Synthesis of coral-shaped yttrium-aluminium-iron garnets by solution-combustion method

Aluminium substituted yttrium-iron garnet (Y3AlxFe5−xO12, x = 0, 1, 2, 3, 4 and 5) powders were synthesized by solution combustion route followed by calcination at 1000 °C for 6 h. According to the X-ray diffraction (XRD) results, the as-prepared samples were amorphous. Calcination of the samples at 1000 °C for 6 h results in the formation of phase pure (Ia3̅d) garnet structure. The morphology of the samples (for all compositions) were found to be coral-network-like. The Rietveld refinement of the XRD patterns and the Mössbauer spectroscopy confirmed that Y3+ ions occupy the dodecahedral site, whereas Al3+ and Fe3+ ions are distributed in the tetrahedral and octahedral sites of the bcc (Ia3̅d) structure of the garnet phase. The Al3+ ions have a preference to occupy the octahedral site. The lattice parameter decreases with increase in Al-content due to the small size of the Al3+ cations. For the yttrium-iron-garnet (YIG) sample (x = 0), a saturation magnetization (MS) value of ~ 29 emu/g was obtained, which decreases to ~ 7 emu/g for the sample with x = 2. Further addition of Al makes the garnets paramagnetic. The coral network shape of our garnet samples renders them useful for various applications in catalysis.