Atsushi Makiya

Crystal-Oriented Bi4Ti3O12 Ceramics Fabricated by High-Magnetic-Field Method

The effect of powder properties on the degree of crystal orientation of Bi4Ti3O12 (BIT) ceramics fabricated by a high-magnetic-field method was investigated. As expected, the degree of orientation of BIT ceramics exhibited little dependence on the crystallinity of the powder, and depended on the particle size of the powder. The degree of orientation increased up to 0.96 when the particle size increased from 0.5 to 1.2 µm. The particle size dependence of the degree of orientation was similar to the relationship between the order parameter and particle size, as derived from Langevins theory on magnetic alignment. This suggests that the crystal orientation of ceramics fabricated by the high-magnetic-field method can be controlled by selecting the particle size of the powder used.

Preparation and Thermoelectric Property of Highly Oriented Al-Doped ZnO Ceramics by a High Magnetic Field

Highly oriented Al-doped ZnO ceramics were prepared by a high magnetic field method and their anisotropic thermoelectric properties were examined. The c-axis oriented specimen along the ab-plane showed a higher electrical conductivity compared to the a-axis and non-oriented specimens as a result of high electron mobility. On the other hand, the differences in the Seebeck coefficients and thermal conductivities between oriented and non-oriented specimens were a small. Consequently, the dimensionless figure of merit of the c-axis oriented specimen increased by about 30% compared to the other specimens.

Fabrication of c-axis oriented higher manganese silicide by a high-magnetic-field and its thermoelectric properties

Fabrication of c-axis oriented higher manganese silicide by a high-magnetic-field and its thermoelectric properties

Crystal-Oriented La-Substituted Sr2NaNb5O15 Ceramics Fabricated Using High-Magnetic-Field Method

To prevent cracking in and improve the piezoelectric properties of what, we fabricated crystal-oriented Sr2-xNa1-xLaxNb5O15 (SNLN) ceramics using the high-magnetic-field method. With increasing amount of La substituted in SNLNs, the bonding strength along the c-axis increased and the crystal anisotropy of coefficient of linear expansion decreased, and as a result cracks were prevented. a–b-plane-oriented SNLNs with Lotgering factors of 0.5 to 0.6 were fabricated. These oriented SNLNs with restrained cracks had lower La contents x≥0.05 than randomly oriented SNLNs. The piezoelectric constant of the oriented SNLNs with x=0.05 had d33=95 pC/N, which increased up to 1.5-fold that of randomly oriented SNLNs. It was apparent that the crystal-oriented SNLN ceramics could show restrained cracks and enhanced piezoelectric properties.

Fabrication of a- and c-axis oriented Zn0.98Al0.02O by a high magnetic field via gelcasting

Highly a- and c-axis oriented Zn0.98Al0.02O ceramics were prepared by a combination of the high magnetic field and gelcasting techniques, and their thermoelectric properties were examined. The gelcasting made it possible to align the particles preferentially along the a- and c-axis within a short exposure time in the high magnetic field. The particle orientation was not degraded and disturbed by the gelation and subsequent processing. The c-axis oriented specimen along the ab-plane showed a higher electrical conductivity compared with the a-axis and non-oriented specimens as a result of high electron mobility. The differences in the Seebeck coefficients between oriented and non-oriented specimens were a very small. This study indicated that applying the magnetic alignment via gelcasting method provides effective and versatile techniques to fabricate the grain oriented materials without hindering the thermoelectric properties

Direct Observation of Alumina Particles Orientation in High Magnetic Field

Introduction Recently, super-conducting magnets were applied for the fabrication of ceramics with unique structures and properties. In a high magnetic field (10T), there is an appreciable interaction between materials and the field even for “non-magnetic” materials such as alumina. Recent study shows that alumina has anisotropic diamagnetic susceptibility as shown in Fig.1, and orients with their c-axis parallel to the magnetic field as shown in Fig. 2. It is interesting to observe directly the process of orientation in the magnetic field. Recently, a new optical method was developed to determine the degree of grains orientation in an alumina compact with a crossed polarized light microscope (ref.1). It has a very high sensitivity even for a very weak orientation, which can not evaluated by the X-ray diffraction analysis. It is very promising to apply this method for directly observing the orientation process of particles in a high magnetic field. However, a microscope made of non-magnetic materials is needed to observe the process of particle orientation in a high magnetic field. In this study, we develop a new crossed polarized light microscope with non-magnetic materials for in-situ observation of particle orientation of alumina grains in a high magnetic field.

Orientation Factor of Grain Oriented Bismuth Titanate Prepared in High Magnetic Field

This paper shows a very promising approach for developing the structure of grain orientation through weak magnetic interaction of ceramics particles in a high magnetic field. Grain oriented bismuth titanate ceramics was successfully developed through a processing in a high magnetic field. XRD and SEM show that c-axes of particles were oriented perpendicular to the applied magnetic field. The orientation structure developed by sintering, and the orientation factor achieved 0.85 as determined using the Lotgering method.