Mechanism of polarization enhancement in la-doped Bi4Ti3O12 films -: art. no. 032907

Bi4-xLaxTi3O12 (La-doped BIT, x=0-0.6) thin films prepared by metalorganic decomposition method, were studied using x-ray diffraction (XRD), polarization hysteresis and Raman scattering techniques. The XRD and polarization studies showed that La substitution reduces structural distortion, relaxes internal strain and enhances polarization, while the Raman data indicate that the added La occupies mainly at A sites in the BIT films. Raman modes also indicate an increase in TiO6 symmetry, internal strain relaxation, lower Ti-O hybridization, and decrease in polarization along the a axis. Further, the polarization in the highly c-oriented BIT films significantly increases with the added La, hence a polarization tilt towards the c axis is implied. The higher polarization observed can be attributed, therefore, to microscopic changes involving decreased distortion in the TiO6 octahedra and a polarization tilt towards the c axis, caused by doping with the electronically less active ion (e.g., La, Y) onto the A sites in the BIT structure. This understanding is important to the commercialization of high-density ferroelectric random access memories. (C) 2005 American Institute of Physics.