous oxide/acetylene the addition of 1000 ppm Cs is very important in suppressing Al, Si, and other interferences that cause enhancement. The 460.7 nm line is significant for AAS analysis of Sr. 

A parallel approach has been to study the photo luminescent spectra of the alkaline-earth oxides (148-150). The absorption of light corresponds to the... 

Small quantity of crystalline material of cnbic stractnre for study [e.g., alkali hahdes, alkaline earth oxides, cnprons or silver halides, simple metals such as aluminum or copper (finely powdered with a file)] liqnid (medinm boiling petroleum ether) for density woik. 

Stone F.S., Garrone E., Zecchina A. Surface properties of alkaline earth oxides as studied by UV-visible diffuse reflectance spectroscopy. Mater. Chem. Phys. 1985 13 331-46. 

The inclusion of impurity atoms in MgO is much more interesting from a chemical point of view when alkali metals are used to replace Mg ions. In fact, this results in trapped-hole centers. The MVO pairs have been extensively studied in the bulk of alkaline-earth oxides by optical studies, EPR and ENDOR measurements [185,186] as well as by embedded cluster calculations [187]. The LiVO ions create an effective dipole which polarizes the surrounding lattice, with the two ions moving toward each other. The presence of an O radical, however, is most interesting when one is dealing with surface properties. This center in fact is very reactive and is the subject of the next paragraph. 

Electronic levels (T ) and vibrational-rotational constants of the observed states are from the optical study of Barrow et al. (J ) and the microwave work of Tiemann et al. (2). Other low-lying electronic states and their vibrational-rotational constants are estimated in isoconfIgurational groups by analogy with BaO (8) and from trends observed in the known states of the other alkaline-earth oxides and sulfides. Thermodynamic functions are calculated using first-order anharmonlc corrections to and in the partition function Q = exp(-c ej /T). Uncertainty in the energy and molecular constants for the... 

The bulk crystal form of the alkaline earth oxides is the NaCl structure. The bulk termination at the (100) surface consists of a stack of coplanar bilayers each containing one cation and an anion. CaO(lOO) has been the subject of a LEED study which found a contraction of top interlayer spacing by —1.2% (Prutton et al., 1979). Buckling of the top bilayer was not investigated. Buckling of the top bilayer was found in a recent LEED study of MgO(lOO) (Blanchard et al. 1990). In this case, the oxygen atom moves out of the surface by 0.05 0.025 A whilst the Mg atom sinks into the surface the same distance. The center-of-mass plane of the top MgO bilayer is unrelaxed. The (100) surface of transition metal oxide CoO, which also has... 

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