Properties of Sr_(1-x)La_(2x/3)Bi_4Ti_4O_(15) Ferroelectric Ceramics

摘要

Dielectric and ferroelectric properties of La-doped Sr_(1-x)La_(2x/3)Bi_4Ti_4O_(15) (SLBT-x, x = 0.00-0.75) ceramics were investigated. A single phase is achieved up to x = 0.30. The temperature dependence of dielectric permittivity (epsilon) for SLBT-z shows the Curie temperature (T_c) decreases with increasing La content, implying the relaxation of lattice distortion, meanwhile the peak of the epsilon-T curve decreases and broadens, indicating the dispersion of phase transition. The A-site vacancies induced by the substitution of La~(3+) for Sr~(2+) weakened the coupling between the neighboring TiO_6 octahedra and gave rise to the relief of lattice distortion. The broadening of dielectric peak may be attributed to the difference of ionic radii between La~(3+) and Si~(2+) as well as the exchange of La~(3+) at A-site and Bi~(3+) at bismuth oxide layer. The hysteresis loops of SLBT-x shows the La-substitution increased the 2P_r up to 23.1 mu C/cm~2 and lowered E_c down to 79.6 kV/cm. It may be related to the dipole defects induced by higher-valence-doping at A-site.