Non-Stoichiometric Binary Compounds

We will now extend our treatment of intrinsic defects to the non-stoichiometric non-ionized compounds, as represented by  

One example might be a halide crystal which has become non-stoichiometric due to its being heated to a temperature sufficient to cause a small amount of the halide to become volatile. 

Another case might be an oxide, heated in the presence of excess metal, 

For a non-stolchiometrlc crystal, the concentration of each point defect, in each conjugate pair, is no longer equal. If there is an excess of Vm, , or Xx, then the compound will have a surplus of X (or deficiency of M, which is the same thing) over the ideal stoichiometric composition. This is called a positive deviation firom stoichiometry. Conversely, for a negative deviation, there will be an excess of Vx, Mi, or Mm. This explains the plus and minus in equation 2.6.9. In terms of the above given defects, 6 may be expressed as shown in the following Table  

Non-Stoichiometry, 5, as a Function of Specific Types of Defects in MXs + 5 Binary Compounds 

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