Screening of Mono-, Di- and Trivalent Cationic Dopants for the Enhancement of Thermal Behavior, Kinetics, Structural, Morphological, Surface and Magnetic Properties of CoFe2O4-SiO2 Nanocomposites.

CoFe2O4 is a promising functional material for various applications. The impact of doping with different cations (Ag+, Na+, Ca2+, Cd2+, and La3+) on the structural, thermal, kinetics, morphological, surface, and magnetic properties of CoFe2O4 nanoparticles synthesized via the sol-gel method and calcined at 400, 700 and 1000 °C is investigated. The thermal behavior of reactants during the synthesis process reveals the formation of metallic succinates up to 200 °C and their decomposition into metal oxides that further react and form the ferrites. The rate constant of succinates' decomposition into ferrites calculated using the isotherms at 150, 200, 250, and 300 °C decrease with increasing temperature and depend on the doping cation. By calcination at low temperatures, single-phase ferrites with low crystallinity were observed, while at 1000 °C, the well-crystallized ferrites were accompanied by crystalline phases of the silica matrix (cristobalite and quartz). The atomic force microscopy images reveal spherical ferrite particles covered by an amorphous phase, the particle size, powder surface area, and coating thickness contingent on the doping ion and calcination temperature. The structural parameters estimated via X-ray diffraction (crystallite size, relative crystallinity, lattice parameter, unit cell volume, hopping length, density) and the magnetic parameters (saturation magnetization, remanent magnetization, magnetic moment per formula unit, coercivity, and anisotropy constant) depend on the doping ion and calcination temperature.

The Effect of Ni2+ Ions Substitution on Structural, Morphological, and Optical Properties in CoCr2O4 Matrix as Pigments in Ceramic Glazes.

The structural, morphological, and optical properties of Ni2+ ions substitution in CoCr2O4 matrix as ceramic pigments were investigated. The thermal decomposition of the dried gel was performed aiming to understand the mass changes during annealing. The X-ray diffraction (XRD) studies reveal a spinel-type Face-Centered Cubic structure and a secondary Cr2O3 phase when x ≤ 0.75 and a Body-Centered Tetragonal structure when x = 1. Fourier Transform Infrared Spectroscopy (FT-IR) indicated two strong absorption bands corresponding to the metal-oxygen stretching from tetrahedral and octahedral sites, characteristic of spinel structure. Ultraviolet-Visible (UV-Vis) spectra exhibited the electronic transitions of the Cr2+ Cr3+ and Ni2+ ions. From the UV-Vis data, the CIE color coordinates, (x, y) of the pigments were evaluated. The morphology was examined by Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) showing the agglomeration behavior of the particles. The stability, coloring properties and potential ceramic applications of studied pigments were tested by their incorporation in matte and glossy tile glazes followed by the application of obtained glazes on ceramic tiles. This study highlights the change in pigment color (from turquoise to a yellowish green) with Ni2+ ions substitution in the CoCr2O4 spinel matrix.