Mössbauer spectroscopy of Zn_xMg_1-x Fe₂O₄ (0 ≤ x ≤ 0.74) nanostructures crystallized from borate glasses

Glasses in the system 51.7 B₂O₃/9.3 K₂O/1 P₂O₅/10.4 Fe₂O₃/(27.6 − y) MgO/y ZnO (with y = 0, 1, 2.5, 5, 7.5, 10, 13.8, and 20) were prepared by the conventional melt quenching method. The glass samples were thermally treated at 560 °C for 3 h in ambient conditions. Using ⁵⁷Fe Mössbauer spectroscopy, the effect of the substitution of MgO by ZnO in the glass network and the effect on the precipitated crystallized phase was studied. The results showed that the ratio of Zn²⁺:Mg²⁺ in the precipitated crystals increases with the ZnO concentration in the glass. The isomer shift values indicated that iron occurs as Fe³⁺, which is distributed at the tetrahedral (A) and the octahedral [B] sites. Introducing ZnO leads to a relative increase of the Fe³⁺ concentration at the B sites at the expense of that occupying the A sites. This indicates the precipitation of Zn_xMg_1-x Fe₂O₄ nanoparticles, where Zn²⁺ ions favorably occupy the A sites. The average hyperfine field of the samples showed a strong dependence on the Zn concentration. At the highest Zn concentration of 13.8 and 20 mol%, the samples are paramagnetic, while for the smaller ones, the samples are superparamagnetic.