Mixture behavior and microwave dielectric properties of (1−x)CaWO4–xTiO2

Abstract

The microwave dielectric characteristics and mixture behavior of (1 − x)CaWO 4 -xTiO 2 ceramics prepared with conventional solid-state route were studied using a network analyzer and X-ray power diffraction, respectively. The CaWO 4 compound had good properties (low permittivity and high quality factor) for microwave applications, but it had a high negative temperature coefficient of resonant frequency (τ f = −53). Hence, in order to tune the dielectric properties, (1 − x)CaWO 4 -xTiO 2 were prepared for different values of x. X-ray powder diffraction and SEM analysis revealed that CaWO 4 and TiO 2 coexisted as a mixture. The mixture formation and dielectric properties could be explained by mixture rule. In particular, at x = 2.6, good microwave dielectric properties were obtained: Qf = 27,000, ε r = 17.48, and τ f = ∼0 ppm/ • C.

Microstructure and microwave dielectric properties of low-temperature sinterable (1 − x)Ba3(VO4)2–xCaWO4 composite ceramics

“…The e r value of the composite ceramics at the same sintering temperature was found to decrease with increasing the content of CaWO 4 . It also can be found that the dielectric constant of the (1 -x)Ba 3 (VO 4 ) 2 -xCaWO 4 composite ceramics is approximately in between those of single-phase Ba 3 (VO 4 ) 2 and CaWO 4 ceramics [7,8]. This is basically ascribed to the mixing rule of dielectrics as expressed by the Maxwell-Wagner's equation [17].…”

“…For all compositions, the maximum Q 9 f values can be obtained as the sintering temperature is 900°C, then begin to decline by further increasing the sintering temperatures up to 1,000°C. The Q 9 f values of all compositions roughly range from 21,600 to 37,000 GHz, which were lower than those of pure-phase Ba 3 (VO 4 ) 2 (Q 9 f = 42,000 GHz) and CaWO 4 (Q 9 f = 75,000 GHz) ceramics [6,7]. This result might be attributed to the doping effect that a slight amount of element such as Ca 2?…”

“…A near-zero s f value can be easily obtained by altering the relative contents of two phases. The 0.74CaWO 4 -0.26TiO 2 (volume fraction) composite ceramic sintered at 1,200°C, exhibits a s f value *0 ppm/°C, a e r value of 17, and a deteriorated Q 9 f value of 27,000 GHz [7]. TiO 2 has a high sintering temperature of 1,500°C, which tends to degrade the sinterability and microwave dielectric properties of the composite.…”

Phase structure and microwave dielectric properties of (1−x)Li2Zn3Ti4O12−xTiO2 ceramics

“…However, most of these ceramics have a large negative f value. Generally, there are two methods to design a material with a stable temperature coefficient: (1) composite materials by mixing component materials [8] with negative and positive f values, such as Zn 2 Te 3 O 8 -TiO 2 [9], Zn 2 TiO 4 -TiO 2 [10], Ca 2 P 2 O 7 -TiO 2 [11], CaWO 4 -TiO 2 [12], Mg 4 Ta 2 O 9 -TiO 2 [13] and LiNb 3 O 8 -TiO 2 [14]. (2) Formation of solid solutions, such as complex perovskites [15] and other systems [16][17].…”

Microwave dielectric properties of (1−x)ZnMoO4–xTiO2 composite ceramics

“…AWO 4 compounds have good dielectric properties: permittivity is 8-17, Q f value is 32,000-69,000 GHz, and f value is −53 to −78 ppm/ • C [5]. AMoO 4 compounds are also suitable for applications of microwave dielectric materials, with low permittivity (7)(8)(9)(10)(11), low dielectric loss (37,000-90,000 GHz) and relatively small temperature coefficient of resonant frequency (−57 to −87 ppm/ • C) [6] other systems [14][15][16][17]. In the recent investigation, ZnMoO 4 sintered at 800 • C presents excellent microwave dielectric properties with ε r = 8.67 (permittivity), Q f = 49,900 GHz, f = −87.49 ppm/ • C [6].…”