Crystal structure and ferroelectric properties of rare-earth substituted BiFeO_3 thin films

摘要

The influence of ion modification using rare-earth cations on crystal structures, along with the insulating and ferroelectric properties of BiFeO_3 (BFO) thin films was investigated. Rare-earth-substituted BFO films with chemical compositions of (Bi_(1.00-x)RE_x)Fe_(1.00)O_3 (x = 0-0.15, RE=La and Nd) were fabricated on (111)Pt/TiO_2/SiO_2/(100)Si substrates using a chemical solution deposition technique. A crystalline phase of rhombohedral BFO was obtained by heat treatment in a N_2 atmosphere at 500℃ for 5 min. The crystal anisotropy and the Curie temperature of BFO were degraded continuously with increasing contents of La~(3+) or Nd~(3+) cations. Ion modification using La~(3+) and Nd~(3+) cations up to x=0.05 lowered the leakage current density of the BFO film at room temperature from approximately 10~(-3) down to 10~(-6) A/cm~2. A polarization (P)-electrical field (E) hysteresis loop measured at 10 K revealed that the intrinsic remanent polarization of La~(3+)- and Nd~(3+)-substituted BFO films with x=0.05 (44 and 51 μC/cm~2, respectively) was smaller than that of a nonsubstituted BFO film (79 μC/cm~2), which is ascribed to the degradation of crystal anisotropy and the Curie temperature of the BFO crystal.