Microscopic Origin of the Giant Ferroelectric Polarization in Tetragonal-likeBiFeO3

Abstract

We report direct experimental evidence for a room-temperature, ∼130 μC/cm(2) ferroelectric polarization from the tetragonal-like BiFeO(3) phase. The physical origin of this remarkable enhancement of ferroelectric polarization has been investigated by a combination of x-ray absorption spectroscopy, scanning transmission electron microscopy, and first principles calculations. A large strain-induced Fe-ion displacement relative to the oxygen octahedra, combined with the contribution of Bi 6s lone pair electrons, is the mechanism driving the large ferroelectric polarization in this tetragonal-like phase.

Tetragonal BiFeO3 on yttria-stabilized zirconia

“…The opposite energy shift observed in main peak and prepeak has been attributed to off-centering of Bi and Fe ions in the O octahedron, leading to a square pyramid (5-fold) coordination. 21,25,33 More obvious evidence can be revealed in XLD spectrum, which is obtained from the intensity difference (I E//a − I E//c ) between the normalized XAS spectra of E//a and E//c. The variation in XLD spectrum is similar to the previous studies on triclinic phases with large c/a ratio, confirming again the large crystal elongation along c-axis for this T-BFO film.…”

“…Both edges exhibit doublet peaks, of which the main peak and prepeak correspond to the higher e g energy level (x 2 -y 2 , 3z 2 -r 2 ) and lower lying t 2g energy level (xy, yz, xz) that are induced by a octahedral crystal field. 25 It is important to note that there is a considerable polarization dependence in the XAS line shape: both peak intensity changes and peak energy shifts have been observed. The relative intensity changes at various peaks mainly arise from "magnetic linear dichroism," [26][27][28][29] while the observed peak energy shifts of several tenths of an eV are mainly attributed "crystal field dichroism."…”

Edge dislocation slows down oxide ion diffusion in doped CeO2 by segregation of charged defects

“…This high density of dislocations makes the study of their effect on the properties of the material of paramount importance. The elastic strain effects in oxides have been extensively studied for transport [9][10][11] , (electro)catalytic activity [12][13][14] and multiferroic properties 15,16 . On the other hand, only a few recent studies directly assessed the potential role of dislocations on the electrical 17,18 , magnetic 19 and chemical 20,21 properties of oxides, probably because of the intrinsic difficulty in studying these extended defects one at a time with high spatial resolution.…”

Engineering ferroelectric tunnel junctions through potential profile shaping

“…6,23,24 Well lattice-matched CCMO layers of about 20 nm thickness were used as bottom electrodes. 25 Recent cross section scanning transmission electron microscopy images evidence a sharp interface between CCMO and BFO with a large c/a ratio for the ultrathin ferroelectric film, which is characteristic of the T-phase.…”