Low temperature sintered of Bi2O3 deficient sillenite Bi12SiO20 ceramics

Bismuth oxide based Bi12SiO20 dielectric ceramics were prepared via a solid state reaction process. The bismuth oxide of the ceramics was vaporized during the calcination and sintering process, and became non-stoichiometric Bi2O3 deficient sillenite compounds. Different amounts of Bi2O3 were added to the sintered pellets in order to compensate for the loss of Bi2O3. The sillenite dielectric ceramics with different Bi2O3 additives were analyzed. Bismuth oxide Bi2O3 as a minor phase was detected from the Bi12SiO20 powders calcined at 750 degrees C, and there was approximately 0.89 wt% Bi2O3 vaporized after calcination. There was approximately 2 wt% Bi2O3 loss when the pellet was sintered. The relative densities of the sintered pellets decreased with increasing temperature, this was attributed to the vaporization of the Bi2O3 during sintering. The 780 degrees C sintered Bi12SiO20 pellet without Bi2O3 addition had the highest relative density, at roughly 98.7%. Dielectric constants of the sintered pellets with Bi2O3 additions lower than 4 wt% were ranged between 38.6 and 39.6, Q x f values of the sintered Bi12SiO20 pellets varied depending on the sintering conditions and Bi2O3 additions. The sample without Bi2O3 addition sintered at 820 degrees C for 10 h, had a dielectric constant epsilon(r) = 38.95, Q x f value = 14,910 (at 7.73 GHz) and temperature coefficient of resonant frequency t(f) = -25.3 ppm/degrees C. (C) 2016 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.