ABSTRACT Crystallization process of ferroelectric-based BaTi2O5-glass (BTO125-glass) is studied b... more ABSTRACT Crystallization process of ferroelectric-based BaTi2O5-glass (BTO125-glass) is studied by Raman scattering. Spectral change observed in the present study clarifies successive occurrence of two metastable phases in the crystallization. Variations of spectral intensities on isothermal crystallization are analyzed using Johnson-Mehl-Avrami equation to reveal the crystallization process of each phase. From the result, a homogeneous 3-dimensional growth of α phase and surface 3-demensional growth of β phase are concluded to be taken place gradually in the crystallization.
Multiferroic materials, which offer the possibility of manipulating the magnetic state by an elec... more Multiferroic materials, which offer the possibility of manipulating the magnetic state by an electric field or vice versa, are of great current interest. However, single-phase materials with such cross-coupling properties at room temperature exist rarely in nature; new design of nano-engineered thin films with a strong magneto-electric coupling is a fundamental challenge. Here we demonstrate a robust room-temperature magneto-electric coupling in a bismuth-layer-structured ferroelectric Bi₅Ti₃FeO₁₅ with high ferroelectric Curie temperature of ~1000 K. Bi₅Ti₃FeO₁₅ thin films grown by pulsed laser deposition are single-phase layered perovskit with nearly (00l)-orientation. Room-temperature multiferroic behavior is demonstrated by a large modulation in magneto-polarization and magneto-dielectric responses. Local structural characterizations by transmission electron microscopy and Mössbauer spectroscopy reveal the existence of Fe-rich nanodomains, which cause a short-range magnetic order...
The superconducting transition temperature Tc and the Hall coefficient have been measured on IBi2... more The superconducting transition temperature Tc and the Hall coefficient have been measured on IBi2.2Sr1.8CaCu2O8+y single crystals under hydrostatic pressure. The Tc linearly decreases at the rate dTc/dP~-3.5 K/GPa, indicating the facts that the charge transfer occurs between intercalated iodine atoms and CuO2 layers, and the hole concentration situates in the overdoped region. The facts have been further identified by our Hall-coefficient measurements at ambient pressure, showing an increase of the hole concentration after intercalation. The number of holes transferred from intercalated iodine atoms was calculated to be 0.3 per iodine atom. The pressure derivative of the Hall coefficient is -0.39×10-3 cm3 C-1 GPa-1, which is approximately twice as large as the value on the pristine crystal, indicating the valence change of the intercalated iodine under pressure.
Optical transmittance of Ba 1-x Ca x Ti 2 O 5 (x=0, 0.01, 0.03) bulk glasses of ferroelectric BaT... more Optical transmittance of Ba 1-x Ca x Ti 2 O 5 (x=0, 0.01, 0.03) bulk glasses of ferroelectric BaTi 2 O 5 is measured at room temperature in the wavelength range 190–800 nm. The fundamental absorption edge located in the ultraviolet (UV) region tends to shift toward the longer wavelength region on increasing x. The optical band gap of 3.31 eV estimated for x=0 decreases on increasing x. The decrease in the optical band gap energy is related to the creation of non-bridging oxygen ions, which increase on Ca substitution. The observed increase in the Urbach energy with increasing x is associated with the possible increase of structural disorder in the ferroelectric BaTi 2 O 5-based bulk glass occurred by substituting Ca for Ba .
... We can know the value of Avrami index n from a slope of plot of ln(−ln(1 − [volume fraction])... more ... We can know the value of Avrami index n from a slope of plot of ln(−ln(1 − [volume fraction])) with ln t. As shown in Fig. ... 17360321. References. [1] Y. Takahashi, K. Kitamura, Y. Benino, T. Fujiwara and T. Komatsu, Appl. Phys. Lett. 86 (2005), p. 091110. ...
ABSTRACT Using containerless processing with an aerodynamic levitation furnace, LaO3/2–TiO2 binar... more ABSTRACT Using containerless processing with an aerodynamic levitation furnace, LaO3/2–TiO2 binary glasses were synthesized in bulk form. Glass-forming region was found in the vicinity of eutectic point, which is approximately 29.5% LaO3/2 and 70.5% TiO2 in molar ratio. The glass transition temperature Tg and the crystallization onset temperature Tx of the obtained glasses were determined by differential scanning calorimetry. The thermal stability was evaluated by ΔT (=Tx − Tg). Our experimental results were compared with phase diagram of the LaO3/2–TiO2 binary system. Glass compositions with highest ΔT corresponded to single-phase compound of La4Ti9O24 and the eutectic point.
The knowledge of thermophysical properties of active metals is critical to understand their metal... more The knowledge of thermophysical properties of active metals is critical to understand their metallurgical processes and further industrial applications. However, due to high reactivity and melt contamination from a crucible and gaseous environment, accurate values of the properties are hard to obtain using conventional methods such as the sessile-drop method. In the present study, a vacuum electrostatic levitator was used to circumvent these difficulties and enabled the noncontact determination of thermophysical properties of liquid cerium even in an undercooled state. The data of density, surface tension, and viscosity of molten cerium were reported, as well as their temperature dependence.
Containerless solidification and thermophysical properties of BaTiO3 were studied using a pressur... more Containerless solidification and thermophysical properties of BaTiO3 were studied using a pressurized electrostatic levitation furnace and varying the heating temperature and the cooling rates of several samples. The solid and liquid densities of BaTiO3 over a range of 1220 to 2200K were determined using containerless techniques. A single crystal of hexagonal BaTiO3 grown with this method exhibited a giant permittivity
BaTiO3 samples were aerodynamically levitated and laser melted under containerless conditions and... more BaTiO3 samples were aerodynamically levitated and laser melted under containerless conditions and quenched with a twin-roller apparatus. The microstructure of the BaTiO3 samples became more refined with increasing undercooling level prior to quenching. A two-phase microstructure consisting of perovskite BaTiO3 and hexagonal BaTiO3 was observed in the samples. The dielectric constant of the samples decreased due to the presence of
Binary Al2O3:CaO glasses containing 36-50 mole% Al2O3 were synthesized by containerless processin... more Binary Al2O3:CaO glasses containing 36-50 mole% Al2O3 were synthesized by containerless processing of liquids in nitrogen using aerodynamic and a pressurized electrostatic-aerodynamic levitator. The critical cooling rate for glass formation RC under containerless conditions was ca. 70 K/s. The Vickers hardness of the glasses was 775-785; and the infrared transmission extended to approximately 5500 nm. The work function of the
ABSTRACT Crystallization process of ferroelectric-based BaTi2O5-glass (BTO125-glass) is studied b... more ABSTRACT Crystallization process of ferroelectric-based BaTi2O5-glass (BTO125-glass) is studied by Raman scattering. Spectral change observed in the present study clarifies successive occurrence of two metastable phases in the crystallization. Variations of spectral intensities on isothermal crystallization are analyzed using Johnson-Mehl-Avrami equation to reveal the crystallization process of each phase. From the result, a homogeneous 3-dimensional growth of α phase and surface 3-demensional growth of β phase are concluded to be taken place gradually in the crystallization.
The oxygen-deficient hexagonal BaTiO3 shows huge dielectric constant. Because of the oxygen-defic... more The oxygen-deficient hexagonal BaTiO3 shows huge dielectric constant. Because of the oxygen-deficient induced to change the valance from Ti to Ti and formed the charge imbalance in a lattice. However, this dielectric constant is easily disappeared when the oxygen-deficient is compensated. And it is difficult to control the amount of oxygen-deficient in hexagonal BaTiO3. In this study, the oxygen deficient is substituted by La to keep the charge imbalance. It was successful to retain the huge dielectric constant of La doped hexagonal BaTiO3. La could induce to change the valance from Ti to Ti. And it shows almost the same behavior on the complex plane of Z by an impedance measurement. La doped hexagonal BaTiO3 has a semiconductive behavior.
ABSTRACT Crystallization process of ferroelectric-based BaTi2O5-glass (BTO125-glass) is studied b... more ABSTRACT Crystallization process of ferroelectric-based BaTi2O5-glass (BTO125-glass) is studied by Raman scattering. Spectral change observed in the present study clarifies successive occurrence of two metastable phases in the crystallization. Variations of spectral intensities on isothermal crystallization are analyzed using Johnson-Mehl-Avrami equation to reveal the crystallization process of each phase. From the result, a homogeneous 3-dimensional growth of α phase and surface 3-demensional growth of β phase are concluded to be taken place gradually in the crystallization.
Multiferroic materials, which offer the possibility of manipulating the magnetic state by an elec... more Multiferroic materials, which offer the possibility of manipulating the magnetic state by an electric field or vice versa, are of great current interest. However, single-phase materials with such cross-coupling properties at room temperature exist rarely in nature; new design of nano-engineered thin films with a strong magneto-electric coupling is a fundamental challenge. Here we demonstrate a robust room-temperature magneto-electric coupling in a bismuth-layer-structured ferroelectric Bi₅Ti₃FeO₁₅ with high ferroelectric Curie temperature of ~1000 K. Bi₅Ti₃FeO₁₅ thin films grown by pulsed laser deposition are single-phase layered perovskit with nearly (00l)-orientation. Room-temperature multiferroic behavior is demonstrated by a large modulation in magneto-polarization and magneto-dielectric responses. Local structural characterizations by transmission electron microscopy and Mössbauer spectroscopy reveal the existence of Fe-rich nanodomains, which cause a short-range magnetic order...
The superconducting transition temperature Tc and the Hall coefficient have been measured on IBi2... more The superconducting transition temperature Tc and the Hall coefficient have been measured on IBi2.2Sr1.8CaCu2O8+y single crystals under hydrostatic pressure. The Tc linearly decreases at the rate dTc/dP~-3.5 K/GPa, indicating the facts that the charge transfer occurs between intercalated iodine atoms and CuO2 layers, and the hole concentration situates in the overdoped region. The facts have been further identified by our Hall-coefficient measurements at ambient pressure, showing an increase of the hole concentration after intercalation. The number of holes transferred from intercalated iodine atoms was calculated to be 0.3 per iodine atom. The pressure derivative of the Hall coefficient is -0.39×10-3 cm3 C-1 GPa-1, which is approximately twice as large as the value on the pristine crystal, indicating the valence change of the intercalated iodine under pressure.
Optical transmittance of Ba 1-x Ca x Ti 2 O 5 (x=0, 0.01, 0.03) bulk glasses of ferroelectric BaT... more Optical transmittance of Ba 1-x Ca x Ti 2 O 5 (x=0, 0.01, 0.03) bulk glasses of ferroelectric BaTi 2 O 5 is measured at room temperature in the wavelength range 190–800 nm. The fundamental absorption edge located in the ultraviolet (UV) region tends to shift toward the longer wavelength region on increasing x. The optical band gap of 3.31 eV estimated for x=0 decreases on increasing x. The decrease in the optical band gap energy is related to the creation of non-bridging oxygen ions, which increase on Ca substitution. The observed increase in the Urbach energy with increasing x is associated with the possible increase of structural disorder in the ferroelectric BaTi 2 O 5-based bulk glass occurred by substituting Ca for Ba .
... We can know the value of Avrami index n from a slope of plot of ln(−ln(1 − [volume fraction])... more ... We can know the value of Avrami index n from a slope of plot of ln(−ln(1 − [volume fraction])) with ln t. As shown in Fig. ... 17360321. References. [1] Y. Takahashi, K. Kitamura, Y. Benino, T. Fujiwara and T. Komatsu, Appl. Phys. Lett. 86 (2005), p. 091110. ...
ABSTRACT Using containerless processing with an aerodynamic levitation furnace, LaO3/2–TiO2 binar... more ABSTRACT Using containerless processing with an aerodynamic levitation furnace, LaO3/2–TiO2 binary glasses were synthesized in bulk form. Glass-forming region was found in the vicinity of eutectic point, which is approximately 29.5% LaO3/2 and 70.5% TiO2 in molar ratio. The glass transition temperature Tg and the crystallization onset temperature Tx of the obtained glasses were determined by differential scanning calorimetry. The thermal stability was evaluated by ΔT (=Tx − Tg). Our experimental results were compared with phase diagram of the LaO3/2–TiO2 binary system. Glass compositions with highest ΔT corresponded to single-phase compound of La4Ti9O24 and the eutectic point.
The knowledge of thermophysical properties of active metals is critical to understand their metal... more The knowledge of thermophysical properties of active metals is critical to understand their metallurgical processes and further industrial applications. However, due to high reactivity and melt contamination from a crucible and gaseous environment, accurate values of the properties are hard to obtain using conventional methods such as the sessile-drop method. In the present study, a vacuum electrostatic levitator was used to circumvent these difficulties and enabled the noncontact determination of thermophysical properties of liquid cerium even in an undercooled state. The data of density, surface tension, and viscosity of molten cerium were reported, as well as their temperature dependence.
Containerless solidification and thermophysical properties of BaTiO3 were studied using a pressur... more Containerless solidification and thermophysical properties of BaTiO3 were studied using a pressurized electrostatic levitation furnace and varying the heating temperature and the cooling rates of several samples. The solid and liquid densities of BaTiO3 over a range of 1220 to 2200K were determined using containerless techniques. A single crystal of hexagonal BaTiO3 grown with this method exhibited a giant permittivity
BaTiO3 samples were aerodynamically levitated and laser melted under containerless conditions and... more BaTiO3 samples were aerodynamically levitated and laser melted under containerless conditions and quenched with a twin-roller apparatus. The microstructure of the BaTiO3 samples became more refined with increasing undercooling level prior to quenching. A two-phase microstructure consisting of perovskite BaTiO3 and hexagonal BaTiO3 was observed in the samples. The dielectric constant of the samples decreased due to the presence of
Binary Al2O3:CaO glasses containing 36-50 mole% Al2O3 were synthesized by containerless processin... more Binary Al2O3:CaO glasses containing 36-50 mole% Al2O3 were synthesized by containerless processing of liquids in nitrogen using aerodynamic and a pressurized electrostatic-aerodynamic levitator. The critical cooling rate for glass formation RC under containerless conditions was ca. 70 K/s. The Vickers hardness of the glasses was 775-785; and the infrared transmission extended to approximately 5500 nm. The work function of the
ABSTRACT Crystallization process of ferroelectric-based BaTi2O5-glass (BTO125-glass) is studied b... more ABSTRACT Crystallization process of ferroelectric-based BaTi2O5-glass (BTO125-glass) is studied by Raman scattering. Spectral change observed in the present study clarifies successive occurrence of two metastable phases in the crystallization. Variations of spectral intensities on isothermal crystallization are analyzed using Johnson-Mehl-Avrami equation to reveal the crystallization process of each phase. From the result, a homogeneous 3-dimensional growth of α phase and surface 3-demensional growth of β phase are concluded to be taken place gradually in the crystallization.
The oxygen-deficient hexagonal BaTiO3 shows huge dielectric constant. Because of the oxygen-defic... more The oxygen-deficient hexagonal BaTiO3 shows huge dielectric constant. Because of the oxygen-deficient induced to change the valance from Ti to Ti and formed the charge imbalance in a lattice. However, this dielectric constant is easily disappeared when the oxygen-deficient is compensated. And it is difficult to control the amount of oxygen-deficient in hexagonal BaTiO3. In this study, the oxygen deficient is substituted by La to keep the charge imbalance. It was successful to retain the huge dielectric constant of La doped hexagonal BaTiO3. La could induce to change the valance from Ti to Ti. And it shows almost the same behavior on the complex plane of Z by an impedance measurement. La doped hexagonal BaTiO3 has a semiconductive behavior.
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