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, εr = 10 and 39, microwave quality factor, Qf 0 = 10800 and 2600 GHz, and temperature coefficient of resonant frequency, τf = −41 and −203 ppm/oC, respectively. The unusually large –ve τf, high εr 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 εr, +ve τf end members. Composites were, therefore, fabricated of x Bi 4 B 2 O 9 with (1−x) BaNd 2 Ti 4 O 12 (x BB – BNT ), and (1−x)[0.2 CaTiO 3−0.8( Li 0.5 Nd 0.5) TiO 3] (x BB – 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 0.075 BB – BNT with εr = 86, Qf 0 = 5400 GHz, and τf = 4 ppm/°C, and for 0.04 BB – CTLNT with εr = 127, Qf 0 = 2700 GHz, and τf = −4 ppm/°C. Unusually for composites, Qf 0 did not significantly deteriorate and εr 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.
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