High density Gd-substituted yttrium iron garnets by coprecipitation

Gadolinium-substituted yttrium iron garnets are ferrite materials of primary importance in microwave engineering. Stoichiometric powders of nominal composition Y2.6Gd0.4Fe5O12 (i.e. Fe/(Y + Gd) = 1.67) were prepared by reverse strike coprecipitation of metal nitrates. In order to investigate the influence of composition on phase formation, non-stoichiometric powders were also synthesised. On the basis of DTA/TGA analysis, dried coprecipitates were calcined between 600 degrees C and 1200 degrees C and then characterised by ICP, XRD and HT-XRD. Amorphous coprecipitates crystallise around 700 degrees C in cubic garnet phase along with small amounts of YFeO3 and/or alpha-Fe2O3. Only iron-rich garnets, either pure or Gd-substituted, calcined at 1200 degrees C or above display a single-phase cubic garnet. According to thermal dilatometry results, calcined powders were sintered in air up to 1470 degrees C. The microstructure of sintered ceramics is made up of fine grains, the average size ranging between 3 mu m and 13 mu m. Density of sintered bodies ranged from 88% to 98%. Ferromagnetic resonance linewidth (Delta H-3dB) ranged between 4352.9A m(-1) and 4392.7 A m(-1), depending on composition and microstructure. (C) 2007 Elsevier B.V. All rights reserved.