Fermi level ionic levels

I. Riess, and C.G. Vayenas, Fermi level and potential distribution in solid electrolyte cells with and without ion spillover, Solid State Ionics, in press (2001). 

Fig. 4-21. Electron energy levels of an ionic electrode of silver-silver chloride in ion transfer equilibrium cfia ) = Fermi level of electron in silver part of electrode snvAfCici-) = equivalent Fermi level to transfer equilibriiun of silver ions and chloride ions in silver-silver chloride electrode.

Fig. 9-16. Polarization curves of anodic oxidative dissolution and cathodic reductive dissolution of semiconductor electrodes of an ionic compound MX iiixcp) (iMxh )== anodic oxidative (cathodic reductive) dissolution current solid curve = band edge level pinning at the electrode interface, dashed curve = Fermi level pinning.

Fig. 6. Schematic partial density of states scheme for an NaCl-type (binary) compound (with UN as an example) with f electrons delocalized and unhybridized. Uranium is on the left and nitrogen on the right. In ascending order nitrogen valence band f-band tied to the Fermi level the d conduction band. The Fermi level is at zero on the energy scale. The unhybridized band centres, Qi, are shown on the right. This unhybridized model corresponds to the fully ionic model...

As has been pointed out previously, ionic compounds are characterized by a Fermi level EF that is located within an s-p-state energy gap Ef. It is for this reason that ionic compounds are usually insulators. However, if the ionic compound contains transition element cations, electrical conductivity can take place via the d electrons. Two situations have been distinguished the case where Ru > Rc(n,d) and that where Rlt < Rc(n,d). Compounds corresponding to the first alternative have been discussed in Chapter III, Section I, where it was pointed out that the presence of similar atoms on similar lattice sites, but in different valence states, leads to low or intermediate mobility semiconduction via a hopping of d electrons over a lattice-polarization barrier from cations of lower valence to cations of higher valence. In this section it is shown how compounds that illustrate the second alternative, Rtt < 72c(n,d), may lead to intermediate mobility, metallic conduction and to martensitic semiconductor metallic phase transitions. 

Electronic structure calculations for transition metal carbides (Neckel 1990, Le 1990, Le et al. 1991) reveal significant contributions to cohesion by all three main types of chemical bonding. Covalent bonds are due to the formation of molecular orbitals by combining atomic d-orbitals of the metal with p-orbitals of C. Ionic bonds result from charge transfer from the metal to the non-metal. Metallic bonds are due to s electrons and also to a non-vanishing density of d-p electronic states (DOS) existing at the Fermi level (Figure 7.30). The main difference between the DOS curves calculated for stoichiometric ZrC, TiC or HfC and NbC, TaC or VC is... 

Figure 2. Electronic and ionic disorder in ionic solids and in water in physical" (top) and chemical language (bottom).20 The coupling of the ionic and electronic Fermi levels takes place via the chemical potential of the neutral components (here + + Jt = //Ag ) (see Fig. 3). A further relevant example could be the breaking-up of an ion...

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