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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.


Structural phase diagram and schematic view of the macroscopic polarization in electron doped BaTiO3.C, T, O, R and M represent cubic, tetragonal, orthorhombic, rhombohedral and monoclinic, respectively. Arrows denote the direction of macroscopic electric polarization (P). P is pointing toward ,  and  in tetragonal, orthorhombic and rhombohedral phase, respectively, while that in the ‘monoclinic’ phase does to a certain direction in-between  and  direction within  plane. The shaded plane indicates  plane.
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f1: Structural phase diagram and schematic view of the macroscopic polarization in electron doped BaTiO3.C, T, O, R and M represent cubic, tetragonal, orthorhombic, rhombohedral and monoclinic, respectively. Arrows denote the direction of macroscopic electric polarization (P). P is pointing toward , and in tetragonal, orthorhombic and rhombohedral phase, respectively, while that in the ‘monoclinic’ phase does to a certain direction in-between and direction within plane. The shaded plane indicates plane.

Mentions: The perovskite BaTiO3 is a prototypical ferroelectric, which is currently utilized in a variety of electronic devices including capacitors, thermistors and nonlinear optical crystals. It shows versatile thermally-induced ferroelectric phases with the macroscopic electric polarization parallel to , and axes as characterized by tetragonal, orthorhombic and rhombohetral crystallographic symmetries, respectively (Fig. 1). (Note that the crystal axes are denoted here in cubic notation.) Although pristine BaTiO3 is a band insulator with a gap of about 3.2 eV, it can be turned into a semiconductor or metal by doping conduction electrons into Ti- band by means of chemical substitutions or introduction of oxygen vacancies9101112. Specifically, the dilutely doped systems with electron concentration (n) less than 1 × 1020 cm−3 are semiconducting, and exhibit successive ferroelectric-like phase transitions, which manifest as discontinuous changes in resistivity12. On the other hand, the heavily doped systems are metallic down to low temperatures and the resistivity curve shows more moderate temperature dependence without discontinuous jumps. Figure 2(a) exhibits the typical profile of resistivity for a heavily doped single crystal with n = 1.9 × 1020 cm−3. Here, we partially substituted Ba-ions with La ions for electron doping (See Methods). The resistivity shows a metallic behavior, except a cusp-like anomaly around 260 K and a small upturn due to weak localization below 70 K.


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)

Structural phase diagram and schematic view of the macroscopic polarization in electron doped BaTiO3.C, T, O, R and M represent cubic, tetragonal, orthorhombic, rhombohedral and monoclinic, respectively. Arrows denote the direction of macroscopic electric polarization (P). P is pointing toward ,  and  in tetragonal, orthorhombic and rhombohedral phase, respectively, while that in the ‘monoclinic’ phase does to a certain direction in-between  and  direction within  plane. The shaded plane indicates  plane.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f1: Structural phase diagram and schematic view of the macroscopic polarization in electron doped BaTiO3.C, T, O, R and M represent cubic, tetragonal, orthorhombic, rhombohedral and monoclinic, respectively. Arrows denote the direction of macroscopic electric polarization (P). P is pointing toward , and in tetragonal, orthorhombic and rhombohedral phase, respectively, while that in the ‘monoclinic’ phase does to a certain direction in-between and direction within plane. The shaded plane indicates plane.
Mentions: The perovskite BaTiO3 is a prototypical ferroelectric, which is currently utilized in a variety of electronic devices including capacitors, thermistors and nonlinear optical crystals. It shows versatile thermally-induced ferroelectric phases with the macroscopic electric polarization parallel to , and axes as characterized by tetragonal, orthorhombic and rhombohetral crystallographic symmetries, respectively (Fig. 1). (Note that the crystal axes are denoted here in cubic notation.) Although pristine BaTiO3 is a band insulator with a gap of about 3.2 eV, it can be turned into a semiconductor or metal by doping conduction electrons into Ti- band by means of chemical substitutions or introduction of oxygen vacancies9101112. Specifically, the dilutely doped systems with electron concentration (n) less than 1 × 1020 cm−3 are semiconducting, and exhibit successive ferroelectric-like phase transitions, which manifest as discontinuous changes in resistivity12. On the other hand, the heavily doped systems are metallic down to low temperatures and the resistivity curve shows more moderate temperature dependence without discontinuous jumps. Figure 2(a) exhibits the typical profile of resistivity for a heavily doped single crystal with n = 1.9 × 1020 cm−3. Here, we partially substituted Ba-ions with La ions for electron doping (See Methods). The resistivity shows a metallic behavior, except a cusp-like anomaly around 260 K and a small upturn due to weak localization below 70 K.

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.