Tadashi Sekiya

Piezoelectric Properties of Spark-Plasma-Sintered (Na0.5K0.5)NbO3–PbTiO3 Ceramics

In the search for high-performance piezoelectrics, (1-y)(Na0.5K0.5)NbO3–yPbTiO3 (y≤0.50) solid solution has been prepared using the spark-plasma-sintering method. Dielectric investigation reveals that both the ferroelectric phase transition temperatures and the peak value of the dielectric constant are strongly suppressed in the low y range. However, improved electromechanical coupling constants are observed at the same y range. These properties are explained by considering factors such as composition, crystal structure, ferroelectric domain microstructure, and poling conditions.

High-pressure synthesis and ferroelectric properties in perovskite-type BiScO3–PbTiO3 solid solution

Stabilization of a perovskite-type solid solution (1−x) PbTiO3–x BiScO3 with x⩾0.45 was demonstrated by high-pressure synthesis, and the phase diagram and the ferroelectric properties of the solid solution were investigated. The crystal symmetry of the perovskite subcell change in turn from tetragonal, to rhombohedral, to pseudocubic, to monoclinic, and then to triclinic as x increases. It was found that the tetragonal, rhombohedral, and pseudocubic phases are ferroelectric, while the monoclinic phase is not. In the morphotropic phase boundary in the vicinity of x=0.37 between tetragonal and rhombohedral phases, the maximum electromechanical coupling factor and the minimum coercive electric field were just like those observed in other Pb-based ferroelectric perovskites. In addition, relaxor behavior in the dielectric constant was observed in the vicinity of x=0.5.

MPB Phase Diagram and Ferroelectric Properties in the PbTiO 3 -BiScO 3 System

Perovskite solid solutions (1 m x )PbTiO 3 (PT)- x BiScO 3 (BS) were prepared under ordinary pressure. Single phase tetragonal perovskite was obtained up to the composition x = 0.375, and morphotropic phase boundary (MPB) from tetragonal to rhombohedral phase was also situated on this composition. The dielectric measurements suggested existence of critical compositions around both x = 0.15 and x = 0.3. The Curie temperature ( T c ) was higher than that of PT at x = 0.1-0.2. Below and above x = 0.3, the dielectric constant at T c increased and decreased with increasing BS content, respectively. These dielectric behaviors seemed to be associated with the connectivity of TiO 6 octahedron and ScO 6 octahedron in the perovskite structure.

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.

Phase Diagram of the (Na0.5K0.5)NbO3-ATiO3 Solid Solution

To elucidate mechanisms responsible for the enhanced piezoelectric properties in the potassium-sodium niobate-based solid solutions, phase diagram of the (1 − x) (Na0.5K0.5)NbO3-xATiO3 (A = Sr, Ba, and Pb) systems has been established according to the dielectric constant measurement and the crystal structure analysis results. A tetragonal/orthorhombic morphotropic phase boundary (MPB) is found around x∼ 0.05, where the piezoelectric properties were enhanced. Rietveld refinements show that the tetragonal/orthorhombic MPB is the same as that found in the lead zinc niobate-lead titanate system.

Design of the metal-core piezoelectric fiber

We produced a new piezoelectric fiber with metal core by the hydrothermal method. The insertion of metal core was significant in view that the fragility of ceramics can be overcome and electrodes are not required in the use as sensors and actuators. And new smart board was designed by mounting these piezoelectric fibers on the surface of the CFRP composite. It was shown that these complex fibers function as sensor and actuator in the CFRP board. In order to evaluate the sensor and actuator. However, by the hydrothermal method, piezoelectric layer can be uniformly formed with about 20μm thickness on the titanium wire surface, the PZT clad is insufficient in thickness for the actuator use. In this paper, we solve this problem using extrusion method. We developed the metal core further thicker PZT clad fiber by the extrusion method. 31 piezoelectric fibers were embedded under CFRP composite materials, and the sensor and the actuator function were evaluated. We showed that self sensing was possible using this smart board.

Dielectric Properties of Spark-Plasma-Sintered (Na 0.5 K 0.5 )NbO 3 -PbTiO 3 Ceramics

Dielectric properties of spark-plasma-sintered solid solution (1 m x )(Na 0.5 K 0.5 )NbO 3 m x PbTiO 3 were studied. Both the cubic-tetragonal and the tetragonal-orthorhombic phase transitions become more and more diffuse with increasing x . The strong deviation of the cubic-tetragonal phase transition temperature versus composition curve from the Vegards law is observed. It is considered that (1) the introduction of heterovalence ions to both the perovskite A and B sites, and (2) the change of the mass difference between the perovskite B- and A-site, m B - m A, are two main factors responsible for the observations.

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.

Diffuse Phase Transition of 0.8Pb(Ni1/3Nb2/3)O3-0.2PbTiO3 Single Crystals Studied by Micro-Brillouin Scattering

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 detected. The origins of the anomalies of them are discussed from the phenomenological point of view. The central peak caused by the fluctuation of polarization has been also observed in the VV and VH scattering geometries with the large free spectral range of 150 GHz. It is found the difference of central peak intensity obtained in VV and VH scattering geometries.