Preparation of ZnFe2O4/SiO2 and CdFe2O4/SiO2 nanocomposites by sol–gel method

The purpose of this paper is to characterise the phase relations in the system ZnFe2O4/SiO2 and CdFe2O4/SiO2 by dependence on the thermal treatment. Both ferrites have the structure of normal spinels. The samples were prepared by the sol–gel method, heated at a temperature of 800–1100 °C and characterised by high-resolution transmission electron microscopy (HRTEM), X-ray diffraction, and Mössbauer spectroscopy. HRTEM revealed nanocrystals of the size of about 5–10 nm, depending on the heat treatment temperature. The spinel structure of ZnFe2O4 in the amorphous silica matrix proved to be very stable up to 1100 °C without decomposition to the zinc silicate and iron (III) oxide. On the other hand, CdFe2O4 already starts to decompose at 900 °C and complete decomposition to the α-Fe2O3 and cadmium silicate can be observed at 1100 °C. This decomposition is also accompanied with the recrystallisation of the silica matrix to quartz and cristobalite.