Fig. 1: CVD growth of layered 2D Bi2TeO5 single crystals with ferroelectricity.
From: Continuously tunable ferroelectric domain width down to the single-atomic limit in bismuth tellurite
a Optical image of Bi2TeO5 single crystals. b, c AFM topography and corresponding lateral PFM images of single Bi2TeO5 flake. Height profile in b shows a step of 1.2 nm, consistent to the thickness of monolayer Bi2TeO5. d Schematic of Bi2TeO5 crystal structure along a axis. e Top oblique view of layered Bi2TeO5 crystal structure. The blue pyramids correspond to the BiO5 cages. The blue arrows represent the polarization direction of BiO5 cages. The sandwiched Bi-O-Bi sublayers are not shown here for better presentation. f Schematic of Bi2TeO5 crystal structure along c axis. An enlarged image in green rectangle shows the calculated Bi displacements (DBi) and lattice rotation angle (θ). g Atomically resolved HAADF-STEM image of Bi2TeO5 along c axis. Lower left inset: Simulated STEM image of Bi2TeO5. Oxygen columns are invisible due to their weak scattering. h Extracted DBi and θ distribution in g. The error bars correspond to the standard deviation of DBi and θ. i Superposition of Bi3+ displacement vectors with g. For simplicity, only the large displacements of Bi3+ sites (A-rows) are depicted in the image.
