Case studies of non-stoichiometric compounds

As can be verified, Ep equals Therefore it has been shown that eqn (1.133) is identical to eqn (1.135). From this, the creation and annihilation of electrons and holes in semiconductors may be written as the following chemical equation 

The equation can also be considered as the ionization of a valence bond, 

lattice defects such as point defects and carriers (electrons and holes) in semiconductors and insulators can be treated as chemical species, and the mass action law can be applied to the concentration equilibrium among these species. Without detailed calculations based on statistical thermodynamics, the mass action law gives us an important result about the equilibrium concentration of lattice defects, electrons, and holes (see Section 1.4.5). 

So far we have discussed the basic concept of non-stoichiometry without showing real examples. Here we shall consider case studies in order to understand the non-stoichiometry appearing in various kinds of substances. To construct phase diagrams which contain non-stoichiometric compounds, it is indispensable to know the relationship between the deviation from stoichiometry 5, the partial pressure of coexisted gas, (for diatomic gases), 

In principle the deviation 5 can be determined by the use of usual analytical chemistry or a highly sensitive thermo-balance. These methods, however, are not suitable for very small deviations. In these cases the following methods are often applied to detect the deviation physico-chemical methods (ionic conductivity, diffusion constant, etc.), electro-chemical methods (coulometric titration, etc.), and physical methods (electric conductivity, nuclear magnetic resonance, electron spin resonance, Mossbauer effect, etc.), some of which will be described in detail. 

---

CASE STUDIES OF NON-STOICHIOMETRIC COMPOUNDS 83 concentration 8 in a mole fraction of Cu2- O is written as... 

---