A study on the properties of (Bi, La)4Ti3O12- Sr(Bi, La)4Ti4O15 intergrowth ferroelectrics

Lanthanum_doped intergrowth ferroelectrics: (Bi,La)4Ti3O 12-Sr(Bi,La)4Ti4O15 (SrBi8-xLaxTi7O27) (x＝0.00, 0.25, 0.50, 0.75, 1.00, 1.25, 1.50) ceramic samples have been prepared by solid_state reaction m ethod. Their structure was analyzed by x_ray diffraction, and their dielectricit y and ferroelectricity were measured. It is found that La doping does not change the crystal structure of Bi4Ti3O12-SrBi4Ti4O15. The coerciv e field (EC) of SrBi8-xLaxTi7O2 7 increases slightly and the remnant polarization (2Pr) increases at first, then decreases with th e increas e of La content. The 2Pr reaches a maximum value of 25.6 μC·cm-2, whe n x is 0.50. The 2Pr increases nearly 60%, but the EC incr eases only about 10%, compared with those of SrBi8Ti7O27. Their temperatures of phase t ransition (TC) decrease with La doping. The TC of SrBi7.5La0.50Ti7O27 is 556 ℃ and shows good thermal stability. As x becomes 1.50, the SrBi7.5La0.50Ti7O27 exhibits a characteristic of relaxor ferroelectrics.