Synthesis and characteristics of nature-superlattice-structured Bi3TiNbO9-Bi4Ti3O12 ferroelectric thin films by MOD

Natural-superlattice-structured ferroelectric thin films, Bi3TiNbO9-Bi4Ti3O12 (BTN-BIT), have been synthesized on Pt/Ti/SiO2/Si by metal organic decomposition (MOD) using BTN-BIT (1 mol:1 mol) solution. BTN-BIT films show natural-superlattice peaks below 2θ = 20° in X-ray diffraction patterns, which indicate that the BTN-BIT films annealed at 700-800 °C in O2 ambient are consisted of iteration of two unit cells of Bi3TiNbO9 and one unit cell of Bi4Ti3O12. As the annealing temperature increases from 600 to 750 °C, uniform and crack-free films, better crystallinity and ferroelectric properties can be obtained, but the pyrochlore phase in BTN-BIT films annealed over 800 °C would impair the ferroelectric properties. With the increase of O2 flow rate from 0.5 to 1.5 L/min, both remanent polarization Pr and coercive electric field EC increase, which are mainly attributed to reduction of the vacanvies of Bi and oxide ions in the films. Natural-superlattice-structured BTN-BIT thin films having 2-1 superlattice annealed at 750 °C in O2 ambient with a flow rate of 1.5 L/min exhibit superior ferroelectric properties of Pr = 23.5 μC/cm2 and EC = 135 kV/cm.