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Ferroelectric-like metallic state in electron doped BaTiO3.

Fujioka J, Doi A, Okuyama D, Morikawa D, Arima T, Okada KN, Kaneko Y, Fukuda T, Uchiyama H, Ishikawa D, Baron AQ, Kato K, Takata M, Tokura Y - Sci Rep (2015)

Bottom Line: We report that a ferroelectric-like metallic state with reduced anisotropy of polarization is created by the doping of conduction electrons into BaTiO3, on the bases of x-ray/electron diffraction and infrared spectroscopic experiments.The crystal structure is heterogeneous in nanometer-scale, as enabled by the reduced polarization anisotropy.The enhanced infrared intensity of soft phonon along with the resistivity reduction suggests the presence of unusual electron-phonon coupling, which may be responsible for the emergent ferroelectric structure compatible with metallic state.

View Article: PubMed Central - PubMed

Affiliation: Department of Applied Physics and Quantum-Phase Electronics Center (QPEC), University of Tokyo, Hongo, Tokyo 113-8656, Japan.

ABSTRACT
We report that a ferroelectric-like metallic state with reduced anisotropy of polarization is created by the doping of conduction electrons into BaTiO3, on the bases of x-ray/electron diffraction and infrared spectroscopic experiments. The crystal structure is heterogeneous in nanometer-scale, as enabled by the reduced polarization anisotropy. The enhanced infrared intensity of soft phonon along with the resistivity reduction suggests the presence of unusual electron-phonon coupling, which may be responsible for the emergent ferroelectric structure compatible with metallic state.

No MeSH data available.


(a) Inelastic x-ray scattering spectra taken at 350 K. The blue, red and green lines denote the fitted results for transverse acoustic mode, soft mode and Last mode, respectively. The mode around 28 meV denoted by purple lines may be multi-phonon band or infrared inactive optical phonon. (b) Energy dispersion of phonons. The energies at q = 0 (open symbols) are determined by the optical conductivity spectra. (c) The inelastic scattering spectra at various temperatures at Q = (0.08 0.08 5). The peak-like structure below 3 meV is an artifact due to the Bose correction.
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f5: (a) Inelastic x-ray scattering spectra taken at 350 K. The blue, red and green lines denote the fitted results for transverse acoustic mode, soft mode and Last mode, respectively. The mode around 28 meV denoted by purple lines may be multi-phonon band or infrared inactive optical phonon. (b) Energy dispersion of phonons. The energies at q = 0 (open symbols) are determined by the optical conductivity spectra. (c) The inelastic scattering spectra at various temperatures at Q = (0.08 0.08 5). The peak-like structure below 3 meV is an artifact due to the Bose correction.

Mentions: This scenario is further supported by the nonresonant inelastic x-ray scattering (IXS) spectra. Figure 5(a) displays the IXS spectra at various reduced wave vectors (q) along (110) in the paraelectric phase taken at 350 K. Here, phonons with polarization parallel to [001] direction, that is, the transverse phonon is discernible due to the nearly orthogonal relation between the polarization vector and q. The IXS spectrum at q = 0.08 shows two intense peaks at 5 and 23 meV due to the transverse acoustic (TA) phonon and Last mode, respectively. Moreover, the soft mode manifests itself as a broad continuum with significantly reduced scattering intensity around 10 meV. The mode around 28 meV with broad peak width may be attributed to the multiphonon band or infrared inactive optical phonon. We note that a similar intensity profiles of phonons are observed in the perovskite-type ferroelectrics Sr1–xBaxMnO328, supporting our mode assignment. To derive the energy of each mode, we assumed the damped harmonic oscillators to reproduce spectra. The energy dispersion of each mode is summarized in Fig. 5(b). The energy of soft mode appears to decrease with approaching Γ-point as often seen in various perovskite-type ferroelectrics. Figure 5(c) displays the temperature dependence of IXS spectra at (0.08 0.08 5). The IXS intensity exhibits minimal temperature dependence around 10 meV, in contrast with the large temperature dependence of infrared spectra. In general, the scattering intensity of nonresonant IXS is governed by that of phonons, while the intensity of infrared spectra is sensitive to both electronic excitations and infrared active optical phonons293031. Therefore, the enhanced infrared intensity of soft phonon suggests the presence of electronic excitation, which is strongly coupled to the soft phonon.


Ferroelectric-like metallic state in electron doped BaTiO3.

Fujioka J, Doi A, Okuyama D, Morikawa D, Arima T, Okada KN, Kaneko Y, Fukuda T, Uchiyama H, Ishikawa D, Baron AQ, Kato K, Takata M, Tokura Y - Sci Rep (2015)

(a) Inelastic x-ray scattering spectra taken at 350 K. The blue, red and green lines denote the fitted results for transverse acoustic mode, soft mode and Last mode, respectively. The mode around 28 meV denoted by purple lines may be multi-phonon band or infrared inactive optical phonon. (b) Energy dispersion of phonons. The energies at q = 0 (open symbols) are determined by the optical conductivity spectra. (c) The inelastic scattering spectra at various temperatures at Q = (0.08 0.08 5). The peak-like structure below 3 meV is an artifact due to the Bose correction.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4542543&req=5

f5: (a) Inelastic x-ray scattering spectra taken at 350 K. The blue, red and green lines denote the fitted results for transverse acoustic mode, soft mode and Last mode, respectively. The mode around 28 meV denoted by purple lines may be multi-phonon band or infrared inactive optical phonon. (b) Energy dispersion of phonons. The energies at q = 0 (open symbols) are determined by the optical conductivity spectra. (c) The inelastic scattering spectra at various temperatures at Q = (0.08 0.08 5). The peak-like structure below 3 meV is an artifact due to the Bose correction.
Mentions: This scenario is further supported by the nonresonant inelastic x-ray scattering (IXS) spectra. Figure 5(a) displays the IXS spectra at various reduced wave vectors (q) along (110) in the paraelectric phase taken at 350 K. Here, phonons with polarization parallel to [001] direction, that is, the transverse phonon is discernible due to the nearly orthogonal relation between the polarization vector and q. The IXS spectrum at q = 0.08 shows two intense peaks at 5 and 23 meV due to the transverse acoustic (TA) phonon and Last mode, respectively. Moreover, the soft mode manifests itself as a broad continuum with significantly reduced scattering intensity around 10 meV. The mode around 28 meV with broad peak width may be attributed to the multiphonon band or infrared inactive optical phonon. We note that a similar intensity profiles of phonons are observed in the perovskite-type ferroelectrics Sr1–xBaxMnO328, supporting our mode assignment. To derive the energy of each mode, we assumed the damped harmonic oscillators to reproduce spectra. The energy dispersion of each mode is summarized in Fig. 5(b). The energy of soft mode appears to decrease with approaching Γ-point as often seen in various perovskite-type ferroelectrics. Figure 5(c) displays the temperature dependence of IXS spectra at (0.08 0.08 5). The IXS intensity exhibits minimal temperature dependence around 10 meV, in contrast with the large temperature dependence of infrared spectra. In general, the scattering intensity of nonresonant IXS is governed by that of phonons, while the intensity of infrared spectra is sensitive to both electronic excitations and infrared active optical phonons293031. Therefore, the enhanced infrared intensity of soft phonon suggests the presence of electronic excitation, which is strongly coupled to the soft phonon.

Bottom Line: We report that a ferroelectric-like metallic state with reduced anisotropy of polarization is created by the doping of conduction electrons into BaTiO3, on the bases of x-ray/electron diffraction and infrared spectroscopic experiments.The crystal structure is heterogeneous in nanometer-scale, as enabled by the reduced polarization anisotropy.The enhanced infrared intensity of soft phonon along with the resistivity reduction suggests the presence of unusual electron-phonon coupling, which may be responsible for the emergent ferroelectric structure compatible with metallic state.

View Article: PubMed Central - PubMed

Affiliation: Department of Applied Physics and Quantum-Phase Electronics Center (QPEC), University of Tokyo, Hongo, Tokyo 113-8656, Japan.

ABSTRACT
We report that a ferroelectric-like metallic state with reduced anisotropy of polarization is created by the doping of conduction electrons into BaTiO3, on the bases of x-ray/electron diffraction and infrared spectroscopic experiments. The crystal structure is heterogeneous in nanometer-scale, as enabled by the reduced polarization anisotropy. The enhanced infrared intensity of soft phonon along with the resistivity reduction suggests the presence of unusual electron-phonon coupling, which may be responsible for the emergent ferroelectric structure compatible with metallic state.

No MeSH data available.