Haihong Xi

Phase composition, crystal structure, infrared reflectivity and microwave dielectric properties of temperature stable composite ceramics (scheelite and zircon-type) in BiVO4–YVO4 system

(1 − x)BiVO4–xYVO4 (x ≤ 0.65) ceramics were prepared using the solid state reaction method. X-ray diffraction, Raman spectra and scanning electron microscopy techniques were employed to study the phase composition and crystal structure. The ceramic samples were composed of both monoclinic scheelite and tetragonal zircon-type phases. The best microwave dielectric properties, with a permittivity ∼45, a Qf value 14 000 GHz and a temperature coefficient of resonant frequency (TCF) +10 ppm °C−1, were obtained in the 0.81BiVO4–0.19YVO4 ceramic sintered at 870 °C for 2 h. Far-infrared spectra study showed that Bi–O oscillations dominate microwave dielectric polarizations in the (1 − x)BiVO4–xYVO4 ceramics. The (1 − x)BiVO4–xYVO4 ceramics might be potential candidates for microwave devices application and low temperature co-fired ceramic technology (LTCC).

Microwave Dielectric Properties of Sol-Gel Processed Bi4Si3O12 Ceramics and Single Crystal

Microwave dielectric ceramics Bi4Si3O12 was made from powders prepared via sol-gel method as a potential candidate of low temperature co-fired ceramics in microwave applications. The microwave dielectric properties of sol-gel processed Bi4Si3O12 ceramics were compared with that of single crystal. The sintering temperature of the ceramics ranged from 920° to 1010°C. The best microwave dielectric properties were obtained when the ceramics was sintered at 980°C for 8 h with a permittivity of ∼8.8, a Q×f value of ∼41,898 GHz (at 11.5 GHz) and a temperature coefficient value of –72 ppm/°C. The permittivity, Q×f value, and temperature coefficient value of Bi4Si3O12 single crystal were ∼15.9, 45,326 GHz (at 7.0 GHz) and –92 ppm/°C, respectively.

Sol–gel preparation and luminescent properties of red-emitting phosphor Sr-Ba-Mo-W-O-(Eu3+,Sm3+)

Two series of red-emitting phosphors Sr-Ba-Mo-W-O:Eu,Sm and Sr-Ba-Mo-W-O:Eu have been synthesized by a sol-gel method. The effects of the chemical composition, concentrations of Sm(3+) and Eu(3+), the Sr(2+)/Ba(2+) ratio, and the W(6+)/Mo(6+) ratio on the luminescent properties were investigated. The as-prepared phosphors were characterized by X-ray diffraction and Raman spectra. Results showed that single phases of the two series were prepared. The compositions of Sr0.6 Ba0.13Mo0.8 W0.2O4:Eu0.10Sm0.08 and Sr0.75Ba0.1Mo0.8 W0.2O4:Eu0.10 had the strongest luminescent intensity. The excitation spectra of Sm(3+), Eu(3+) co-doped phosphors were broader and the strongest peak moved to 404 nm when compared with that of Eu(3+) single-doped phosphors. The luminescent intensity of the Sr0.6Ba0.13Mo0.8W0.2O4:Eu0.10 Sm0.08 at 618 nm were 2.8 times greater than that of Sr0.75Ba0.1Mo0.8 W0.2O4:Eu0.10. The luminescent intensity of Sr0.6Ba0.13Mo0.8 W0.2 O4:Eu0.10Sm0.08 and Sr0.75Ba0.1Mo0.8W0.2O4:Eu0.10 at 150 °C decreased to 56.8% and 50.3% of the initial value at room temperature, respectively.

Luminescent properties of sol–gel processed red‐emitting phosphor Ca0.6Sr0.4–1.5x‐0.5yMo0.4 W0.6O4:EuxLiy

A series of red-emitting phosphors Ca0.6Sr(0.4-1.5x-0.5y)Mo0.4W0.6O4:Eux Liy (x = 0.02-0.12, y = 0-0.12) has been synthesized by a sol-gel method. The effects of calcining temperature, concentrations of Li(+) and Eu(3+) , and compensation ions on the luminescent properties were investigated. X-ray diffraction and scanning electron microscopic results showed that as-prepared phosphors were of single phase with several microns. The Li(+) compensated compositions showed remarkably intense red emission at 619 nm. The emission intensity of the series reached maximum for compositions at x = 0.08 and y = 0.08 when the calcining temperature was 900 °C.