Browsing by Author "Rossell, M. D."

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A Strain-Driven Morphotropic Phase Boundary in BiFeO(3)
(2009-11-13)
Zeches, R. J.
;
Rossell, M. D.
;
Zhang, J. X.
;
Hatt, A. J.
;
He, Q.
Piezoelectric materials, which convert mechanical to electrical energy and vice versa, are typically characterized by the intimate coexistence of two phases across a morphotropic phase boundary. Electrically switching one to the other yields large electromechanical coupling coefficients. Driven by global environmental concerns, there is currently a strong push to discover practical lead-free piezoelectrics for device engineering. Using a combination of epitaxial growth techniques in conjunction with theoretical approaches, we show the formation of a morphotropic phase boundary through epitaxial constraint in lead-free piezoelectric bismuth ferrite (BiFeO(3)) films. Electric field-dependent studies show that a tetragonal-like phase can be reversibly converted into a rhombohedral-like phase, accompanied by measurable displacements of the surface, making this new lead-free system of interest for probe-based data storage and actuator applications.
A Strain-Driven Morphotropic Phase Boundary in BiFeO3
(2009-11-13)
Zeches, R. J.
;
Rossell, M. D.
;
Zhang, J. X.
;
Hatt, A. J.
;
He, Q.
Piezoelectric materials, which convert mechanical to electrical energy and vice versa, are typically characterized by the intimate coexistence of two phases across a morphotropic phase boundary. Electrically switching one to the other yields large electromechanical coupling coefficients. Driven by global environmental concerns, there is currently a strong push to discover practical lead-free piezoelectrics for device engineering. Using a combination of epitaxial growth techniques in conjunction with theoretical approaches, we show the formation of a morphotropic phase boundary through epitaxial constraint in lead-free piezoelectric bismuth ferrite (BiFeO3) films. Electric field-dependent studies show that a tetragonal-like phase can be reversibly converted into a rhombohedral-like phase, accompanied by measurable displacements of the surface, making this new lead-free system of interest for probe-based data storage and actuator applications.
Above-bandgap voltages from ferroelectric photovoltaic devices
(2010-02-01)
Yang, S. Y.
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Seidel, J.
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Byrnes, S. J.
;
Shafer, P.
;
Yang, C. -H.
In conventional solid-state photovoltaics, electron-hole pairs are created by light absorption in a semiconductor and separated by the electric field spaning a micrometre-thick depletion region. The maximum voltage these devices can produce is equal to the semiconductor electronic bandgap. Here, we report the discovery of a fundamentally different mechanism for photovoltaic charge separation, which operates over a distance of 1-2 nm and produces voltages that are significantly higher than the bandgap. The separation happens at previously unobserved nanoscale steps of the electrostatic potential that naturally occur at ferroelectric domain walls in the complex oxide BiFeO(3). Electric-field control over domain structure allows the photovoltaic effect to be reversed in polarity or turned off. This new degree of control, and the high voltages produced, may find application in optoelectronic devices.
Electromechanical Coupling among Edge Dislocations, Domain Walls, and Nanodomains in BiFeO3 Revealed by Unit-Cell-Wise Strain and Polarization Maps
(2013-04-01)
Lubk, A.
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Rossell, M. D.
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Seidel, J.
;
Chu, Y. H.
;
Ramesh, R.
The performance of ferroelectric devices, for example, the ferroelectric field effect transistor, is reduced by the presence of crystal defects such as edge dislocations. For example, it is well-known that edge dislocations play a crucial role in the formation of ferroelectric dead-layers at interfaces and hence finite size effects in ferroelectric thin films. The detailed lattice structure including the relevant electromechanical coupling mechanisms in close vicinity of the edge dislocations is, however, not well-understood, which hampers device optimization. Here, we investigate edge dislocations in ferroelectric BiFeO3 by means of spherical aberration-corrected scanning transmission electron microscopy, a dedicated model-based structure analysis, and phase field simulations. Unit-cell-wise resolved strain and polarization profiles around edge dislocation reveal a wealth of material states including polymorph nanodomains and multiple domain walls characteristically pinned to the dislocation. We locally determine the piezoelectric tensor and identify piezoelectric coupling as the driving force for the observed phenomena, explaining, for example, the orientation of the domain wall with respect to the edge dislocation. Furthermore, an atomic model for the dislocation core is derived.
Evidence of Sharp and Diffuse Domain Walls in BiFeO3 by Means of Unit-Cell-Wise Strain and Polarization Maps Obtained with High Resolution Scanning Transmission Electron Microscopy
(2012-07-25)
Lubk, A.
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Rossell, M. D.
;
Seidel, J.
;
He, Q.
;
Yang, S. Y.
Domain walls (DWs) substantially influence a large number of applications involving ferroelectric materials due to their limited mobility when shifted during polarization switching. The discovery of greatly enhanced conduction at BiFeO3 DWs has highlighted yet another role of DWs as a local material state with unique properties. However, the lack of precise information on the local atomic structure is still hampering microscopical understanding of DW properties. Here, we examine the atomic structure of BiFeO3 109 degrees DWs with pm precision by a combination of high-angle annular dark-field scanning transmission electron microscopy and a dedicated structural analysis. By measuring simultaneously local polarization and strain, we provide direct experimental proof for the straight DW structure predicted by ab initio calculations as well as the recently proposed theory of diffuse DWs, thus resolving a long-standing discrepancy between experimentally measured and theoretically predicted DW mobilities.
Interface control of bulk ferroelectric polarization
(2012-06-19)
Yu, P.
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Luo, W.
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Yi, D.
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Zhang, J. X.
;
Rossell, M. D.
The control of material interfaces at the atomic level has led to novel interfacial properties and functionalities. In particular, the study of polar discontinuities at interfaces between complex oxides lies at the frontier of modern condensed matter research. Here we employ a combination of experimental measurements and theoretical calculations to demonstrate the control of a bulk property, namely ferroelectric polarization, of a heteroepitaxial bilayer by precise atomic-scale interface engineering. More specifically, the control is achieved by exploiting the interfacial valence mismatch to influence the electrostatic potential step across the interface, which manifests itself as the biased-voltage in ferroelectric hysteresis loops and determines the ferroelectric state. A broad study of diverse systems comprising different ferroelectrics and conducting perovskite underlayers extends the generality of this phenomenon.
Interface Ferromagnetism and Orbital Reconstruction in BiFeO(3)-La(0.7)Sr(0.3)MnO(3) Heterostructures
(2010-07-06)
Yu, P.
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Lee, J. -S.
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Okamoto, S.
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Rossell, M. D.
;
Huijben, M.
We report the formation of a novel ferromagnetic state in the antiferromagnet BiFeO(3) at the interface with ferromagnet La(0.7)Sr(0.3)MnO(3). Using x-ray magnetic circular dichroism at Mn and Fe L(2,3) edges, we discovered that the development of this ferromagnetic spin structure is strongly associated with the onset of a significant exchange bias. Our results demonstrate that the magnetic state is directly related to an electronic orbital reconstruction at the interface, which is supported by the linearly polarized x-ray absorption measurement at the oxygen K edge.
Interface Ferromagnetism and Orbital Reconstruction in BiFeO3-La0.7Sr0.3MnO3 Heterostructures
(2010-07-06)
Yu, P.
;
Lee, J. -S.
;
Okamoto, S.
;
Rossell, M. D.
;
Huijben, M.
We report the formation of a novel ferromagnetic state in the antiferromagnet BiFeO3 at the interface with ferromagnet La0.7Sr0.3MnO3. Using x-ray magnetic circular dichroism at Mn and Fe L-2,L-3 edges, we discovered that the development of this ferromagnetic spin structure is strongly associated with the onset of a significant exchange bias. Our results demonstrate that the magnetic state is directly related to an electronic orbital reconstruction at the interface, which is supported by the linearly polarized x-ray absorption measurement at the oxygen K edge.
Microscopic Origin of the Giant Ferroelectric Polarization in Tetragonal-like BiFeO(3)
(2011-09-29)
Zhang, J. X.
;
He, Q.
;
Trassin, M.
;
Luo, W.
;
Yi, D.
We report direct experimental evidence for a room-temperature, similar to 130 mu C/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.
Microscopic Origin of the Giant Ferroelectric Polarization in Tetragonal-like BiFeO3
(2011-09-29)
Zhang, J. X.
;
He, Q.
;
Trassin, M.
;
Luo, W.
;
Yi, D.
We report direct experimental evidence for a room-temperature, similar to 130 mu C/cm(2) ferroelectric polarization from the tetragonal-like BiFeO3 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.