No abstract

Monodispersed yttrium aluminum garnet (YAG) powders have been synthesized via homogeneous precipitation method from the mixed solutions of yttrium nitrate, aluminum nitrate, and ammonium aluminum sulfate using urea as the precipitant. The molar ratio of aluminum nitrate to ammonium aluminum sulfate has a significant effect on morphology and particle size of the precursor powders. It was found that spherical precursor particles can be obtained when the ratio is 1:1. During the homogeneous precipitation process, aluminum ions precipitate first and form monodispered spherical powders, and then yttrium ions precipitate onto the surface of the existing spheres. Monodispersed spherical YAG particles with 500 nm in diameter were obtained by calcining the precursor powder at 1100°C for 5 h. The so-prepared monodispersed spherical Nd:YAG powders have good sinterability, and can be sintered into transparent ceramics by vacuum sintering at 1650°C for 3.5 h.

Treating freshly prepared cerous hydroxide with hydrogen peroxide (H 2 O 2 ) under ambient conditions provides a facile and efficient way for converting CeO 2 nanoparticles (∼22 nm, 37 m 2 /g) into nanowires of fine diameters (down to ∼5 nm) and outstanding specific surface areas (∼184 m 2 /g). The CeO 2 nanomaterials were examined by XRD, BET, FT-IR, TG, HR-TEM, Raman scattering, and UV-vis absorption spectroscopy. The results show that the nanowires are single crystalline and of high purity and low defect (oxygen vacancy) concentration and are growing perpendicular to {220} planes. The CeO 2 nanowires show indirect and direct band gaps of ∼2.37 and 2.91 eV, respectively, which are both ∼0.15 eV lower than those observed from the nanoparticle form (∼22 nm) for the respective interband transitions. The CeO 2 nanowires were proposed to grow via a dissolution-reprecipitation mechanism, with an unstable Ce(OH) 3 O • OH hyperoxide intermediate as the template.

Abstract-A broadband dual-polarized four-port (DPFP) antenna is presented in this paper, which consists of a radiation element and a feed network. It is very compact in size, with the diameter of 150.0 mm and the height of 47.0 mm, with the following unique properties: (1) it has hybrid beam-forming capability and operates at two modes, which depends on its excitation; (2) its operating frequency range is from 0.96 to1.78 GHz, and the return loss is about 10 dB; (3) its insertion loss is (3 ± 0.5) dB, with its balanced power splitting over the relative bandwidths of 37% at Mode 1 (180 • ± 5 • phase shifting) and 55% at Mode 2 (±5 • phase shifting), respectively; (4) an isolation of 30 dB at Mode 1 is obtained between the dual polarized ports, with the gain of 7.6 dBi and 42 • of the 3 dB-bandwidth at 1.25 GHz; and (5) the gain difference between Modes 1 and 2 is about 7 dB, within the angle of −15 • ≤ θ ≤ 15 • for the same polarization at 1.25 GHz. For the application of DPFP, a hybrid beam forming algorithm is proposed with an angular precision of 7 • and is validated by measurement.