Synthesis and Characterization of Gadolinium Oxide-Hematite Magnetic Ceramic Nanostructures

Mixed-oxide nanostructures of the type xGd2O3-(1-x)α-Fe2O3 (x=0.1, 0.3, 0.5 and 0.7) were synthesized by mechanochemical activation for ball milling times of 0, 2, 4, 8 and 12 hours. The systems were subsequently analyzed by Mӧssbauer spectroscopy, X-ray powder diffraction (XRPD), magnetic measurements and optical diffuse reflectance spectroscopy. The magnetic hyperfine field was studied as function of ball milling time for all sextets involved and found to be consistent with the formation of a limited solid solution in the systems investigated. The end-product was the gadolinium perovskite, represented by a doublet whose abundance was derived as function of the milling time. The XRPD patterns recorded for the equimolar composition were dominated by the diffraction peaks of GdFeO3 after 12 hours of milling. The hysteresis loops were recorded at 300 and 5 K in an applied magnetic field of 5 T and were interpreted as a superposition of paramagnetic behavior of gadolinium oxide and weak ferromagnetic behavior of hematite and gadolinium perovskite. The Morin transition of hematite was inferred from zero-field-cooling-field-cooling (ZFC-FC) curves measured with a magnetic field of 200 Oe in the 5-300 K temperature range and was found to depend on the ball milling time. Optical diffuse reflectance spectra showed that the compounds were semiconductors with an optical band gap of 2.1 eV.

Phase Constitution in Mixed Gd_2O_3 and B_4C by Sintering at High Temperature

The phase constitution in mixed Gd2O3 and B4C by sintering in graphite tube furnace at the temperature of 100～1489 ℃ in argon atmosphere was studied by means of XRD and TG-DTA. The results show that the impurity C reacts with O in the B4C at the temperature of 367～458 ℃. When the temperature is 800 ℃, Gd2O3 reacts with B4C, and the reaction products include GdB6, GdB4, GdBO3, GdBC and B. GdBC changes into GdB4 at 1200 ℃. When the temperature is 1470 ℃, GdB6 is obtained by the reaction of GdB4 with elemental B. The content of GdB6 is increasing with the prolonging time.

Structure and Waveguide Properties of Sol-Gel Derived Gd_2O_3 Films

Pure and rare earth doped gadolinium oxide (Gd 2O 3) waveguide films were prepared by a simple sol-gel process and dip-coating method. Structure of Gd 2O 3 films annealed at different temperature was investigated by X-ray diffraction and transmission electron microscopy. Oriented growth of (400) face of Gd 2O 3 has been observed when the films were deposited on amorphous substrate. The refractive index and thickness of films were determined by m-lines spectroscopy. The laser beam (λ=632.8 nm) was coupled into the film by a prism coupler and the propagation length is about 3.5 cm. Luminescence properties of europium ions doped films were measured by waveguide fluorescence spectroscopy, which shows disordered environment for Eu 3+ at 400 ℃.

Preparation and Photocatalytic Activity of Nanocrystalline GdFeO_3

With Gd2O3, Fe （NO3）3· 9H2O, and nitric acid （ 1： 1 volume fraction） as starting materials, nanocrystalline material of rare-earth composite oxide GdFeO3 with perovskite-type structure was synthesized by sol-gel method in the system of citric acid. Structural characteristics were characterized by XRD and TEM, which indicate that the sample is nanocrystallite with uniform grain size distribution and the average grain size is about 21 nm. Its crystal structure includes a certain amount of lattice distortion due to decrease of grain size and increase of surface area. Photocatalytic properties of this material were tested by decolorization of various water-soluble dyes. Effects of irradiation time and amount of GdFeO3 on photocatalytic activity were also investigated. The results show that nano-sized GdFeO3 exhibits high photocatalytic activity and that increase of irradiation time and the amount of GdFeO3 can improve its photocatalytic activity.

Synthesis and characteristics of transparent Gd_(2)O_(3)ceramics with cubic structure

Transparent Gd_(2)O_(3)ceramics with a cubic crystal structure were successfully synthesized for the first time.The Gd_(2)O_(3)ceramics subjected to hot isostatic press(HIP)at 1070℃consisted of uniform grains of 2-3μm,and only a few residual pores could be detected inside the materials.X-ray diffraction(XRD)shows that the obtained polycrystalline materials have a cubic crystal structure,and the transmission polarized light observation shows that there is no birefringence inside the materials,indicating inherent optical properties of the cubic crystal structure.The optical absorption edge is 640 nm(optical band gap:2.1 eV),and the transmittance in the visible to near-infrared region is 72%,which is close to the theoretical transmittance calculated from Fresnel loss.Verdet constant of this material is almost wavelength-independent,and it is diamagnetic since it has the opposite polarity to that of common paramagnetic materials.

Spectroscopic properties of Gd_2O_3:Dy^(3+)nanocrystals

Gd203：Dy3＋ nanocrystals were synthesized via solvothermal method followed by a subsequent calcination. The samples were characterized by X-ray diffraction （XRD）, transmission electron microsopy （TEM）, Electronic dispersive X-ray spectroscopy （EDX）, photoluminescence （PL） spectrum and decay curves. The effect of the annealing temperature on the crystallinity and particle size was studied; heat treatment improved the crystallinity of as-prepared nanocrystals as well as increased their particle size. The nanocryatals presented monodispersed spherical shape under TEM. Photoluminescence spectra showed that nanocrystal exhibited strong yellow emission corresponding to 4F9/2----6HI3/2 transition （573 nm） of Dy3＋ under UV light excitation, which broadened with the particle size decreased without structure changed. The theoretical mechanism of luminescence was explored and surface effect was thought to be the main reason.