Abstract

Nanohybrids containing non-stoichiometric zinc ferrite of spinel structure in an amorphous silica matrix exhibit a fundamentally different structure to that formed by stoichiometric zinc ferrite. A unique cluster glass structure, where nanocrystallites of zinc ferrite exist in amorphous Fe-rich pockets, occurred at the significantly high Fe/Zn molar ratio of 10, as supported by the magnetic behaviour and characterisation by XRD and TEM. The occurrence of zinc ferrite crystallites due to the Zn²⁺ deficiency, together with the confinement of the silica matrix, suppresses the nucleation and crystallisation of α-Fe₂O₃ to a temperature above 900 °C, preserving the cluster glass structure. The Fe/Zn molar ratio also affects the optical properties of nanohybrids consisting of the zinc ferrite nanophase in amorphous silica, which demonstrate a high absorption coefficient to yellow light. The absorption edge was blue-shifted by 0.25 eV when the Fe/Zn ratio was increased from 2 to 10.