Hole-mixing states

Figure 3. (a)The temperature dependence of TEP is reproduced with our mixed state model, (b) Hole doping dependence of one of fitting parameters T with the characteristic temperatures, Th, Tt and Tc (See the text.). Fitting parameters, y and p are also shown with variation of doping concentration in the inset. 

Secondly, photoelectron spectroscopy gives the distribution of all mixed states and the spectrum is disturbed by the photoionization probabilities of the various symmetries as a consequence, it is sometimes difficult to interpret the results. On the other hand, the X-ray spectra involve the distributions of known symmetries, i.e. those states from which the transitions toward the inner hole are possible considering the transition probabilities. 

The relative populations of the Xe2+ 4d 2 levels produced in this process are governed by the symmetry of the mixing state. Once formed, the double hole states decay by a double Auger process, again involving a cascade through Xe3+ intermediate states, to final states of Xe4+. 

This particle-hole excitation is illustrated in Fig. 3.4. Now, for translationally invariant Hamiltonians iF is a good quantum number. However, unlike the noninteracting Hamiltonian, the interacting Hamiltonian mixes states with different k. ... 

Correlation, or many-body effects, can be classified according to the many-body factor Xx- If Xx is close to 1, the MO picture, the aufbau principle, a Koopmans theorem and the quasi-particle picture hold. The analysis of the Auger spectrum can then be conducted solely in terms of MO theory. When more than one Xx enters in the wavefunction, we have hole-mixing effects and electronic interference in the transition cross sections, in analogy to the case of photoelectron spectra. When only one Xx is large, but this Xx is present in more than one state, one can then not associate a one-to-one correspondence between MOs (or MO factors in Eq. 3.39) and spectral bands (states). The states in question are thus associated with a breakdown of the MO picture. It could, finally, also be that no Xx is large, in which case we talk about a correlation-state satellite. 

Solid mixed ionic-electronic conductors (MIECs) exhibit both ionic and electronic (electron-hole) conductivity. Naturally, in any material there are in principle nonzero electronic and ionic conductivities (a i, a,). It is customary to limit the use of the term MIEC to those materials in which a, and 0, 1 do not differ by more than two orders of magnitude. It is also customary to use the term MIEC if a, and Ogi are not too low (o, a i 10 S/cm). Obviously, there are no strict rules. There are processes where the minority carriers play an important role despite the fact that 0,70 1 exceeds those limits and a, aj,i< 10 S/cm. In MIECs, ion transport normally occurs via interstitial sites or by hopping into a vacant site or a more complex combination based on interstitial and vacant sites, and electronic (electron/hole) conductivity occurs via delocalized states in the conduction/valence band or via localized states by a thermally assisted hopping mechanism. With respect to their properties, MIECs have found wide applications in solid oxide fuel cells, batteries, smart windows, selective membranes, sensors, catalysis, and so on. 

As a result of strong electronic interactions between the two metalloporphyrin units, there is a substantial uncertainty in assigning oxidation states in mixed-valence group 2 complexes of redox-active metals, such as Co. Thus, although reduced neutral C02 derivatives can be reasonably well described as those of Co the location (metal versus porphyrin) of the electron hole(s) in the singly and doubly oxidized derivatives is not known definitively, and may be very sensitive to the medium [LeMest et al., 1996, 1997]. For example, in benzonitrile, the UV-vis spectmm of [(FTF4)Co2]" ... 

In chemisorbed systems, the molecular orbitals of the adsorbate are mixed with the electronic states of the substrate, producing strong adsorption bonds, i.e. the frequency of the adsorbate mode is well above the highest phonon frequency of the substrate. The relaxation of these vibrational excited states via emission of substrate phonons has only a low probability, because many phonons have to be enoitted during the decay. Non-radiative damping by electron-hole pair excitation appears to be the dominant relaxation path in these systems. 

The diffusivity is independent of the motion of any other species (e.g. electrons or holes) and is not influenced by internal electrical fields as in the case of chemical diffusion processes which require the simultaneous motion of electronic or other ionic species. The partial ionic conductivity of the mixed ionic and (predominantly) electronic conducting electrode is given by the product of the concentration and the diffusivity and may be related to the variations of the steady state and transient voltage ... 

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