Study on properties of lanthanum doped SrBi4Ti4O15 and Sr2Bi4Ti5O18 ferroelectric ceramics

SrBi4-xLaxTi4O15 and Sr2Bi4-xLaxTi5O18 ceramic samples with different lanthanum content, in which x is 0.00, 0.10, 0.25, 0.50, 0.75, 1.00, have been prepared by the solid-state reaction method. It is found that La doping does not change the crystal structures of SrBi4Ti4O15 and Sr2Bi4Ti5O18. Their coercive field (E-c) decreases with the increase of La doping content. The remnant polarization (2P(r)) of SrBi4-xLaxTi4O15 increases at first, then decreases with La doping. The 2P(r) reaches a maximum value of 24.2 muC(.)cm(-2), when x is 0.25. The E-c of SrBi3.75La0.25Ti4O15 is 60.8 kV(.)cm(-1). The 2P(r) increases by about 50% and the E-c decreases by nearly 25%, compared with those of SrBi4Ti4O15. Obviously, the ferroelectricity of SrBi4Ti4O15 is improved by La doping. The 2P(r) and E-c of Sr2Bi4-xLaxTi5O18 decrease monotonically with La doping, and its ferroelectricity is not improved. Their temperatures of phase transition decrease with La doping. The T-c of SrBi3.75La0.25Ti4O15 is 451degreesC.