Ferroelectric properties of sol-gel prepared La- and Nd-substituted, and Nb-co-substituted bismuth titanate using polymeric additives

La- or Nd-substituted bismuth titanate (BLT or BNT) and Nb-cosubstituted bismuth titanate (Nb-BLT or Nb-BNT) thin films were prepared in the presence of nonionic surfactants, poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide) (EOxPOyEOx) triblock copolymers, added as additives to the sol solution. For Nb-BLT films prepared with EO106PO70EO106, the (200) orientation relative to (117) was dominant as compared with Nb-BLT films produced without surfactant or with EO20PO70EO20, and the remanent polarization (Pr) of the Nb-BLT film was 22 μC/cm2, which was superior to 10 and 15 μC/cm2 of Nb-BLT films prepared without surfactant or with EO20PO70EO20. The additional Nb cosubstitution in BLT and BNT affected particle orientation in the films and resulted in higher ferroelectricity than those of the BLT and BNT films. The Nb-BNT/EO106PO70EO106 film showed the best ferroelectric properties; its remanent polarization was 30 μC/cm2 and the polarization (P*–P˄) shows no significant change up to 8 × 108 switching cycles.