Bi-based ferroelectric thin films with enhanced polarization by rare-earth modification

Thin films of Bi-based perovskite ferroelectrics BiFeO₃ is recently recognized as strong candidates for alternatives to toxic Pb-based ferroelectrics such as conventional Pb(Zr,Ti)O₃. Authors fabricated BiFeO₃ thin films with excellent performance of ferroelectric polarization by ion modification based on sol-gel technique. Some rare-earth ions, such as La³⁺ or Nd³⁺, could be substituted for Bi³⁺ ion in BFO crystal in order to reduce ionic defects in crystal lattices. Electrical resistivity of BiFeO₃ films were improved by ion modification of rare-earth elements, as well as other Bi-based ferroelectric films like Bi₄Ti₃O₁₂. Although crystal anisotropy and phase-transition temperature (Curie temperature) of these materials are generally reduced by the ion modification, it yield fully-saturated polarization (P) - electrical field (E) property to produce enhanced remanent polarization of approximately 50 μC/cm² comparable or superior to conventional Pb(Zr,Ti)O₃ films. We concluded that the ion modification using rare-earth elements could suppress the ionic defects that caused electrical conduction in BiFeO₃ films.