Enhanced Ferroelectric Polarization in Laser-ablated Bi4Ti3O12 Thin Films by Controlling Preferred Orientation

Polycrystalline Bi_4Ti_3O_（12） thin films with various fractions of a-axis, c-axis and random orientations have been grown on Pt（111）/Ti/Si O_2/Si substrates by laser-ablation under different kinetic growth conditions. The relationship between the structure and ferroelectric property of the films was investigated, so as to explore the possibility of enhancing ferroelectric polarization by controlling the preferred orientation. The structural characterization indicated that the large growth rate and high oxygen background pressure were both favorable for the growth of non-c-axis oriented grains in the Bi_4Ti_3O_（12） thin films. The films with high fractions of a-axis and random orientations, i e, f（a-sxis） = 28.3% and f（random） = 69.6%, could be obtained at the deposition temperature of 973 K, oxygen partial pressure of 15 Pa and laser fluence of 4.6 J/cm^2, respectively. It was also noted that the variation of ferroelectric polarization was in accordance with the evolution non-c-axis orientation. A large value of remanent polarization（2 Pr = 35.5 μC/cm^2） was obtained for the Bi_4Ti_3O_（12） thin films with significant non-c-axis orientation, even higher than that of rare-earth-doped Bi_4Ti_3O_（12） films.