Formation of anisotropic grains and modified ferroelectric properties in Cr‐doped Bi₅FeTi₃O₁₅ thin films

Abstract

Aurivillius phase Bi 5 Cr x Fe 1−x Ti 3 O 15 (0≤ x ≤1) thin films are prepared by the chemical solution deposition method, and the effect of Cr content on the microstructure, ferroelectric property, and electric transport behavior of Bi 5 Cr x Fe 1−x Ti 3 O 15 films is investigated. X-ray diffraction analysis shows that all of Bi 5 Cr x Fe 1−x Ti 3 O 15 films are complete solid solution and maintain the Aurivillius structure. The replacement of Fe 3+ with smaller Cr 3+ decreases anisotropy and lattice aspect ratio in a-b plane, which is minimized at the composition of Bi 5 Cr 0.5 Fe 0.5 Ti 3 O 15 . This changes the grain shape from sphere to plate, and Bi 5 Cr 0.5 Fe 0.5 Ti 3 O 15 film consists of only plate-like grains. Cr doping increases saturated polarization (P m ) and decreases coercive field (E c ). Cr doping increases P m of Bi 5 Cr x Fe 1−x Ti 3 O 15 film to 35 μC/cm 2 , but decreases E c down to 125 kV/cm. A decrease in the lattice aspect ratio of a-b plane promotes the alignment of ferroelectric dipoles under electric field. The frequency-dependent dielectric property and the leakage current show that the plate-like grains of Cr-rich Bi 5 Cr x Fe 1−x Ti 3 O 15 films suppress the transport of carriers from grains to grains and prevents a dramatic leakage current increase. The results of this study provide a design rule to control the ferroelectricity of Aurivillius phase Bi 5 Cr x Fe 1−x Ti 3 O 15 thin films by modifying the composition and lattice aspect ratio.