Ferroelectric and photocatalytic properties of Aurivillius phase Ca₂Bi₄Ti₅O₁₈

Aurivillius phase Ca₂Bi₄Ti₅O₁₈ powders with micrometer size were produced by solidstate reaction. X-ray diffraction revealed that the powders had polar orthorhombic structure with space group of B2cb. Ca₂Bi₄Ti₅O₁₈ ceramic exhibited frequency independent dielectric anomaly at 774 °C. The piezoelectric coefficient d33 value of poled Ca₂Bi₄Ti₅O₁₈ pellets was 0.7±0.2 pC/N. Both frequency independent dielectric anomaly and detectable d33 value clearly indicated that Ca₂Bi₄Ti₅O₁₈ is a ferroelectric material with Curie point of 774 ℃. UV–vis absorption spectra revealed that Ca₂Bi₄Ti₅O₁₈ had a direct band gap of 3.2 eV. Photocatalytic activity of the Ca₂Bi₄Ti₅O₁₈ powders was examined by degradation of rhodamine B (RhB) under simulated solar light. 16% of RhB solution was degraded by Ca₂Bi₄Ti₅O₁₈ powders after 4 h UV-vis irradiation. With Ag nanoparticles deposited on the Ca₂Bi₄Ti₅O₁₈ powders surface, 50% of RhB were degraded under the same irradiation condition. The fitted degradation rate constant of Ag decorated Ca₂Bi₄Ti₅O₁₈ was 4 times higher than that of bare Ca₂Bi₄Ti₅O₁₈. This work suggested that the Aurivillius ferroelectric Ca₂Bi₄Ti₅O₁₈ is a promising candidate for photocatalytic applications.