Effect of Lithium Fluoride on the Dielectric Properties of Barium Titanate

Abstract

The purpose of this study was to investigate the dielectric properties of BaTiO₃ (BTO) ceramics sintered with the aid of lithium fluoride. BTO with various ratios BaO/TiO₂ (0.97, 1.00, 1.03) was synthesized by calcination of BaCO₃ and TiO₂ at 1100 °C. The different BTO powders were mixed with 1, 2 or 3 wt.% of LiF and then wet-ground in ethanol. The mixtures were cold-pressed to pellets with “latex” as a binder. The disks were sintered in free-air or sealed tube at 750, 850, 950 or 1100 °C, respectively, for 2 or 8 h. The obtained ceramics were checked by X-ray diffraction, scanning electron microscopy, differential thermal analyses and Auger microprobe. Dielectric measurements were carried out under vacuum at 1 kHz in the temperature range 180–500 K. Chemical analyses were performed and lithium and fluorine losses were calculated. Results show that the addition of LiF to BTO lowered both the sintering temperature and the ferroelectric Curie temperature T _C. Most ceramics exhibited a broad maximum of the permittivity ${\varepsilon_{\rm r}^{\prime}}$ and small dielectric losses tan${\delta}$ at T _C. The best dielectric characteristics were observed from BTO (1.03) ceramic sintered with 2 wt.% of LiF at 950 °C for 2 h and then reheated at 1200 °C for 2 h in sealed tube: T _C = 248 K, ${\varepsilon_{\rm r}^{\prime}}$ at T _C = 8650, tan${\delta}$ at T _C = 6 × 10⁻³. The majority of prepared ceramics could be of interest in the manufacture of Z5U multilayer capacitors at low factory cost.