Synthesis and characterization of Al-doped manganese ferrite uniform particles for high-frequency applications

The current study demonstrates the effect of partial substitution of Fe3+ with Al3+ ions in uniform manganese ferrite nanoparticles, MnAlxFe2-xO4, (where x = 0.0, 0.2, 0.6 and 1.0), on ferritization temperature, phase changes, crystallographic properties, morphology, and dielectric properties. In case of the pure sample, the X-ray diffraction pattern indicates the presence of a secondary alpha-hematite phase along with the major spinel ferrite and the scanning electron micrographs reveal high-degree polydispersity in size and morphology of particles because of the uncontrolled growth being occurred during calcination at 1000 degrees C. Interestingly, the incorporation of Al3+ ions to the sample is found to promote single spinel phase formation at lower temperature by increasing ionic mobility and stimulating solid-solid interactions between the metal oxides. The presence of Al3+ ions control the particle morphology by preventing abnormal grain growth, and thus a monodisperse particles system results. The crystallite size decreases linearly with an increase in Al3+ content in the sample because of the smaller ionic radius of Al3+ as compared to Fe3+ ion. Calculated crystallographic properties of the test samples are discussed for the difference in ionic radii of the replacing ions. The dielectric constant (epsilon') and dielectric loss (tan delta) of all the samples as a function of frequency at room temperature is determined and discussed. The AC conductivity (sigma(AC)) linearly increases with frequency due to the involvement of small polarons in the conduction mechanism. The significantly low dielectric loss values of Al-doped manganese ferrite nanoparticles make them a promising candidate material for high-frequency applications. (C) 2018 Elsevier B.V. All rights reserved.