Jun Kano

Okayama University · Department of Applied Chemistry and Biotechnology

Barium ferrite particles were synthesized from acicular α-Fe2O3 particles grown in the c-axis direction. The synthesis was carried out by the flux method, in which acicular α-Fe2O3 particles reacted with BaCO3 in NaCO3 flux. The acicular-shaped BaFe12O19 particles grown in the c-axis direction were obtained. The acicular shape consisted of aggregat...

Silica coating is performed onto silver tree‐like fractal structures, which are self‐grown in a solution, through a wet process using tetraethyl orthosilicate. Surface‐enhanced Raman scattering (SERS) of para ‐aminothiophenol ( p ‐ATP) is measured on the silver tree‐like fractal structures with/without silica layer at the excitation wavelength of 5...

Millimeter wave absorption exceeding 70 GHz has been performed in a Co-substituted Ca–La magnetoplumbite (M-type) ferrite. A polymerized complex method was used to increase the substitution of La and Co ions in the M-type ferrite. The increase in the magnetic anisotropy field combined with the remaining significant saturation magnetization results...

We report on a direct measurement method for electrocaloric effects, the heating/cooling upon application/removal of an electric field in dielectric materials, based on a lock-in thermography technique. By use of sinusoidal excitation and multi-harmonic detection, the actual temperature change can be measured by a single measurement in the frequenc...

Single-walled carbon nanotube (SWCNT)/TiO2 hybrids were synthesized using 1,10-bis(decyloxy)decane-core PAMAM dendrimer as a molecular glue. Upon photoirradiation of a water dispersion of SWCNT/TiO2 hybrids with visible light (λ > 422 nm), the hydrogen evolution reaction proceeded at a rate of 0.95 mmol/h·g in the presence of a sacrificial agent (1...

In this study, we report on a direct measurement method for the electrocaloric effect, the heating/cooling upon application/removal of an electric field in dielectric materials, based on a lock-in thermography technique. By use of sinusoidal excitation and multi-harmonic detection, the actual temperature change can be measured by a single measureme...

Silver tree-like fractal structures are self-grown, where needle growths and branching are iterated, via rapid reduction of silver ions in a solution. Many self-similar frameworks exist at different scales in the whole structure, and geometry is characterized by a fractal dimension. Here, we perform a control of the fractal geometry by facile growt...

We report a trial of the valence control for mixed valence iron triangular oxide YbFe2O4 in order to develop an effective technique to control the frustration of charges in strongly correlated electron systems. The electro-chemical doping of Li ⁺ into YbFe2O4 was examined on the cell type sample similar to the Li-ion secondary battery cell. Systema...

At a metal–ferroelectric junction, it has been considered that the electric polarization of the ferroelectric material can affect the electronic structure of the neighboring metal. Here, we demonstrate that the valence state of Pd can be shifted to the unstable high value of 4+ by the electric field of electric polarization in ferroelectric BaTiO3....

We report the band structure of Ba-deficient BaTiO3 as a p-type semiconductor, studied by a combination of light reflectance and photoelectron yield spectroscopy. Two acceptor levels were observed at the tail of a valence band. As the quantity of Ba vacancies increased, the density of state of the two acceptor levels also increased. The levels of t...

(0001)-Oriented epitaxial YbFe 2 O 4−δ films without twin domains were formed on YSZ (111) substrates. The charge ordered structure and the large magnetization comparable to bulk single crystals were confirmed on the films.

Bent band structures have been empirically described in ferroelectric materials to explain the functioning of recently developed ferroelectric tunneling junction and photovoltaic devices. This report presents experimental evidence for ferroelectric band bending, which was observed in the depth profiles of atomic orbitals of angle-resolved hard x-ra...

We report here the formation of carbon–carbon bonds via carbon-hydrogen bond activation catalysed by multi-walled carbon nanotubes (mwcnts), the catalytic activity of which is influenced by nanocarbon morphology and structure. Control of nanocarbon defects and edges allows the realisation of a high-performance carbon-based catalyst that can replace...

Well-crystallized epitaxial YbFe2O4 films were prepared on an α-Al2O3(001) substrate using an Fe3O4 buffer layer. Fe3O4 has a relatively small lattice mismatch with both YbFe2O4 and α-Al2O3. Electron diffraction analysis combined with transmission electron microscopy revealed the epitaxial relationship to be α-Al2O3[110](001) ∥ Fe3O4[](111) ∥ YbFe2...

We decorated nano-crystalline LiNbO3 (LN) particles, which played the role of artificial solid electrolyte interfaces (SEIs) on an active material, namely LiCoO2 (LC). Conventional one-step synthesis using metal organic decomposition (MOD) was used initially, but resulted in the presence of an undesired Li-rich compound, Li3NbO4 (L3N), along with a...

We report a possible charge ordering model of triangular mixed valence material YbFe2O4. It was found that a crystal synthesized with high stoichiometry on iron vacancy shows new and simple extinction rule in the superlattice reflections. The Laue class of the diffraction signal is expressed as 2/m. With the consideration of the charge neutrality a...

Levels of the conduction band minimum and the valence band maximum in ion-deficient BaTiO3 particles were investigated with optical band gap and ionization energy measurements. Though it is known that the quantification of the band structure in an insulator is difficult, due to the poor electrical conductivity of BaTiO3, systematic variation in the...

Rare-earth iron oxides (RFe2O4) have attracting attention as new electronic device materials because of their numerous functionalities, such as electronic ferroelectricity, ferrimagnetism, and high infrared absorption. In this paper, nearly monophasic Y bFe2O4 films were prepared on α-Al2O3(001) substrates by the spin coating method using an aqueou...

We report the effect of iron vacancies on the magnetic property of spin and charge ordered system YbFe2O4 single crystals. The excess amount of iron compensates for the evaporation of iron during crystal growth. We concluded that samples grown with the standard method contain iron vacancies of more than 10%. It is considered that increasing the iro...

We give a brief review of the experimental research on a triangular mixed valence iron oxide RFe2O4 (R = Y, Dy, Ho, Er, Tm, Yb, Lu, Sc or In). Interest in this material has been increasing every year because of the fascinating but complicated interaction between spin, charge and the orbital state of iron ions in frustrated geometry. Reports collect...

Precise measurements of specific heat were performed on high quality single crystals of multiferroic LuFe2O4 by using an ac calorimeter. The thermal anomalies corresponding to four known phase transitions were observed at 220 K (T g), 260 K (TN), 380 K (T3CO) and 590 K (T2CO). In addition to them, a new clear anomaly was detected at 305 K. No other...

Various types of iron oxides loaded on ferroelectric BaTiO3 and nonferroelectric ZrO2 supports have been studied by 57Fe Mössbauer spectroscopy to investigate the valence instability of iron oxides affected by ferroelectric polarization fluctuation. Although the iron oxide loaded on ZrO2 shows a typical reduction process at high vacuum and high tem...

Rare-earth iron oxides (RFe2O4) have attracting attention as new electronic device materials because of their abundant functionalities such as ferroelectricity, ferrimagnetism, and high infrared absorption. These properties are strongly related to the mixed iron valance states between Fe²⁺ and Fe³⁺. We tried to prepare RFe2O4 films by using soft ch...

Photoinduced ferrimagnetic to antiferromagnetic transition was investigated in double layered Fe oxide LuFe2O4 by 12fs infrared pulse. Inter-layer charge imbalance successively induce the changes of charge/magnetic structures interacting with several phonons through the exchange interaction.

We report nonlinear conductivity associated with a phase transition in polar charge ordered material YbFe2O4. To investigate the existence of nonlinear conductivity, we measured temperature dependence of conductivity as a function of applied electric current and estimated the sample heating precisely. Then we found the nonlinear conductivity below...

Magneto-capacitance effect was investigated using the impedance spectroscopy on single crystals of LuFe2O4. The intrinsic impedance response could be separated from the interfacial response and showed a clear hysteresis loop below TFerri ~ 240 K under the magnetic field. The neutron diffraction experiment under the magnetic field proves the origin...

We synthesized well-crystallized ilmenite-type FeGeO3 to investigate its structural and magnetic properties. Ilmenite-type FeGeO3 were synthesized by high-pressure synthesis technique using a Kawai-type multi-anvil apparatus. Their structural and magnetic properties were examined by XRD analysis with Rietveld refinement, transmission electron micro...

The change of electrical and lattice dynamical properties of ferroelectric Ca0.6Sr0.4Bi4Ti4O15 (CSBT) ceramics were studied by doping with 0.1 wt.% of CeO2 and MnO2. The loss tangent and the AC conductivity decreased markedly due to the reduction of charge carrier. The activation energy of doped-CSBT increased owing to the reduction of intrinsic de...

57Fe Mössbauer spectroscopy was performed on two types of Fe oxide nanoparticles supported on a typical ferroelectric, BaTiO3. It was found that the valence state of FeO nanoparticles changed to a mixed 2+/3+ state at high temperature where BaTiO3 shows paraelectric behaviour. We attribute this phenomenon to the fluctuation of electric dipoles whic...

An exchange bias (EB) behavior has been observed for multiferroic RFe2O4 (R = Y, Er, Tm, Yb, Lu, and In). The materials with small R3þ ions (R = Tm, Yb, Lu, and In) exhibit large EB fields (>1 kOe) below 100-150 K. This property is rooted in a magnetically glassy state, arising from the competition between ferromagnetic and antiferromagnetic domain...

Magnetic and dielectric properties have been investigated for Bi2CuO4, which has the same chemical formula as that of the parent materials of cuprate superconductors R2CuO4 (R: rare earths). Magnetization measurements show the antiferromagnetic transition of the Cu2+ spins at ∼42K, as reported previously. Dielectric measurements for the frequencies...

The frequency dependence of the complex dielectric constant of LuFe2O4 single crystal is measured by terahertz time-domain spectroscopy. We observed a broad infrared active mode in the real and imaginary parts of the complex dielectric constants at around 25 cm−1.

The low-frequency light scattering spectroscopy always encounters experimentally a difficulty near the phase transition point due to the overlapping between the soft mode spectra and the strong elastic-scattering component originated from the surface and/or imperfections irradiated by the laser light. A time-resolved phonon spectroscopy, the cohere...

Dynamical properties of protonic conductor K3H(SeO4)2 were examined by using various techniques, Brillouin scattering, quasi elastic, and inelastic neutron scattering. No significant anomaly was observed in longitudinal and transverse acoustic modes. In each experiment, a Lorentzian shaped spectrum was observed at extremely low energy, (less than 0...

A characteristic nonlinear electric responses were found in a charge ordered type ferroelectrics LuFe2O4 with less oxygen deficiency. Cole – Cole circular in the dielectric response varies in the function of the amplitude of the AC electric field. With a synchrotron radiation diffraction experiment under the current revealed the variation of the co...

The variation of AC dielectric constant in the function of the DC magnetic fields was found in low oxygen vacant LuFe2O4 single crystal in which the electric polarization arise from the polar charge ordering. These magneto-electric coupling should be explained by a novel mechanism where the boundary motion of the polar charge ordered domain is affe...

Brillouin and Raman spectra of a 0.71Pb(Ni1/3Nb2/3)O3-0.29PbTiO3 single crystal were measured in two light scattering geometries to elucidate the origins of central peaks that is related to the dynamics of the polar nanoregions. Two Lorentzian-type central peaks exist in the Brillouin spectra. The shape and the full width at half maximum of the bro...

Ferroelectric lead-based perovskite particles have been fabricated by co-precipitation method which a Ca or Ba modified Pb site. Co-precipitates were first synthesized at ambient temperature and then annealed in air at various temperatures to produce lead-base perovskite particles. We demonstrate that the morphology, crystal structure and soft mode...

The size effects on the successive phase transition of lanthanum doped ferroelectric bismuth titanate Bi3.5La0.5Ti3O12 (BLT) nano-particles have been investigated. A dielectric anomaly appears around 520°C for all the size of nano-particles, corresponds to the low temperature monoclinic to orthorhombic phase transition that remains unaffected by th...

The dynamical properties of protonic conductor K3H(SeO4)2 were examined by Brillouin scattering. Both longitudinal-acoustic modes (c33 and c11) and a transversal mode (c44) monotonously depend on temperature, and no soft mode was observed. A central mode with a width about 6 GHz was observed above phase-transition temperature, TC. The central mode...

High-resolution synchrotron X-ray powder diffraction measurement with multiple-detector system has been performed to investigate the scaling effect in ferroelectric PbxSr1-xTiO3 nanoparticles at ambient temperature with various sizes ranging from 10 to 200 nm and various compositions. The peak profiles of the 200 reflections show a large broadening...

The effects of MnO2 doping on the microstructure and phase transition of ferroelectric CaBi4Ti4O15 (CBT) ceramics with x mol % of MnO2 (CBT-xM; x = 0, 1, 3) have been studied. The single-phase crystal structure and the plate-like grain morphology are clearly observed for all compositions, while extended grains are observed with x = 3. The dielectri...

We demonstrate an efficient method of fabrication for pure lead nanoparticles with non-oxidized surfaces, supported on perovskite lead strontium titanate particles with a size distribution from tens to several hundreds of nanometers. The fabrication method is based on co-precipitation and subsequent annealing in air at 600 degrees C. Transmission e...

Synchrotron radiation x-ray diffraction measurement was performed to investigate the size effect in ferroelectric nanosized (Pb(0.7)Sr(0.3))TiO(3) particles with various sizes ranging from 10 to 200 nm. The 200 and 002 Bragg reflections were separated using low energy synchrotron radiation x-rays. The peak profiles of the 002 reflections show a lar...

An efficient fabrication method for pure lead nanoparticles supported on lead-based perovskite particles has been developed using co-precipitation. The annealing of the co-precipitates in air at 600°C produced lead nanoparticles with non-oxidized and non-contaminated surfaces. High-resolution transmission electron microscopy revealed that the pure...

Raman scattering of lead nickel niobate Pb(Ni1/3Nb2/3)O3 (PNN) single crystals grown by the flux method has been performed to investigate the temperature dependence of the optical phonons of relaxors. Anomaly of the temperature dependence of the Raman intensity at 780 cm was observed. Polar microregions promote the growth of volume gradually above...

Bi4 − xLaxTi3O12 (BLT) nano-particles have been synthesised by the chemical co-precipitation method utilizing a polymeric precursor. The particle size decreases from 100 to 40 nm with the increase of La content (x = 0 ∼ 1) owing to the increase of a reaction temperature. The axial ratio a/b of BLT decreases with the increase of La content reflects...

Dynamical properties of the polar nanoregions (PNRs) of a relaxor ferroelectric Pb(Ni1/3Nb2/3)O3-0.29PbTiO3 single crystal are studied by using Brillouin scattering to elucidate the mechanism of the diffuse phase transition. The temperature dependence of Brillouin scattering shows anomalies at three temperatures: at Td related to the appearance of...

We have studied structural and vibrational properties of Ca-doped lead titanate ceramics. The vibrational soft modes associated with the ferroelectric phase transition have been observed. A(1)(1TO) mode, which is one of the soft modes, has four subpeaks due to anharmonicity. Composition and temperature dependences of subpeak frequencies of the A(1)...

Abstract-Structural phase transitions in relaxor ferroelectric materials remain to be one of the most puzzling issues in materials science. In the present work, we have investigated relaxational and vibrational properties of a relaxor ferroelectric 0.71Pb(Ni(1/3)Nb(2/3))O(3)-O.29PbTiO(3) single crystal by means of inelastic light scattering measure...

Nanosized perovskite (Pb0.7Sr0.3)TiO3 powders have been studied by Raman scattering to characterize the dielectric property derived from the particle size effect. All the optical phonons were assigned while referring to previously reported Raman spectra of PbTiO3. The frequencies of the soft E(1TO) and A1(1TO) modes show a slight hardening with a d...

Dielectric and light scattering studies on a Pb(Ni1/3Nb2/3)O3-0.29PbTiO3 single crystal have been conducted in a wide temperature range to clarify the relaxational properties of polar nanoregions (PNRs). The temperature dependences of the relaxation time observed in light scattering spectra show two characteristic temperatures: associated with enha...

We have studied the aging effect of bismuth sodium titanate (BNT) ceramics with point defects. With aging BNT ceramics, we have observed slight decrease in BNT permittivity. Permittivity vs. aging time is well reproduced by assumed Debye-relaxation. It is found that there are two relaxation processes in this aging effect. The diffuseness of phase t...

Structural phase transitions in relaxor ferroelectric materials remain to be one of the most puzzling issues in solid-state physics. In the present work, we have investigated relaxational and vibrational properties of a relaxor ferroelectric 0.71Pb(Ni_1/3Nb_2/3)O₃-0.29PbTiO₃ single crystal by means of inela...

The MnO2 doping effect on ferroelectric phase transitions of CaBi4Ti4O15 ceramics has been studied by Raman scattering, dielectric measurements and scanning electron microscope. The Curie temperatures show monotonic decrease as the content of MnO2 increases. Softeing of low frequency optical modes has been observed for all the compositions, while t...

Brillouin scattering in the relaxor ferroelectric 0.8 Pb(Ni 1/3 Nb 2/3 )O 3 -0.2 PbTiO 3 has been studied in the temperature range from −150°C to 500°C. The anomalies of the frequency shift and full width at half maximum of Brillouin component at the structural phase transition from the paraelectric to ferroelectric phases have been successively de...

Raman spectroscopy of lead-free piezoelectric (1-x)(Na0.5K0.5)NbO3−xSrTiO3 ceramics and (Na1 − yKy)NbO3 ones sintered by the Spark-Plasma-Sintering method have been performed to investigate the dynamical property in the intermediate phase of x = 0.05. From the comparison of Raman spectra between (1-x)(Na0.5K0.5)NbO3−xSrTiO3 and (Na1 − yKy)NbO3 at r...

Lead-free piezoelectric (1-x)(Na0.5K0.5)NbO3−xSrTiO3 ((1-x)NKN- xST) solid solution has been fabricated around a morphotropic phase boundary (MPB) by Spark-Plasma-Sintering method. The phase diagram around MPB was studied by the dielectric measurement. The piezoelectric constant d33 and electromechanical constant kp measurements shows that MPB is a...

The elastic properties of propylene glycol (PG) were studied by Brillouin scattering between 100 K and 442 K using a high-resolution Fabry–Perot interferometer. The acoustic phonon velocity, phonon damping, and relaxation time were measured as functions of temperature. At high temperatures, the temperature dependence of the relaxation time obeyed t...

Brillouin and Raman scatterings of a 0.71Pb(Ni1/3Nb2/3)O3-0.29PbTiO3 single crystal have been measured to investigate broadband inelastic spectra. The two different central peaks related to fast and slow relaxation processes have been observed separately. These two processes are attributed to the thermally activated switching of polarization in pol...

この論文は国立情報学研究所の電子図書館事業により電子化されました。 研究会報告 水・エタノールニ成分混合系について室温で低振動ラマン散乱スペクトルを測定し、低濃度を重点的に詳細な濃度依存性を調べた。低濃度において180cm^<-1>のモードの動的感受率の虚部が大きく減少していることが分かった。

Brillouin scattering of water-ethanol binary mixtures have been measured in the temperature range from room temperature to 343 K as a function of ethanol concentration. A maximum appears at 12 ethanol mol% in the sound velocity and at about 50 mol% in the absorption coefficient alpha/f2 at room temperature. Raman scattering of heavy water-ethanol m...

A new heterodyne experiment on the ferroelectric KH2PO4 elucidates the extremely early stage of the excitation process of the ferroelectric relaxation mode. The time dependence of the response function G(t) shows a continuous rising from the time origin where the mode is excited by the ultra-short femtosecond pulses. The limit of the Debye model is...

Femtosecond Impulsive stimulated Raman scattering of KD2PO4with an optical heterodyne detection has been applied to elucidate the ultra short-time dependence of the response function G(t) associated with a ferroelectric B2soft mode above Tc. In a time region 0∼200 fs, where the B2mode was excited at t=0 fs, G(t) shows clearly the existence of an in...

It has been reported that the ferroelectric B 2 soft mode of KDP in time-domain was observed directly by the impulsive stimulated Raman scattering with a heterodyne detection method (HD-ISRS). With 80 femtosecond laser pulses, the initial process in the extremely early stage of the B 2 mode excitation observed for the first time in time-domain. The...

The femtosecond time-resolved spectroscopy has been applied for the study of the B2 soft mode in the phase transition of the hydrogen-bonded ferroelectric KDP. An extremely early stage of the excitation of the B2 soft mode in KDP reveals newly existence of the mechanical forming process of the soft modes over the limit of the Debye model. The metho...

The ferroelectric B-2 soft mode of KDP has been observed directly in time domain by the impulsive stimulated Raman scattering with a heterodyne detection method (HD-ISRS). HD-ISRS system gives the time dependence of the B-2 mode with an excellent signal to noise ratio near the ferroelectric phase transition temperature. With 80 femtosecond laser pu...