Effect of La3+ on thermal, structural and morphological properties of Zn–Co ferrite spinel-based pigments

The paper discusses the structural, morphological, and chromatic characteristics of La3+ substituted Fe3+ in Zn–Co–La ferrite embedded in a SiO2 matrix, synthesized through a sol-gel method. The thermal behavior of reactants during the synthesis process revealed the formation of metallic oxalate up to 200 °C and their decomposition into metal oxides that further react and form ferrites. The rate constants of oxalate decomposition into ferrites calculated using the isotherms at 160, 200, 240, and 280 °C decrease with increasing temperature and depend on the Fe3+ substitution with La3+ in Zn–Co–La ferrite. The XRD patterns showed a nano-crystalline, single-phase structure formation. The lattice constant increased from 8.431 Å to 8.466 Å, and the crystallite size registered a growth from 35 to 64 nm with the increase in La3+ cations. FT-IR spectra revealed the existence of the M − O stretching bands from Zn–Co–La ferrite and the formation of SiO2 matrix. Transmission electron microscopy revealed spherically-shaped ferrite particles with a particle size of 38–67 nm. The particle size increases with increasing the La content. The lightness of pigments is low and increases by embedding in opaque ceramic glazes. Synthesized NCs were tested for their potential application as pigments in the ceramic industry through their incorporation into glazes. This evaluation included assessing their color using CIELAB coordinates.