Ultralow-Temperature Synthesis and Densification of Ag₂CaV₄O₁₂ with Improved Microwave Dielectric Performances

Abstract

At extremely low temperatures, Ag 2 CaV 4 O 12 was easily synthesized using the traditional solid-state approach. With a low relative permittivity (ε r ) of 7.52, a high quality factor (Q × f) of 48 800 GHz (f = 13.6 GHz), and a temperature coefficient of resonance frequency (τ f ) of −77.4 ppm/°C, dense ceramics sintered at 480 °C with outstanding microwave dielectric characteristics were attained. By combining with rutile TiO 2 , a composite ceramic with balanced microwave dielectric properties (τ f = 3.2 ppm/°C, ε r = 10.96, and Q × f = 49 081 GHz) was achieved. No chemical reaction between Ag 2 CaV 4 O 12 and silver and aluminum occurred. All of the findings show that Ag 2 CaV 4 O 12 has the potential to be used as dielectric resonances in wireless communication and as substrates in low-temperature cofired ceramics. Furthermore, the processing at an ultralow temperature of Ag 2 CaV 4 O 12 shows that it is extraordinarily energy saving from the point of view of fabrication and might allow for room-temperature synthesis by combining with high-energy mechanical milling or sintering using a high pressure such as hot isostatic pressing (HIP), spark plasma sintering (SPS), and cold sintering (CS).

Novel Tri-rutile Ni0.5Ti0.5TaO4 Microwave Dielectric Ceramics: Crystal Structure Chemistry, Raman Vibration Mode, and Chemical Bond Characteristic In-Depth Studies

“…The enhanced density originated from grain growth, which fits well with the microstructural evolution (see Figure a–d). A similar trend was appeared in some other microwave dielectric materials, such as Ag 2 CaV 4 O 12 , Sr 3 VO 8 , Li 2 ZnGeO 4 , and AgPb 2 Mg 2 V 3 O 12 . − …”

Principal element design of garnets to access structure stability and excellent microwave dielectric properties

“…It is common knowledge that increasing the sintering temperature increases mass transfer, which promotes densification and shrinkage of ceramics. However, when the sintering temperature is too high, over‐sintering would occur, which is responsible for the abnormal grain growth or loss of the volatile elements (e.g., Li + , Na + , K + , Zn 2+ ) and results in the decreased bulk density 24 . Therefore, combining the change of diameter shrinkage and bulk density, the optimum sintering temperature was determined as 1280°C where the maximum bulk density of 4.18 g/cm 3 (∼98.47% of the theoretical density) for Ca 3 MgTiGe 3 O 12 was achieved.…”

“…However, when the sintering temperature is too high, over-sintering would occur, which is responsible for the abnormal grain growth or loss of the volatile elements (e.g., Li + , Na + , K + , Zn 2+ ) and results in the decreased bulk density. 24 Therefore, combining the change of diameter shrinkage and bulk density, the optimum sintering temperature was determined as 1280 • C where the maximum bulk density of 4.18 g/cm 3 (∼98.47% of the theoretical density) for Ca 3 MgTiGe 3 O 12 was achieved. By comparison, the Zn-based counterpart exhibited a much lower densification temperature of 1180 • C with a much higher bulk density of 4.47 g/cm 3 (∼98.76% of the theoretical density).…”

Entropy regulation in LaNbO4-based fergusonite to implement high-temperature phase transition and promising dielectric properties

“…Microwave dielectric ceramics are indispensable materials in the field of communication, which are widely used in mobile communication, radar, satellite positioning, and navigation systems [1,2].…”

“…The configuration entropy (Sc) of the system can be calculated according to the Eq. (1) [7]： 𝑆𝑆 𝑐𝑐 = −𝑅𝑅 ∑ 𝑥𝑥 𝑖𝑖 𝑙𝑙𝑙𝑙(𝑥𝑥 𝑖𝑖 ) 𝑛𝑛 𝑖𝑖=1 (1) where xi is the concentration of the ith component and R is the gas constant in the ideal state. According to the magnitude of the Sc value, the system is generally divided into low-entropy (Sc ≤ 1.0R), mediumentropy (1.0R＜Sc≤1.5R), and high-entropy (Sc＞1.5R) [8,9].…”