Properties of Sr1-xLa2x/3Bi4Ti4O15 ferroelectric ceramics

Dielectric and ferroelectric properties of La-doped Sr1-xLa2x/3Bi4Ti4O15 (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-x 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 La3+ for Sr2+ weakened the coupling between the neighboring TiO6 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 La3+ and Sr2+ as well as the exchange of La3+ at A-site and Bi3+ 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.