Preparation of m = 1-2 series natural-superlattice-structured bismuth-layer-structured ferroelectric thin films

C-axis-oriented epitaxial natural-superlattice-structured Bi 2MoO6-Bi3TiNbO9 (BM-BTN) (m = 1-2) and Bi2WO6-Bi3TiNbO9 (BW-BTN) (m = 1-2) films are grown by pulsed-laser deposition (PLD) on SrTiO3 (001) substrates. The c-lattice constant (6.738 nm) of the BM-BTN film is very close to that (6.54 nm) of the superlattice structure of one BM unit cell and two BTN unit cells. The c-lattice constant (2.089 nm) of the BW-BTN film is very close to that (2.07 nm) of the superlattice structure of one BW unit cell and one BTN unit cell. The long-range natural-superlattice-structure of BM and BTN films have been prepared on Pt(111)/TiO2/SiO2/Si substrates by PLD and oxygen postannealing at 650°C. X-ray diffractions clearly show the formation of the long-range superlattice of the 15.5 nm iterative layer, which corresponds to 50 unit cells consisting of (113)-oriented BM and (115)-oriented BTN. These BM BTN thin films exhibit good ferroelectricity with a 2P r of 40 μC/cm2.