Search

(1 − x)CoWO-xCuO dielectric ceramics were synthesized by the mixed oxide reaction method. W-based microwave dielectric materials with excellent properties have been reported heavily. The high sintering temperature seriously limited their commercial application in low temperature co-fired ceramics (LTCC) devices. CuO with a low melting point had been widely used as a liquid phase sintering aid. The addition of CuO had great effects on the sintering temperature, microstructure and microwave dielectric properties. When a small amount of CuO was added, the optimal sintering temperature could be decreased from 1200 to 950 °C, with no severe deterioration on the dielectric properties. The X-ray diffraction patterns indicated all samples to exhibit wolframite-like monoclinic P2/c (13) structure and no impurity phase. X-ray powder diffraction and SEM analysis revealed the formation of solutions between CoWO and CuO. Meanwhile, excellent microwave dielectric properties were obtained (permittivity of ~10.69, quality factor Q × f of ~20,000 GHz ( f = 10 GHz) and temperature coefficient of frequency τ of ~−35 ppm/°C) for 0.97CoWO-0.03CuO sintered at 950 °C. These features make (1 − x)CoWO-xCuO ceramics a promising candidate for LTCC application. [ABSTRACT FROM AUTHOR]

A novel lead-free, high dielectric constant, ultra-wide temperature stable dielectric ceramic Ba 1−x Bi x Ti 1−x −y Zn 0.75x W 0.25x+y O 3+y (0.22≤x≤0.30, y=0.015) was synthesized by the traditional solid-state reaction method. The phase composition, electric and dielectric properties of the Ba 1−x Bi x Ti 1−x −y Zn 0.75x W 0.25x+y O 3 ceramics were investigated. The P-V-L dielectric theory was introduced. And, the chemical bond energy was calculated to track the changes in micro-structure. The relationships between chemical bond energy and the macroscopic dielectric properties(ε r , dielectric stability and dielectric loss ) in Ba 1−x Bi x Ti 1−x−y Zn 0.75x W 0.25x+y O 3+y ceramics were discussed systematically. Owing to the inhomogeneous micro-structure and the diffusion in phase transition, Ba 1−x Bi x Ti 1−x−y Zn 0.75x W 0.25x+y O 3+y ceramics showed a stable permittivity (~800±15%) over a ultra-wide temperature range (−30 to 375 °C). Moreover, dielectric loss was less than 0.02 and the insulation resistance was over 10 12 Ω cm. These features suggested that the Ba 1−x Bi x Ti 1−x−y Zn 0.75x W 0.25x+y O 3+y ceramic could be considered as a promising candidate material for energy storage applications in harsh environment. [ABSTRACT FROM AUTHOR]

Low-loss (Zn 1- x Ni x )ZrNbTaO 8 (0.02 ≤  x  ≤ 0.10) ceramics possessing single wolframite structure are initiatively synthesized by solid-state route. Based on the results of Rietveld refinement, complex chemical bond theory is used to establish the correlation between structural characteristics and microwave performance in this ceramic system. A small amount of Ni 2+ ( x  = 0.06) in A-site with the fixed substitution of Ta 5+ in B-site can effectually raise the Q  ×  f value of ZnZrNb 2 O 8 ceramic, embodying a dense microstructure and high lattice energy. The dielectric constant and τ f are mainly affected by bond ionicity and the average octahedral distortion. The (Zn 0.94 Ni 0.06 )ZrNbTaO 8 ceramic sample sintered at 1150 °C for 3 h exhibits an outstanding combination of microwave dielectric properties: ε r = 27.88, Q × f  = 128,951 GHz, τ f = –39.9 ppm/°C. Thus, it is considered to be a candidate material for the communication device applications at high frequency. [ABSTRACT FROM AUTHOR]