Free parameter of spinel structure and M$\stackrel{..}{o}$ssbauer lineshift

The dependence of the M$\stackrel{..}{o}$ssbauer lineshift $\delta$ in oxygen ferrite - spinels on the free parameter of the structure u is considered. It is shown that the mutual disposition of the lines for the A and B points in the spectrum depends significantly on the oxygen parameter u. Within the framework of the field theory of ligands, theoretical dependences are obtained for the difference in the shifts $\Delta\delta^{ВА} = \delta^B — \delta^A$ as a function of u, at various values of the lattice parameter a. This difference is expedient for comparison with experimental data, since it does not depend on the choice of radiation source and scarcely depends on a. The available experimental data for ferrite - spinels with $Fe^{3+}$ ions at points A and B are found to be in agreement with the results of the calculations. In particular, the trend of the difference $\Delta\delta^{BA}$ to sign reversal with rise in u is confirmed. According to the results of the calculations, sign reversal should be observed at $u= u_{кр} = 0.3845$ for the case when $a=8.30 \stackrel{o}{A}$.