Lanthanum band structure

B3N6] A [BN3] and N (Fig. 8.11). Band-structure calculations performed for La3(B3N5) revealed a band gap in the order of 4 eV. The corresponding nitridoborate oxide La5(BN3)Og [30] is also salt-Hke, owing the typical nitridoborate structure pattern regarding the environment of the [BN3] ion with lanthanum... 

Fig. 8.12 Crystal structure (a), band structure of La3(B2N4) (b), and orbital interactions along [B2N4] stacks (c) (interactions with lanthanum orbitals are omitted for clarity).

Based on the results of our band-structure calculations we assume that the metal-like properties of lanthanum nitridoborates are related by B-B interactions between adjacent BNx units in structures. 

Perovskites, 27 358 band structure, 38 131-132 crystal structure, 38 123-125 Perovskite-type oxides see also specific lanthanum-based catalysts actinide storage in radioactive waste, 36 315-316... 

The trivalent rare-earth crystal structure sequence from hep - Sm type -> La type -> fee, which is observed for both decreasing atomic number and increasing pressure, is also determined by the d-band occupancy. Figure 8.11(a) shows the self-consistent LDA energy bands of fee lanthanum as a function of the normalized atomic volume fi/Q0, where Q0 is the equilibrium atomic volume. We see that the bottom of the NFE sp band moves up rapidly in energy in the vicinity of the equilibrium atomic volume as the free electrons are compressed into the ion core region from where they are repelled by orthogonality constraints (cf eqn (7.29)). At the same time the d band widens, so that the number of d electrons increases under pressure... 

The 3d levels in lanthanides are far removed from 4f levels and the overlap of these two levels if any is very small. As a result, multiplet structure in the 3d region is not expected. Although this is the case, XPS of some lanthanide compounds, particularly elements from lanthanum to neodymium, exhibit splitting in the bands apart from the doublet due to spin-orbit interaction. This type of structure is shown in Figs. 9.10, 9.11 and 9.12. These splittings are known as satellites and originate from multielectronic excitations. In general,... 

Wan et al. (170) carried out an IR spectroscopic study of the adsorption of S02 on partially substituted lanthanum and cobalt perovskites. The spectrum of Lao.6Sro.4Coi, Mjc03 after poisoning with S02 at 200°C included bands at 1133 and 994 cm-1 that are assigned to a bridging structure of adsorbed S02 (species I) ... 

Perovskite structures of rare earth titanate oxides are of considerable interest in recent years [63,64], Among different rare earth metals, lanthanum was the most investigated. In order to accommodate the excess oxygen, the replacement of divalent cations such as Ca or Sr in general perovskite materials by a tri-valent cation such as La " resulted in excess electrons and slabs of a distorted perovskite structure. With the highly donor-doped (110) perovskite, the separation of electrons and holes is more facile than other semiconductor materials because of a narrower depletion layer and a more drastic band bending. In this way the activity of the photocatalytic processes were improved. As obviously, to suppress the recombination of the generated electrons and holes is an important condition [63,64]. 

Lanthanum monochloride LaCl has been less studied. Xin and Klynning (1994) reported molecular constants obtained from analysis of the rotational structure of IR bands in the thermal emission spectrum of LaCl recorded on a high-resolution Fourier transform spectrophotometer. It is worth noting that, despite a rather strong emission spectrum of LaCl, Xin and Klynning (1994) failed to detect the absorption spectrum of this compound. In this context, these authors selected, with low confidence and, apparently by analogy with the conclusions of Schall et al. (1983), the... 

Lithium can be inserted into the material up to at least 0.08 Li" " per formula unit. This level of intercalation is insufficient for the number of lithium and lanthanum cations to exceed unity and so the A sites of the perovskite structure still contain some vacancies at this stoichiometry. Whilst this intercalation process is reversible, experiments using this electrolyte in conjunction with a graphite electrode show that an irreversible oxidation process occurs. The reduction of Ti" " narrows the band gap and leads to electronic conductivity of 0.01 S cm at room temperature. This reactivity and electronic conduction would lead to a rapid discharge via short circuit of a stored battery and so makes these materials unsuitable for use as an lithium electrolyte in these applications. 

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