Cation distribution and quadrupole interaction in tin-substituted zinc ferrites

Mossbauer and X-ray diffraction studies of the tin-substituted zinc ferrites Zn_1+xSn_xFe_2-2xO₄ have been carried out and the cation distribution Zn(Zn_xSn_xFe_2-2x)O₄ has been established using both the methods. ⁵⁷Fe Mossbauer spectra in these spinel solid solutions with x=0.0 to 0.9 are reported at 77K and 295K. The ¹¹⁹Sn Mossbauer spectra have been used to identify the site occupancy of tin and show its presence at octahedral sites only. ⁵⁷Fe Mossbauer spectra show well resolved quadrupole doublets for all the compositions studied. A monotonic increase in the value of quadrupole splitting with increasing tin content is observed. This is attributed to the change in the oxygen parameter of the spinel structure with addition of tin. No detectable change in the value of quadrupole splitting is observed with the change in temperature, which suggests that the quadrupole splitting is mainly of lattice origin. The value of the isomer shift does not change with tin concentration, which indicates that the s-electron charge distribution of Fe³⁺ ions is not influenced by tin substitution. An increase in the value of the isomer shift with decreasing temperature is attributed to the second-order Doppler shift.