Mössbauer spectroscopy of Zn x Mg 1-x Fe 2 O 4 (0 ≤ x ≤ 0.74) nanostructures crystallized from borate glasses

Glasses in the system 51.7 B 2 O 3 /9.3 K 2 O/1 P 2 O 5 /10.4 Fe 2 O 3 /(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 57 Fe 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 Zn 2+ :Mg 2+ in the precipitated crystals increases with the ZnO concentration in the glass. The isomer shift values indicated that iron occurs as Fe 3+ , which is distributed at the tetrahedral (A) and the octahedral [B] sites. Introducing ZnO leads to a relative increase of the Fe 3+ concentration at the B sites at the expense of that occupying the A sites. This indicates the precipitation of Zn x Mg 1-x Fe 2 O 4 nanoparticles, where Zn 2+ 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.