Microwave and terahertz properties of porous Ba4(Sm,Nd,Bi)28/3Ti18O54 ceramics obtained by sacrificial template method

MSO 4 (M = Ca, Sr, Ba) ceramics with relative densities exceeding 96% were prepared by solid-state sintering at low sintering temperatures of 625-875 • C, and their structures and microwave dielectric properties at 10-19 GHz were characterized. MSO 4 ceramics crystallized in orthorhombic symmetry with the space groups of Amma for CaSO 4 and Pnma for SrSO 4 and BaSO 4 . The optimal microwave dielectric properties were obtained with ε r = 5.85, Qf = 57 000 GHz, τ f,W = −98.8 ppm/ • C for CaSO 4 , ε r = 10.95, Qf = 15 500 GHz, τ f,W = 101.6 ppm/ • C for SrSO 4 , and ε r = 9.42, Qf = 38 200 GHz, τ f,W = −4.7 ppm/ • C for BaSO 4 . The increased ε r and τ f,W while decreased Qf value in the order of CaSO 4 , BaSO 4 , and SrSO 4 were attributed to the enhanced rattling effect of M 2+ . Besides, the temperature dependence of τ f was weak for CaSO 4 and BaSO 4 , whereas much stronger for SrSO 4 . As most low-ε r microwave dielectric ceramics are of large negative τ f , the near-zero τ f of BaSO 4 and positive τ f of SrSO 4 are rare, indicating they are potential candidates for millimeter-wave communication as a temperaturestable dielectric ceramic and a compensator for tuning negative τ f to near-zero, respectively.

Section: Resultsmentioning

confidence: 99%

MSO₄ (M = Ca, Sr, Ba) microwave dielectric ceramics with low dielectric constant

Ying

Luo

et al. 2022

“…34 Notably, high 𝜀 𝑟 ceramics often have higher dielectric loss, but introducing air into the composite can effectively reduce this loss, leading to an increase in 𝑄 × 𝑓. 35 As shown in Figure 5, the 𝑄 × 𝑓 values for (1 − x)NBM-xBM ceramics, where x = 0.3-0.6, sintered at varying temperatures for 4 h. At 600 • C, the 𝑄 × 𝑓 value is higher in comparison to the denser ceramics, possibly due to the low permittivity (ε air ≈ 1) and low dielectric loss of air (tanδ ≈ 0). Hence, if the ceramic were to consider as composite and air, the air might bring some positive effect that would increase the 𝑄 × 𝑓 value.…”

Section: St (mentioning

confidence: 99%

Microwave dielectric properties of (Na_0.5Bi_0.5)MoO₄–BaMoO₄ composite ceramics with ultralow sintering temperature

Alzakree,

Wang,

Shehbaz

et al. 2024

The rapidly ever‐growing wireless communication demands development of low loss, ultralow sintering temperature dielectric ceramics with excellent microwave properties. In this work, fabrication and properties of novel microwave dielectric composite ceramics (1 − x)(Na0.5Bi0.5)MoO4–xBaMoO4 (x = 0.3–0.6), in short as ((1 − x)NBM–xBM), synthesized via solid‐state reaction method with an ultralow sintering temperature is reported. X‐ray diffraction analysis confirms the coexistence of both (Na0.5Bi0.5)MoO4 and BaMoO4 scheelite phases. Scanning electron microscopy analysis demonstrated dense microstructures of ceramics sintered at 650°C and 700°C. The dielectric properties of (1 − x)NBM–xBM (x = 0.3–0.6) ceramic are significantly tailored by incorporation of BaMoO4. With the increase in x from 0.3 to 0.6, the (1 − x)(Na0.5Bi0.5)MoO4–xBaMoO4 displays noticeable change in microwave permittivity (varying from 25.4 to 16.6), quality factor values, and temperature coefficient of frequency (range tunable from +37.6 ppm/°C to −14.2 ppm/°C). The microwave dielectric ceramic, 0.5(Na0.5Bi0.5)MoO4–0.5BaMoO4, has optimum dielectric properties (, = 15 164 GHz, τf = −0.2 ppm/°C) at sintering temperature of 650°C. The dielectric resonator antenna designed using (1 − x)(Na0.5Bi0.5)MoO4–xBaMoO4 ceramics demonstrated excellent radiation performance at resonance frequency of 5.905 GHz, gain of ∼5.8 dBi and 140 MHz bandwidth, which validates its microwave applications utilization within the field of ultralow temperature cofired ceramics technology.

“…4,5 As reported, microwave dielectric ceramics are widely used in the fabrication of microwave devices such as antennas, filters, and resonators, 4,6,7 and some of them have excellent dielectric properties in terahertz frequency range. [8][9][10] Moreover, porous structures can reduce both 𝜀 r and tanδ. 11,12 Therefore, highly porous microwave dielectric ceramics may be suitable materials for 6G telecommunication.…”

Section: Introductionmentioning

confidence: 99%

High‐strength ceramic foams with ultralow dielectric constant and loss in terahertz frequency region

Chen

Guo

et al. 2022

Sixth generation (6G) wireless networks operating in terahertz frequency region are significant solutions to the increasing number of telecommunication devices and the demand for faster data transmission. However, few dielectric materials exhibiting an ultralow relative dielectric constant (εr), loss tangent (tanδ), and high mechanical strength are found suited for 6G telecommunication. In this study, we developed lightweight ceramic foams by directly sintering glass hollow spheres. The effects of sintering temperatures on their mechanical performance, and terahertz optical and dielectric properties were systematically investigated. The final compositions of ceramic foams contain glass, cristobalite, quartz, and wollastonite. The crystalline content increases with increasing sintering temperature. The ceramic foams sintered at low temperatures of 700–850°C exhibit a high porosity ranging from 74.6% to 87.3%, ultralow εr ranging from 1.41 to 1.83, and tanδ of ∼0.011 at 0.5 THz, as well as high compressive strength ranging from 10.1 to 27.4 MPa, which could be promising materials for 6G telecommunication.