Ferroelectric property of epitaxial Bi₄Ti₃O₁₂ films prepared by metalorganic chemical vapor deposition

The orientation dependence of the ferroelectricity of epitaxially grown Bi₄Ti₃O₁₂ thin films was investigated. The (001)-, (118)-, and (104)-oriented Bi₄Ti₃O₁₂ films were epitaxially grown on (100)_cCaRuO₃//(100)SrTiO₃, (110)_cSrRuO₃//(110)SrTiO₃, and (111)_cSrRuO₃//(111)SrTiO₃ substrates, respectively, by metalorganic chemical vapor deposition. Ferroelectric property with different magnitude was observed for (001)- and (118)-oriented films but for (104)-oriented film due to its large leakage current. The remanent polarization and the coercive field were 1.5 mC/cm² and 15 kV/cm, 16.5 νC/cm² and 132 kV/cm for the (001)- and (118)-oriented thin films, respectively. The spontaneous polarization (P_S) was 4.0 νC/cm² and 27.0 νC/cm² for (001)- and (118)-oriented films, respectively. This was different from the result of SrBi₂Ta₂O₉ in that the ferroelectricity was not observed for (001)-oriented one, and was in good agreement with the estimation from the crystal structure. The estimated P_S values along the c and a axes of Bi₄Ti₃O₁₂ were 4.0 and 48.4 νC/cm², respectively, and agreed well with the reported values for the single crystal. Furthermore, both films showed good fatigue endurance after 7.8 × 10¹⁰ switching cycles measured with 500 kHz rectangular pulses.