Orientation Behavior and Ferro- and Piezoelectric Properties of Bi4-xPrxTi3O12Polycrystalline Films

The significance of orientation control on ferroelectric polarization and electromechanical displacement properties was studied by comparing the difference in growth behavior among Bi 4- x Pr x Ti 3 O 12 films (BPT, x =0.3, 0.5, and 0.7, nominal) deposited on both Pt and Ir sputter-grown bottom electrode layers on Si substrates. BPT films were directly crystallized from precursor solutions and exhibited (111) and (110) preferential orientations on Ir layers but (117) orientation on Pt layers. Because of the tilt angle difference between the major spontaneous polarization P s vector and the above-mentioned axes, BPT films deposited on Ir layers showed a remanent polarization P r that is 10–20% larger than those of the films deposited on Pt layers. Furthermore, P r and Curie temperature T c monotonically decreased with increasing x . This corresponds to the fact that substitution of Pr 3+ for Bi 3+ may not improve the ferroelectric polarization properties. The values of longitudinal electromechanical displacement in BPT films deposited on Ir layers were measured by atomic force microscopy (AFM). The uniform response within the film and the top electrode was a direct consequence of the uniform growth of the films. A maximum displacement was measured at x =0.3 and this qualitatively agrees with the finding that the product ε r P s can attain a maximum value with a positive value of x by considering the observed behavior that both P sat and T c monotonically decrease with increasing x .