This approximation is well suited to mixed crystals at small concentrations of one component or at very high temperature where the interactions between the A and B components can be neglected. Larger concentrations of both components usually lead to additional ordering, and in some respects these alloys can be likened to the order in a liquid where Brillouin zones have no conventional meaning. Derivation of the compositional dependence of E g under these conditions requires special theoretical analysis and calculations. In particular G is expressed as if A-B alloy is an ideal solution. The value of W can be expressed as an interaction energy between pairs of different atoms.
V b are the molar volumes.
Moreover it would be expected that the atomic structure of the nitrides has no serious distortions during cooling from the growth temperature. These reasonable assumptions allow us to link S xx with the actual crystal growth temperature. Figure 1 schematically demonstrates the thermodynamic diagram for a regular solution. Alloys grown at temperatures and compositions in the range under the spinodal are spatially inhomogeneous. The nitride T c values are shown in table 1 .