Preparation and Characterization of Bi_2Ti_2O_7 Microwave Dielectric Ceramics by Citrate Sol-Gel Method

摘要

Bi_2Ti_2O_7 microwave dielectric ceramics were synthesized by a modified sol-gel method using citric acid as metal chelating agent. The thermal decomposition behavior of the as-prepared precursor was characterized by XRD technique. The effects of the amount of citric acid and the molar ratio of bismuth nitrate to tetrabutyl titanate on the crystal structure of Bi_2Ti_2O_7 were also investigated. XRD results showed that well-crystallized Bi_2Ti_2O_7 powders could be synthesized by calcining the precursor at 550°C as the molar ratio of CA to Bi was 1:1. Moreover, non-stoichiometric ratio of Bi to Ti was required to form the pure Bi_2Ti_2O_7 phase. However, Bi_4Ti_3O_(12) and Bi_2Ti_4O_(11) second phases were formed after sintering process. At 1150°C, only the sample doped with 3 wt% Ho~(3+) showed a single pyrochlore structure, which exhibited good microwave dielectric properties with a high ε_r of 115.02, a Ω × /of 1,515 GHz, andar/of 30ppm/°C.