Polarization comparison of Pb(Zr,Ti)O₃ and Bi₄Ti ₃O₁₂-based ferroelectrics

The spontaneous polarization (P_s) values of Pb(Zr,Ti)O ₃ (PZT) and Bi₄Ti₃O₁₂-based ferroelectrics were compared based on data obtained from epitaxially-grown films. These two materials are the most promising candidates for use in ferroelectric random access memory (FeRAM). The P_s of tetragonal Pb(Zr_0.35Ti_0.65)O₃ films was estimated to be about 90 μC/cm² based on data from perfectly (0 0 1)-oriented, polar-axis-oriented films. On the other hand, the P_s value of (Bi_3.5Nd_0.5)Ti₃O₁₂ was estimated to be 56-58 μC/cm² based on data from (1 0 0)/(0 1 0)-, (1 1 0)-, and (1 0 4)/(0 1 4)-oriented epitaxial films. This value is the largest yet reported for bismuth layer-structured ferroelectrics. For both systems, the P_s value generally increased with increasing Curie temperature (T_c). However, it decreased when the T_c became very high and approached the values for PbTiO₃ and Bi₄Ti ₃O₁₂. This decrease is attributed to pinning of the domain motion in the bulk. On the other hand, the obtained one-axis film, which is essential to diminish the cell-to-cell property distribution, had a (1 0 0)/(0 0 1) and (1 1 1) orientations for Pb(Zr_0.35Ti_0.65)O ₃ films, or a (0 0 1) orientation for (Bi_3.5Nb _0.5)Ti₃O₁₂ films. Based on our findings, we expect the maximum remanent polarization (P_r) values to be almost the same for both materials.