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Revealing the flexoelectricity in the mixed-phase regions of epitaxial BiFeO3 thin films.

Cheng CE, Liu HJ, Dinelli F, Chen YC, Chang CS, Chien FS, Chu YH - Sci Rep (2015)

Bottom Line: Understanding the elastic response on the nanoscale phase boundaries of multiferroics is an essential issue in order to explain their exotic behaviour.Significantly, the correlation between elastic modulation and piezoresponse across the mixed-phase regions manifests that the flexoelectric effect results in the enhancement of the piezoresponse at the phase boundaries and in the MI regions.This accounts for the giant electromechanical effect in strained mixed-phase BiFeO3 films.

View Article: PubMed Central - PubMed

Affiliation: 1] Department of Photonics and Institute of Electro-Optical Engineering, National Chiao Tung University, Hsinchu, 30010, Taiwan [2] Department of Applied Physics, Tunghai University, Taichung, 40704, Taiwan.

ABSTRACT
Understanding the elastic response on the nanoscale phase boundaries of multiferroics is an essential issue in order to explain their exotic behaviour. Mixed-phase BiFeO3 films, epitaxially grown on LaAlO3 (001) substrates, have been investigated by means of scanning probe microscopy to characterize the elastic and piezoelectric responses in the mixed-phase region of rhombohedral-like monoclinic (MI) and tilted tetragonal-like monoclinic (MII,tilt) phases. Ultrasonic force microscopy reveal that the regions with low/high stiffness values topologically coincide with the MI/MII,tilt phases. X-ray diffraction strain analysis confirms that the MI phase is more compliant than the MII,tilt one. Significantly, the correlation between elastic modulation and piezoresponse across the mixed-phase regions manifests that the flexoelectric effect results in the enhancement of the piezoresponse at the phase boundaries and in the MI regions. This accounts for the giant electromechanical effect in strained mixed-phase BiFeO3 films.

No MeSH data available.


Related in: MedlinePlus

RSM of BFO thin films around the direction LAO (001) in order to show the diffraction peaks of the R, MI (diamond), MII (circle) and MII,tilt (square) phases.
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f3: RSM of BFO thin films around the direction LAO (001) in order to show the diffraction peaks of the R, MI (diamond), MII (circle) and MII,tilt (square) phases.

Mentions: To verify the UFM findings, room-temperature RSM has been then performed. RSM data of the partially-relaxed BFO thin film on LaAlO3 (001) substrate (LAO) include the diffraction peaks of the MI, MII and MII,tilt phases (Fig. 3). The MI phase has a lattice constant in c axis of 4.16 Å, whereas MII and MII,tilt phases have an identical lattice constant (c = 4.65 Å). Both the MI and MII,tilt phases have an off-normal c-axis orientation, where the MI phase has a tilted angle of 2.8° and the MII,tilt phase of 1.6°. The tilted angle values are well consistent with the results obtained from the AFM topography. Fig. 4 shows the diffraction profiles across the MII,tilt peaks in Qx and Qz, and the MI peak in the longitudinal direction. The peaks can be fitted by Gaussian functions; the full widths at half maximum (FWHM) of those peaks are listed in Table I. The FWHM of the MI peak in Qx/Qz is the x/z component of the FWHM in the longitudinal direction. Obviously, the peak of the MI phase is wider than that of the MII,tilt phase by 58% in Qx and 33% in Qz. The wider peak in the Qx reflects the misorientation of the c axis, while the wider peak in the Qz reflects a larger distortion in the c-axis spacing and/or a smaller grain size in the c axis. From the cross-section TEM image, reported in the supplementary materials by Liu et al.8, the MI and MII,tilt phases have a well epitaxial relationship with the MII phase and the substrate. The grains of all phases extend from the surface to the substrate, so those phases have the same grain size along the out-of-plane direction. Therefore, the broadness in Qz of MI phase is merely attributed to the distortion of the c-axis spacing instead of a grain size effect. The larger misorientation and spacing distortion of the c-axis of the MI phase depict its more ambiguous lattice structure, which implies that the stiffness in the MI phase is lower than that in MII,tilt.


Revealing the flexoelectricity in the mixed-phase regions of epitaxial BiFeO3 thin films.

Cheng CE, Liu HJ, Dinelli F, Chen YC, Chang CS, Chien FS, Chu YH - Sci Rep (2015)

RSM of BFO thin films around the direction LAO (001) in order to show the diffraction peaks of the R, MI (diamond), MII (circle) and MII,tilt (square) phases.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4308693&req=5

f3: RSM of BFO thin films around the direction LAO (001) in order to show the diffraction peaks of the R, MI (diamond), MII (circle) and MII,tilt (square) phases.
Mentions: To verify the UFM findings, room-temperature RSM has been then performed. RSM data of the partially-relaxed BFO thin film on LaAlO3 (001) substrate (LAO) include the diffraction peaks of the MI, MII and MII,tilt phases (Fig. 3). The MI phase has a lattice constant in c axis of 4.16 Å, whereas MII and MII,tilt phases have an identical lattice constant (c = 4.65 Å). Both the MI and MII,tilt phases have an off-normal c-axis orientation, where the MI phase has a tilted angle of 2.8° and the MII,tilt phase of 1.6°. The tilted angle values are well consistent with the results obtained from the AFM topography. Fig. 4 shows the diffraction profiles across the MII,tilt peaks in Qx and Qz, and the MI peak in the longitudinal direction. The peaks can be fitted by Gaussian functions; the full widths at half maximum (FWHM) of those peaks are listed in Table I. The FWHM of the MI peak in Qx/Qz is the x/z component of the FWHM in the longitudinal direction. Obviously, the peak of the MI phase is wider than that of the MII,tilt phase by 58% in Qx and 33% in Qz. The wider peak in the Qx reflects the misorientation of the c axis, while the wider peak in the Qz reflects a larger distortion in the c-axis spacing and/or a smaller grain size in the c axis. From the cross-section TEM image, reported in the supplementary materials by Liu et al.8, the MI and MII,tilt phases have a well epitaxial relationship with the MII phase and the substrate. The grains of all phases extend from the surface to the substrate, so those phases have the same grain size along the out-of-plane direction. Therefore, the broadness in Qz of MI phase is merely attributed to the distortion of the c-axis spacing instead of a grain size effect. The larger misorientation and spacing distortion of the c-axis of the MI phase depict its more ambiguous lattice structure, which implies that the stiffness in the MI phase is lower than that in MII,tilt.

Bottom Line: Understanding the elastic response on the nanoscale phase boundaries of multiferroics is an essential issue in order to explain their exotic behaviour.Significantly, the correlation between elastic modulation and piezoresponse across the mixed-phase regions manifests that the flexoelectric effect results in the enhancement of the piezoresponse at the phase boundaries and in the MI regions.This accounts for the giant electromechanical effect in strained mixed-phase BiFeO3 films.

View Article: PubMed Central - PubMed

Affiliation: 1] Department of Photonics and Institute of Electro-Optical Engineering, National Chiao Tung University, Hsinchu, 30010, Taiwan [2] Department of Applied Physics, Tunghai University, Taichung, 40704, Taiwan.

ABSTRACT
Understanding the elastic response on the nanoscale phase boundaries of multiferroics is an essential issue in order to explain their exotic behaviour. Mixed-phase BiFeO3 films, epitaxially grown on LaAlO3 (001) substrates, have been investigated by means of scanning probe microscopy to characterize the elastic and piezoelectric responses in the mixed-phase region of rhombohedral-like monoclinic (MI) and tilted tetragonal-like monoclinic (MII,tilt) phases. Ultrasonic force microscopy reveal that the regions with low/high stiffness values topologically coincide with the MI/MII,tilt phases. X-ray diffraction strain analysis confirms that the MI phase is more compliant than the MII,tilt one. Significantly, the correlation between elastic modulation and piezoresponse across the mixed-phase regions manifests that the flexoelectric effect results in the enhancement of the piezoresponse at the phase boundaries and in the MI regions. This accounts for the giant electromechanical effect in strained mixed-phase BiFeO3 films.

No MeSH data available.


Related in: MedlinePlus