On the deviation from the Vegard's law for the solid solutions

A method is proposed for calculating the lattice parameter (l) for the solid solution (i.e. disordered binary substitutional alloy), which takes into account the pressure (P) in the alloy. An analytical expression is obtained for calculating the dependence of the function l on the alloy concentration at different values of P. It is shown that for P = 0 the deviation from the Vegard's law (Delta l) is due to the difference in compressibility and in specific volumes of the pure crystals. The method is approved on SiGe, CuAu and AuFe alloys, and it was showed the good agreement with the experimental data. With an isothermal increase in pressure, the value.l increases both for alloys with a negative and for alloys with a positive deviation from the dependence obtained by the Vegard's law. Calculations showed that for the SiGe alloy, the function Delta l(P) passes over to the positive region at P-0 = 0.685 GPa. It was shown the thermal expansion coefficient of a solid SiGe substitution solution at P = 0 deviates in the negative direction from the dependence that follows from the Vegard's law.