O 2p-band

The band structure computed in Rgure 8 has 12 O 2p bands, 6 g bemds, 4 bands simpiy because the unit ceil contains two formula units, (TiC )2. There is ntn one reciprocal space varieible, but several lines (T X, X M, etc.) that refer to directions in the three-dimensional Brillouin zone. If we glance at the DOS, we see that it does resemble the expectations of 21. There are well-separated 0 2s, 0 2p, Ti g and eg bands. 

Fig. 29. Energy loss structure related to the O 2p band in CS7O (a, b) as observed with Hel (surface plasmon) and Hell radiation (volume and surface plasmon). Curve (c) shows the excitation of two surface plasmons in the Hel spectrum with a sample of approximate composition CS7O

The characteristic feature of this band structure is that the properties of the orbitals of the atoms and atomic groups are approximately preserved. The lowest band is primarily an O 2s-band. The next band is primarily an O 2p-band. These bands are fully occupied valence bands. The next band is primarily of t2 character the following band primarily of Og character. These bands are unoccupied and are called conduction bands. The Fermi level in the ideal crystal is between the highest occupied and the lowest unoccupied bands. The band gap of 3,2 eV makes Ti02 an insulator. 

Thermodynamic parameters have been calculated for NbO, and there has been an XPS study of the semiconductor-to-metal transition in Nb02/ During this transition, the Nb 4d band shifts progressively towards the O 2p band with increasing temperature until above the transition temperature the two bands merge. 

The calculation of the core levels of LajCuO discussed above was performed within the cluster approximation wherein the dependence of the spectral shape on the oxygen band-width is missed out. In order to include the effect of the oxygen 2p derived band on the spectral shape, the core-level photoemission calculation has to be performed within the impurity model which includes the O 2p band-width (instead of a single O 2p level). For reasonable values of the hybridization strength, t, the range of values of A is such that the Cu appears close to the bottom of the 

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