Study on Properties of Lanthanum Doped SrBi4Ti4O15and Sr2Bi4Ti5O18Ferroelectric Ceramics

SrBi 4- x La x Ti 4 O 15 and Sr 2 Bi 4- x La x Ti 5 O 18 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 SrBi 4 Ti 4 O 15 and Sr 2 Bi 4 Ti 5 O 18 . Their coercive field ( E c ) decreases with the increase of La doping content. The remnant polarization (2 P r ) of SrBi 4- x La x Ti 4 O 15 increases at first, then decreases with La doping. The 2 P r reaches a maximum value of 24.2 µC·cm -2 , when x is 0.25. The E c of SrBi 3.75 La 0.25 Ti 4 O 15 is 60.8 kV·cm -1 . The 2 P r increases by about 50% and the E c decreases by nearly 25%, compared with those of SrBi 4 Ti 4 O 15 . Obviously, the ferroelectricity of SrBi 4 Ti 4 O 15 is improved by La doping. The 2 P r and E c of Sr 2 Bi 4- x La x Ti 5 O 18 decrease monotonically with La doping, and its ferroelectricity is not improved. Their temperatures of phase transition decrease with La doping. The T c of SrBi 3.75 La 0.25 Ti 4 O 15 is 451°C.