Characterization of hydrothermally synthesized ZnFe2O4 spinel ferrite: Insights into microstructure, inversion degree, and crystal evolution

Spinel-type compounds are known for their substantial chemical and structural variability, which arises from the unique cation distribution characterized by a range of partial to total cell inversion degrees. In this study, we first assessed the preparation of ZnFe2O4 particles synthesized using a hydrothermal method and subsequent calcination. The synthesized particles were characterized using scanning electron microscopy (SEM), Raman spectroscopy, X-ray diffraction, Rietveld refinements, and Williamson-Hall fittings to evaluate the microstructural features. The degree of inversion of the crystalline systems was quantified using the Bertaut method. The effect of post-synthesis heat treatments on the crystal evolution of the synthesized particles was investigated at different temperatures (400, 600, and 800 °C) and durations (1, 4, and 8 h). The compressive crystal evolution of the particles with various degrees of cell inversion was observed and correlated with the different heat treatment conditions. The evaluated degrees of inversion were 0.59 (inversion), 0.34 (random), and 0.26 (standard). The cation distribution suggests that the spinel structure can be inverted at the nanoscale regime. The proposed method of particle preparation allows for tuning both the cation distribution and the crystal evolution of the particles from inverted to standard.