Low Sintering Temperature Microwave Dielectric Ceramics and Composites Based on Bi₂O₃ –B₂O₃

Abstract

Phase evolution, sintering behavior, and microwave dielectric properties of compounds within the Bi 2 O 3 -B 2 O 3 phase diagram have been investigated. Two promising ceramics, Bi 6 B 10 O 24 and Bi 4 B 2 O 9 , were fabricated which densified at 700°C and 660°C with permittivity, e r = 10 and 39, microwave quality factor, Qf 0 = 10800 and 2600 GHz, and temperature coefficient of resonant frequency, τ f = À41 and À203 ppm/ o C, respectively. The unusually large -ve τ f , high e r and reasonable values of Qf 0 of Bi 4 B 2 O 9 coupled with its low sintering temperature suggested that it may be useful in the fabrication of temperature-stable composites with high e r , +ve τ f end members. Composites were, therefore, fabricated of xBi 4 B 2 O 9 with (1Àx)BaNd 2 Ti 4 O 12 (xBB-BNT), and (1Àx)[0.2CaTiO 3 À0.8(Li 0.5 Nd 0.5 )TiO 3 ] (xBB -CTLNT), respectively (x is in wt%). In each case, the sintering temperature to achieve > 95% theoretical density was reduced by ! 150°C to 1200°C. Optimum properties were achieved for 0.075BB-BNT with e r = 86, Qf 0 = 5400 GHz, and τ f = 4 ppm/°C, and for 0.04BB-CTLNT with e r = 127, Qf 0 = 2700 GHz, and τ f = À4 ppm/°C. Unusually for composites, Qf 0 did not significantly deteriorate and e r increased markedly with respect to the high-permittivity end-member for composites with x < 0.1. Optimized compositions are suitable for applications in dielectrically loaded antennas and in C0G high-frequency filter applications. C. A. Randall-contributing editor

Enhancing Properties in Microwave Ceramics Using a Designer Sintering Aid

“…It should be noted that previous work by Chen et al. has shown the appearance of unidentified secondary phases at x ≥ 7.5 wt% …”

Low-temperature Sintering of Bi2O3-B2O3 Glass Doped Li2ZnTi3O8 - Li2TiO3 Ceramic and Its Dielectric Properties

“…20 According to previous studies, BBO glass possesses a negative τƒ value about −41～−203 ppm/℃. [22][23][24] Therefore, the τƒ value in this system can be tuned from positive to negative by changing the www.ijm-me.org…”

“…It can be successfully applied in lowering the sintering temperatures of various ceramics, such as Ca[(Li1/3Nb2/3),Ti]O3-δ, BaTiO3, and Ca2MgSi2O7. [22][23][24][25][26] However, to the best of our knowledge, BBO glass addition has not been reported in Li2ZnTi3O8-Li2TiO3 system so far. In this work, the phase composition, the microstructure, and the microwave dielectric properties of 0.65Li2ZnTi3O8-0.35Li2TiO3 (LZT) ceramic doped with BBO glass will be investigated in detail.…”

“…In addition, the decrease of Q×f value may be related the relatively lower Q×f value of BBO (about 2000～10,800GHz) relative to that of LZT (more than 50,000 GHz). 21,24 Notably, when the BBO content added in LZT ceramic exceeds 5wt%, the excessive liquid phase and the unknown second phase may deteriorate the microwave dielectric properties of the ceramic, which leads to a low Q×f value. To sum up, the LZT ceramic with 0.5wt% BBO addition sintered at 840℃ shows good microwave dielectric properties of εr = 26.6, Q×f = 40,683GHz and τƒ = +1.0ppm/℃.…”

Microwave dielectric properties of La5(Ti4B)O17 and Nd5(Ti4B)O17 (B = Cr, Fe) ceramics

“…In addition to e r , the other two parameters important for microwave applications are a high quality factor (Q 9 f o ) for fine tuning and near zero temperature coefficient of resonance frequency (s f ) for thermal stability [8]. For example, for application as dielectrically loaded antennae cores, a dielectric materials must exhibit 20 B e r B 85, Q 9 f o [ 5,000 GHz, and s f = ± 10 ppm/ o C [9]. CaLa 4 Ti 5 O 17 is an A 5 B 5 O 17 type compound and has been reported to exhibit a high e r and Q 9 f o but its -ve s f is too high for commercial applications [10].…”