Jun Kano

Broadband inelastic light scattering of a relaxor ferroelectric 0.71Pb(Ni1/3Nb2/3)O3-0.29PbTiO3

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 polar nanoregions. By the analysis of modified superparaelectric model, the activation energies of fast and slow relaxation processes are determined to be 3.66×103 and 4.31×102K, respectively. The fast process with the lower activation energy probably originated from 180° switching, whereas the slow one with the higher energy from non-180° switching.

Dynamical Properties of Polar Nanoregions of Relaxor Ferroelectric Pb(Ni1=3Nb2=3)O3-0.29PbTiO3

Dynamical properties of the polar nanoregions (PNRs) of a relaxor ferroelectric Pb(Ni 1/3 Nb 2/3 )O 3 –0.29PbTiO 3 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 T d related to the appearance of the PNRs, at T * associated with the growth of the PNRs, and at T f related to the macroscopic structural phase transition; all these temperatures are closely related to the dynamical behavior of the PNRs. The thermal hysteresis around T f in the longitudinal acoustic properties can be interpreted by considering the growth process of the PNRs. From the anomalous acoustic properties, the relaxation time of the polarization fluctuation is evaluated. It is found that the relaxational process responsible for the central peak originates from the polarization fluctuation that is coupled with the longitudinal acoustic mode.

Magnetoelectric effect driven by magnetic domain modification in LuFe2O4.

The magnetocapacitance effect was investigated using impedance spectroscopy on single crystals of LuFe(2)O(4). The intrinsic impedance response could be separated from the interfacial response and showed a clear hysteresis loop below T(Ferri)∼240  K under the magnetic field. The neutron diffraction experiment under the magnetic field proves the origin of the dielectric property related to the motion of the nanosized ferromagnetic domain boundary. These results imply that the modification of the microscopic domain structure is responsible for the magnetoelectric effect in LuFe(2)O(4).

Pure lead nanoparticles with stable metallic surfaces, on perovskite lead strontium titanate particles

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 electron microscopy revealed that the pure lead nanoparticles show structural fluctuations under intense electron-beam irradiation, like gold and platinum nanoparticles.

Exchange Bias in Multiferroic RFe2O4 (R=Y, Er, Tm, Yb, Lu, and In)

An exchange bias (EB) behavior has been observed for multiferroic R Fe 2 O 4 ( R =Y, Er, Tm, Yb, Lu, and In). The materials with small R 3+ ions ( R =Tm, Yb, Lu, and In) exhibit large EB fields (\({\gtrsim}1\) kOe) below ∼100–150 K. This property is rooted in a magnetically glassy state, arising from the competition between ferromagnetic and antiferromagnetic domain interactions. In addition, the EB field tends to be more enhanced for smaller R 3+ ions. Hence, the EB is controlled by the substitution at the R -site in this series.

Nonlinear Electric Conductivity of Charge Ordered System RFe2O4 (R = Lu, Yb)

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 three dimensional charge ordering temperature 340 K. The result is consistent with diffraction observation.

Microstructure and phase transition of MnO2-doped bismuth layered-structure ferroelectrics

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 dielectric permittivity and dielectric loss show that the Mn2+ and Mn3+ ions are preferentially incorporated into the A- and B-sites, respectively, up to a limiting extent of approximately x = 2. The ac conductivity decreases and the activation energy increases with increasing Mn content owing to the decrease in the number of conducting carriers and increase in covalence, respectively. The Curie temperature TC is independent of MnO2 doping within the experimental accuracy, and the dielectric constant satisfies the Curie–Weiss law above TC. The temperature dependence of the soft mode with x = 0 and 1 shows a significant softening towards T1~TC + 113 °C (at T1, the square of the soft mode frequency ωs2→0). ωs2 is approximately proportional to T - T1. These findings indicate that the displacive nature of the phase transition is not affected by MnO2 doping, at least below x = 3.

Characterization of Dielectric Property of Nanosized (Pb0.7Sr0.3)TiO3 Powders Studied by Raman Scattering

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 decrease in particle size. The size dependences of the clamped dielectric constants along the a and c axes characterized by the effect of the phonon confinement are evaluated by the Lyddane–Sachs–Teller relation using the observed frequencies of polar modes with E(x,y) and A1(z) symmetries, respectively.

Broadband Inelastic Light Scattering Study on Relaxor Ferroelectrics

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 enhancement of the correlation length in the PNRs T* and related to a temperature-induced macroscopic structural phase transition Tf. These results are closely related to the behavior of the PNRs. We suggest that two relaxation processes are attributed to the central peak and that the origins of the observed relaxation processes are two types of switching processes of dipole moments in the PNRs. In addition, the activation energy at 0 K has been evaluated as H0B=2.11×103 K.

Piezoelectric (Na0.5K0.5)NbO3-SrTiO3 Ceramics in the Tetragonal-Orthorhombic Phase Boundary Studied by Raman Spectroscopy

Raman spectroscopy of lead-free piezoelectric (1-x)(Na 0.5 K 0.5 )NbO 3 −xSrTiO 3 ceramics and (Na 1 − y Ky)NbO 3 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)(Na 0.5 K 0.5 )NbO 3 −xSrTiO 3 and (Na1 − yKy)NbO 3 at room temperature, the overdamped mode which became soften was found in the intermediate phase at x = 0.05. Although it is difficult to assign the mode because of using ceramics samples, this result has a possibility that the overdamped mode includes the soft mode observed in the orthorhombic phase.