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The precursor dynamics of ferroelectric phase transitions in relaxor-based ferroelectric (1 - x) Pb(Zn1/3Nb2/3)O3-xPbTiO3 single crystals, with x = 0.07, 0.10, and 0.12, were investigated using inelastic light scattering from a longitudinal acoustic phonon. An acoustic anomaly in a broad temperature range, which is characteristic of relaxor ferroelectrics, was observed. We describe the anomalies in the paraelectric phase by assuming local piezoelectric coupling inside polar nanoregions, which are surrounded by a nonpolar matrix. On the basis of local piezoelectric coupling, a relaxation time τ and a dynamic characteristic length L of the order-parameter (polarization) fluctuations were determined to be in the order of 10-13s and 10-9 m, respectively. The τ and L values increase sharply upon cooling from high temperatures but more gradually below the intermediate temperature T* (=493 - 510 K). This result implies that the local polarization fluctuations grow rapidly upon cooling down to above T* and the growth rate decreases below T*. The inflexion point of this growth process in the paraelectric phase is related to the characteristic properties of relaxor-based solid solutions. [ABSTRACT FROM AUTHOR]

Acoustic properties of the ferroelectric PbTiO3 single crystals were studied at temperatures near the phase transition temperature (T c) by Brillouin scattering and compared to those of BaTiO3. The Brillouin frequency shift of the longitudinal acoustic mode of PbTiO3 showed a mild softening and a subsequent discontinuous change at T c indicating the change in the crystal structure from cubic (m3m) to tetragonal (4mm) symmetry. The Brillouin linewidth exhibited appreciable values in the paraelectric phase suggesting electrostrictive interactions between the acoustic modes and polarization fluctuations induced by local distortions due to off-centered displacements. However, in contrast to BaTiO3, there was no strong temperature-dependent central peak in the paraelectric phase of PbTiO3. This may indicate that there is no long-living precursor polar cluster in the cubic phase, consistent with the strong displacive nature of the ferroelectric phase transition in this compound. [ABSTRACT FROM PUBLISHER]

The effect of annealing in Ar-atmosphere on TC is investigated in ferroelectric single crystals of 10%KF-substituted BaTiO3 (Ba0.9K0.1TiO2.9F0.1: KF-BT/0.10) through the dielectric properties. The marked increase in TC is observed; TC increases from 323 K to 367 K after it is annealed at 1473 K. Combined with our previous results on the O2 annealing, we consider that the increase in TC originates from the evaporation of F ions which has the largest electronegativity of all elements. TC of the Ar- annealed KF-BT/0.10 is almost same as that of O2- annealed sample (TC ∼ 371 K), indicating that amount of F ions in the sample determines TC regardless of the annealing atmosphere. [ABSTRACT FROM AUTHOR]

Broadband inelastic light scattering spectra of (1-x)(Na0.5Bi0.5)TiO3-xBaTiO3 single crystals are measured in the frequency range between 1 GHz and 20 THz to investigate the peculiar behavior of the polarization and the origin of diffusive dielectric anomaly. In the light scattering spectrum in the 1GHz-10 THz range, a quasielastic central peak (CP) is observed, while in the light scattering spectrum in the 1 THz-20 THz, optical phonon modes are observed. The central peak shows the remarkable narrowing toward the peak temperature of dielectric constant Tm on the cooling from the high temperature for above Tm, this fact indicates that the relaxation of polarization shows slowing down towards Tm. The contribution of the relaxation of polarization to the dielectric property can be demonstrated using the generalized Lydanne-Sachs-Teller (LST) relation including the relaxation modes. The calculated value by the generalized LST relation shows good agreement with observed dielectric constant. This fact suggests that the relaxation of local polarization causes the anomaly of the dielectric constant. The diffusive peaks of the dielectric constant and the relaxation time determined from the CP are reproduced by the extended Curie-Weiss law and the stretched critical slowing down to evaluate the diffuseness of these peaks quantitatively. With increasing of x, these peaks become more diffusive. This result strongly suggests that the diffuseness of these peaks is related to the strength of the random field generated by the disordering of cations at A-site in perovskite structure. [ABSTRACT FROM AUTHOR]

It was found that the photoelectrochemical performance and photocatalytic activity of rod-type TiO electrodes were affected by various post-calcination treatments, for example, calcination in NH or under vacuum. Post-calcination treatment in NH at 773 K was particularly effective in increasing the photoelectrochemical performance and photocatalytic activity of rod-type TiO electrodes. A unique photoelectrochemical circuit was constructed by connecting a rod-type TiO electrode to a Pt electrode through a silicon solar cell in which the negative bias was applied on the rod-type TiO electrode. It was found that the photoelectrochemical circuit can effectively oxidize ethanethiol in water into CO. [ABSTRACT FROM AUTHOR]

The phase transition temperatures and piezoelectric properties of (Bi0.5Na0.5)TiO3 (BNT) ceramics and single crystal were investigated. This study revealed that the high conductivity of BNT ceramics is attributed to the Bi vaporization during sinterint. The highest depolarization temperature Td of 187°C was obtained for the stoichiometric BNT ceramics, and Td tends to decrease as the composition deviates from stoichiometric BNT. Td of BNT single crystal was 158°C because of Na poor composition. BNT ceramics was easy to pole fully when the Bi/Na ratio is more than 1.0. The electromechanical coupling factor k33 and piezoelectric properties d33 of fully poled stoichiometric BNT ceramics were 0.459 and 72.9 pC/N, respectively. [ABSTRACT FROM AUTHOR]

A unique photoelectrochemical circuit system was constructed by connecting a rod-type TiO2 electrode with a Pt electrode through a silicon solar cell. The photoelectrochemical circuit system efficiently oxidized ethanethiol in water into CO2, while the reaction rate strongly depended on the calcination temperature of the rod-type TiO2 electrode. Furthermore, it was found that a negative bias applied to the rod-type TiO2 electrode by a silicon solar cell enhances the oxidation rate of ethanethiol in water. [ABSTRACT FROM AUTHOR]

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 O.71Pb(Ni1/3Nb2/3)O3-O.29PbTiO3 single crystal by means of inelastic light scattering measurements. Analysis based on the spectra has shown anomalous behaviors at Burns' temperature Td, freezing temperature Tf, those are related to a development of polar nanoregions (PNRs). The PNR must play a key role in the relaxor nature, and obtained results provide new insights into the relaxational dynamics in the PNRs and into how they develop below Tf. [ABSTRACT FROM AUTHOR]

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 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. [ABSTRACT FROM AUTHOR]

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 4.31×102 K, 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. [ABSTRACT FROM AUTHOR]

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 4.31×102 K, 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. [ABSTRACT FROM AUTHOR]

The dynamical properties of polar nanoregions have been investigated in Pb[(In1/2Nb1/2)0.65Ti0.35]O3 single crystals by Brillouin scattering. Longitudinal acoustic phonons begin to show softening below the Burns temperature TB∼700 K. The Brillouin shift in the longitudinal acoustic phonon mode exhibits clear anomalies at the cubic–tetragonal phase transition temperature of around Tct∼550 K and at the tetragonal–rhombohedral one of around Ttr∼460 K. Broad and narrow central peaks begin to appear below TB and the intermediate temperature T*∼600 K, respectively. Relaxation rate was calculated in the longitudinal phonon mode and central peaks. Below T*, the relaxation rate calculated from the longitudinal phonon mode agrees well with that of the broad central peak, suggesting the coupling between local polarization and strain fluctuations due to the formation of long-lived polar nanoregions. The polarization of the central peaks in the cubic phase suggests that polar nanoregions have the tendency to form long-range polar ordering. [ABSTRACT FROM AUTHOR]