Bismuth borate composite microwave ceramics synthesised by different ratios of H3BO3 for ULTCC technology

Bi3B5+xO12 (+ 3x/2) (x= 0 similar to 6) compounds were fabricated by a conventional solid-state reaction method. The microwave dielectric properties, sintering behaviour, crystal structure, and phase evolution of the ceramics were investigated. All samples densified at ultra-low temperatures (575 similar to 700 degrees C). As x increased, the phase composition of the ceramics gradually changed from mixed Bi4B2O9 and Bi3B5O 12 phases to a single Bi6B10O24 phase. The ceramic with x = 4 exhibited the best microwave dielectric properties of epsilon(r) = 12.14, Q x f = 14,800 GHz, and tau(f) = - 72 ppm/degrees C at 625 degrees C. The microwave dielectric properties deteriorated as x increased further. Moreover, the ceramics were proven to cofire with Al and Ag, indicating that they are candidates for ultra-low-temperature cofired ceramic devices.