Hydrothermal Synthesis, Characterization and Magnetic Properties of Rare Earth Iron Garnets Sm_3Fe_5O_(12) and Eu_3Fe_5O_(12)

The rare earth iron garnets R3Fe5O12（R=Sm, Eu） were synthesized under mild hydrothermal conditions, and their crystal growth was found to be sensitive to alkalinity, reaction temperature and time. The as-prepared samples were characterized by powder X-ray diffraction（XRD）, scanning electron microscopy（SEM）, infrared spectra（IR） and Raman spectrum. The M vs. H loops and magnetic parameters have been traced with a vibrating sample magnetometer（VSM） and superconducting quantum interference devices（SQUIDs） magnetometer. We proposed the formation mechanisms and formulated a reasonable explanation for their growth habits. Different morphologic characteristics were observed by changing alkalinity in the reaction systems. The magnetic studies gave saturation magnetization（Ms） and Curie temperature（TC）. The magnetic behaviors of Sm3Fe5O12 and Eu3Fe5O12 in mild hydrothermal systems are comparable with those in high temperature solid state reactions.

Structural and Magnetic Studies of Ga-doped Yttrium Iron Garnet

Ga-doped Yttrium Iron Garnet (Y_(3)Ga_(x)Fe_(5-x)O_(12),Ga:YIG) was prepared by solid state reaction method and sintering at 1 300 ℃.Rietveld analysis of X-ray diffraction patterns indicated that all samples crystallized in a single cubic structure (space group Ia-3d) with decreasing lattice constant as Ga concentration increased.SEM surface micrograph images of YIG samples showed highly compacted grains with small reduction in the grain size with increasing Ga concentration.Raman spectroscopy measurements confirmed the replacement of Fe^(3+) ions by Ga^(3+) ions in the garnet structure was revealed by the observed blue shifts in Raman spectra.The saturation magnetization decreased from 28.2 to 4.98 emu g^(-1) with increasing x from 0.0 to 1.0 due to the preferential substitution of Ga^(3+) ions for Fe^(3+) ions at tetrahedral sites.Room temperature Mössbauer spectra for the samples revealed a reduction of the hyperfine field values for octahedral and tetrahedral sites,and the development of additional components with increasing Ga concentration.Analysis of the magnetic data and Mössbauer spectra confirmed that spin canting in the substituted garnets plays an important role in explaining the observed reduction of the saturation magnetization as x increased.

Combustion synthesis of YAG:Ce phosphors via the thermite reaction of aluminum

Cerium-doped yttrium aluminum garnet（YAG：Ce） as a yellow phosphor for white light-emitting diodes（LEDs） was synthesized via a facile combustion method using Y2 O3, CeO2, Al2 O3, Al,and NaClO4 as raw materials. The combustion synthesis approach utilizes the strong exothermic oxidation of aluminum to realize a self-sustaining reaction. In this study, we investigated the effects of the ratios of Al2 O3 to AI,fluxes, and coprecipitated materials as raw materials on the luminescence properties of the synthesized YAG：Ce phosphors. When the amount of Al2 O3 x is varied, the combustion reaction proceeds at x ≤ 1.8,with x = 1.725 being the optimum condition for producing a high-performance product. When 5 wt%BaF2 is added, the luminescence intensity is significantly improved owing to a decrease of YAP（YAlO3）formation with improved uniformity. However, the addition of CaF2 and NaF does not improve the luminescence properties. To suppress the segregation of CeO2, we used the coprecipitated material Y2 O3-CeO2 as a raw material. Unlike with separate addition of Y2 O3 and CeO2, Ce ions are uniformly distributed in the coprecipitated material, resulting in improved luminescence properties. The combination of BaF2 and coprecipitated material significantly improves the internal quantum efficiency to83.0%, which is close to that of commercial phosphors.