Synthesis of Al3Fe5O12 Cubic Structure by Extremely Low Sintering Temperature of Sol Gel Technique

Fabrication of nano materials particularly nano inductors at low
sintering temperature remains a challenge. This study was carried out as our initial response to obtain a
nano-size inductors, which is aluminium iron garnet using low sintering temperature. Approach: The
aluminum iron garnet (Al3Fe5O12) nano crystals were prepared by sol-gel technique. The starting
solution is a mixture of iron nitrate Fe(NO3)3.9H2O, yttrium nitrate Y(NO3)3.6H2O and aluminum
nitrate Al(NO3)3.9H2O and were dissolved in 150 mL of citric acid, C6H8O7.H2O. The mixtures were
stirred continuously, at about 250 r.p.m, in room temperature until the formation of a gel was
observed. The gel was dried at 110°C in an oven to remove the unneeded water. The dried powder was
calcined at 600°C, for 3 h in air and was wet crushed using a Fritsch Planetary Micromill for 6 h to
obtain fine particles powder. The sample was then characterized by X-Ray Diffraction analysis
(XRD) to confirm the garnet phase. The sintered powder was characterized at different
temperature by X-ray diffraction analysis and Raman Spectroscopy was used to study the
vibration of atoms in a materials. Finally, Field Emission Scanning Electron Microscopy
(FESEM) was used to study the surface morphology of the sample. Results: The XRD results
showed that, the best garnet cubic phase giving [1 0 4] plane of the Al3Fe5O12 crystallite appeared at
33.30 of the 2 theta. We report a clear cubic crystal structure of less than 62 nm, which was
observed possible for the first time, for this type of garnet, Al3Fe5O12. The much lower sintering
temperature 800°C comparing to the conventional method was attributed to the sol gel method.
Conclusion: The long stirring time (one month) that had allowed self assembly of the anions and
cations to form the gelatin. In addition the small radius of aluminium prefers to occupy the
tetrahedron and octahedron sites instead of the much larger dodecahedron site resulted to the clear
cubic structure of the garnet.