Fig. 2: Atomic displacements in the ladders.
From: Direct visualization of irreducible ferrielectricity in crystals
a Schematic displacements of Fe and Se ions indicated by arrows and amplified in magnitude. Light blue: strong ladder with larger polar bias of Se ions; Dark blue: weak ladder. b, c Color-enhanced HAADF-STEM images of BaFe2Se3 along b-axis and c-axis. The strong and weak ladders are distributed in an alternating order. Scale bar, 1 Å. d, e Superposition of the HAADF image and the polar map of Se atoms along b-axis and Fe atoms along c-axis. The yellow and green arrows there represent the atoms displacements in strong and weak ladders, respectively. Scale bar, 1 nm. f The EELS line scan is across the white line in e. EELS measurements indicate the charge ordering pattern. The averaged Fe L2,3 edge spectrum from neighboring Fe chains is presented. A Fe-L3 peak shift of approximately 0.4 eV between neighboring Fe chain is observed.
