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Acta Materialia 82 (2015) 356-368

Nanodomains and nanometre-scale disorder in multiferroic bismuth ferrite single crystals

by Chun-Lin Jia, Lei Jin, Dawei Wang, Shao-Bo Mi, Marin Alexe, Dietrich Hesse, Helena Reichlova, Xavi Marti, Laurent Bellaiche, and Knut Urban

ER-C scientist together with partners from the Xi’an Jiaotong University (PRC), the Max Planck Institute of Microstructure Physics in Halle, the Institute of Physics in Prague (Czech Republic) and the University of Arkansas in Fayetteville (US) report on an investigation of state-of-the-art flux-grown multiferroic bismuth ferrite (BiFeO3; BFO) single crystals by transmission electron microscopy and electron diffraction. The crystals were pre-characterised by piezoresponse force microscopy, electrical resistance and superconducting quantum interference device magnetisation measurements. The structurally highly perfect crystals show a ferroelectric stripe domain structure characterised by a domain width of 55 nm. Inside these domains an additional contiguous nanodomain substructure occurs, consisting of 180° related domains, giving rise to satellite reflections at {1/2 1/2 1/2}-type positions along ‹110› directions in the electron diffraction pattern corresponding to a characteristic length in real space of 15.5 nm.

Furthermore, for the first time atomic-resolution results on the short-range order by aberration-corrected transmission electron microscopy in which all atoms including oxygen are imaged directly are presented. By measuring the Fe–O–Fe atom topology, bond angles and atomic distances the electrical dipole moment as well as the magnitude of the magnetic moment on the unit-cell level are derived. The results evidence substantial atomic- to nano-scale disorder. Both the nanodomain substructure as well as the disorder should affect the subtle magnetoelectric interactions in this material and thereby impede the formation of long-range cycloidal spin ordering which up to now was considered an intrinsic feature of the magnetic properties of BiFeO3 single crystals. By Monte Carlo simulations on the basis of a state-of-the-art effective Hamiltonian certain aspects of the phase formation behaviour in the BFO system forming the background of single-crystal growth are scrutinised. Results demonstrate a very sluggish phase evolution behaviour, which should make it invariably difficult to obtain structurally fully equilibrated single crystals.

Further reading:

Chun-Lin Jia, Lei Jin, Dawei Wang, Shao-Bo Mi, Marin Alexe, Dietrich Hesse, Helena Reichlova, Xavi Marti, Laurent Bellaiche, and Knut Urban: Nanodomains and nanometre-scale disorder i
n multiferroic bismuth ferrite single crystals, Acta Materialia 82 (2015) 356-368.

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