Cerium band structure

Nd2-xCexCu04, 112,427-45 band structure schematic, 717 cerium oxidation state, 431 comparison with La2CuO>4 systems, 320 composition range, 437 copper oxidation state, 427,442 crystal chemistry, 428-31 crystal growth, 244,436-7,442-4... 

Villain, J., l959, J. Phys. Chem. Solids 11, 303. Waber, J.T. and A.C. Switendick, 1965, Results of augmented plane wave calculation of the band structure of cerium metal. Proceedings of the Fifth Rare Earth Research Conference, Ames, Iowa, 1%5, Book II. pp. 75-88. 

Relativity affects the kinetic term and the exchange-correlation potential in the Kohn-Sham equation. As investigated in detail for the uranium atom and the cerium atom, the relativistic effect on the exchange correlation potential is rather small and therefore we use /Ac[ ( )] in n relativistic band structure calculation. The relativistic effect on the kinetic term is appreciably large and can be taken into account by adopting the Kohn-Sham-Dirac one-electron equation instead of eq. (3) as follows ... 

We start with the question of what happens to the large orbital moment of f electrons when they are hybridized with other states in solids. This question, of course, is central to understanding the unusual properties of actinide (and cerium) compounds. Form-factor measurements had shown the importance of hybridization effects in compounds such as UGej (Lander et al. 1980), but at that time no theory had been developed to handle these effects in particular the orbital contribution was known to be incorrectly treated in band-structure calculations (Brooks et al. 1984, Brooks 1985). Brooks, Johansson, and their collaborators corrected this deficiency by adding an orbital polarization term in the density-functional approximation (see the chapter by Brooks and Johansson (ch. 112) in this volume). When they made calculations on a series of intermetallic compounds, particularly those with a transition metal in the compact fee Laves phase, they found that the value of was reduced compared to the free-ion values. Loosely speaking, we can associate such a partial quenching of the /j ,-value with the fact that the 5f electrons have become partially itinerant, and we know that fully itinerant electrons (in the 3d metals, for example) have 0. 

Fig. 26.11. Proposed electronic band structure for cerium hydride (Libowitz et al., 1972).

Optical Absorption Spectra and Electronic Structure The optical spectra of all the doubledeckers are listed in Table I, On first glance, Ce(0EP)2 has a "normal" spectrum (7), However, the spectrum shows extra bands and therefore should be called "hyper", A small band appears at 467 nm (maybe a ligand-to-metal charge transfer band), and broad features extend far into the near infrared (NIR), The latter absorption may be due to exciton interactions. Contrary to the known rare earth monoporphyrins (7), it has been shown for the closely related cerium(IV)... 

Another transient aminoxyl radical has been generated , and employed in H-abstraction reactivity determinations" . Precursor 1-hydroxybenzotriazole (HBT, Table 2) has been oxidized by cyclic voltammetry (CV) to the corresponding >N—O species, dubbed BTNO (Scheme 9). A redox potential comparable to that of the HPI —PINO oxidation, i.e. E° 1.08 V/NHE, has been obtained in 0.01 M sodium acetate buffered solution at pH 4.7, containing 4% MeCN". Oxidation of HBT by either Pb(OAc)4 in AcOH, or cerium(IV) ammonium nitrate (CAN E° 1.35 V/NHE) in MeCN, has been monitored by spectrophotometry , providing a broad UV-Vis absorption band with A-max at 474 nm and e = 1840 M cm. As in the case of PINO from HPI, the absorption spectrum of aminoxyl radical BTNO is not stable, but decays faster (half-life of 110 s at [HBT] = 0.5 mM) than that of PINO . An EPR spectrum consistent with the structure of BTNO was obtained from equimolar amounts of CAN and HBT in MeCN solution . Finally, laser flash photolysis (LFP) of an Ar-saturated MeCN solution of dicumyl peroxide and HBT at 355 nm gave rise to a species whose absorption spectrum, recorded 1.4 ms after the laser pulse, had the same absorption maximum (ca 474 nm) of the spectrum recorded by conventional spectrophotometry (Scheme 9)59- 54... 

Also shown in the Table are the relative positions, Q, in energy of the different band centres (when hybridization is neglected) and the Wigner-Seitz radii in an assumed fee structure. From Eq. (5) and Table 1 one estimates for iron, nickel, uranium, cerium, gadolinium and americium... 

Application of Raman spectroscopy to a study of catalyst surfaces is increasing. Until recently, this technique had been limited to observing distortions in adsorbed organic molecules by the appearance of forbidden Raman bands and giant Raman effects of silver surfaces with chemisorbed species. However, the development of laser Raman instrumentation and modern computerization techniques for control and data reduction have expanded these applications to studies of acid sites and oxide structures. For example The oxidation-reduction cycle occurring in bismuth molybdate catalysts for oxidation of ammonia and propylene to acrylonitrile has been studied in situ by this technique. And new and valuable information on the interaction of oxides, such as tungsten oxide and cerium oxide, with the surface of an alumina support, has been obtained. 

This is the case with fluoro complexes and the crystal structure of (NH CeFd shows the coordination is nearly square antiprismatic with cerium having eight fold coordination [140], However the compounds Cs2NaMF6 and analogous chloride have octahedral coordination [139]. Raman spectra of the chloro compounds of La, Pr, Nd and Er have been obtained [146-148]. Raman spectra along with the far infrared spectra of Nd and Er show the octahedral coordination of the lanthanide ion. For these complexes the location of Aig band is as follows La = 274 cm-1 Pr = 281 cm-1 Nd = 278 cm-1 Er = 289 cm"1. 

The applications of ceria based materials are related to a potential redox chemistry involving Cerium(III) and Cerium(lV), high affinity of the element for oxygen and sulfur, and absorption / excitation energy bands associated with its electronic structure. Important areas for application of cerium based materials are catalysis and chemicals, glass and ceramics, phosphors and metallurgy. 

We prepared by sol-gel some thermally stable Zro.io(Cei-xPrx)o.9o02 mixed oxides (x between 0 and 0.75) with a fluorite-type structure. This structure was confirmed by the presence, in the Raman spectrum, of a single band ca. 460 cm characteristic of the M-0 vibration in the fluorite-type structure. Moreover, the band position and the shoulder at 570 cm indicate the presence of oxygen vacancies probably associated with praseodymium cations. Consequently, high OSCs appears to be the result of the presence of both cerium and praseodymium atoms. Thus, addition of praseodymium atoms into zirconia-ceria oxides appears to be very promising for the design of new automotive catalysts. 

DRS measurements support the TPR results. The impregnated catalysts and steam treated (IMPV) did not show the presence of V after the reduction. Probably, the hydrogen consumption in the TPR profile is due to the reduction of cerium. The band in the d-d transition can be attributed to the formation of alloys like cerium vanadate, according to the literature [14]. Baugis et al. [15] reported that the presence of vanadate with rare earth decreases the diffusion of vanadium in the zeolite structure [14]. The existence of these compounds may affect the oxidation state, the dispersion, morphology and location of cerium species in the catalyst. 

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