Large remanent polarization of (Bi,Nd)₄Ti₃O ₁₂ epitaxial thin films grown by metalorganic chemical vapor deposition

(104)-oriented Bi₄Ti₃O₁₂, La-substituted Bi₄Ti₃O₁₂[(Bi_3.44La _0.56)Ti₃O₁₂] and Nd-substituted Bi ₄Ti₃O₁₂[(Bi_3.54Nd _0.46)Ti₃O₁₂] films were epitaxially grown on (111)SrRuO₃//(111)SrTiO₃ substrates at 700°C by metalorganic chemical vapor deposition. All deposited films showed strong (104) orientations. The values of the remanent polarization (P_r) and coercive field (E_c) of the (104)-oriented epitaxial (Bi _3.54Nd_0.46)Ti₃O₁₂ thin film were 25 μC/cm² and 135 kV/cm, respectively. This P_r value was larger than that of the (104)-oriented (Bi_3.44La_0.56) Ti₃O₁₂ film: P_r and E_c values of the (Bi_3.44La_0.56)Ti₃O₁₂ were 17 μC/cm² and 145 kV/cm, respectively. These good ferroelectric properties of (Bi_3.54Nd_0.46)Ti₃O₁₂ films can be explained by a large tilting of TiO₆ octahedra induced by the substitution of Nd³⁺, the ionic radius of which is smaller than that of La³⁺. Moreover, this P_r value is almost equal to that of commercially used lead zirconate titanate (PZT) films for nonvolatile ferroelectric random access memory (FeRAM) applications. These (104)-oriented epitaxial (Bi_3.54Nd_0.46)Ti ₃O₁₂ thin films also showed a fatigue-free character. As a result, lead-free Nd-substituted Bi₄Ti₃O₁₂ films with good ferroelectric properties comparable with those of PZT films are useful candidates for FeRAM applications.