Kazuo Matsuo

Dielectric and ferroelectric properties of tetragonal tungsten bronze Sr2−xCaxNaNb5O15 (x=0.05–0.35) ceramics

This letter reports the dielectric and ferroelectric properties of tungsten bronze Sr2−xCaxNaNb5O15 (SCNN, x=0.05–0.35) ceramics. Two dielectric anomalies and a diffuse ferroelectric transition behavior were appreciably observed in the compositions of x=0.05–0.25. The incorporation of smaller calcium cations into the crystal structure resulted in an increase in the Curie temperature, from 279 (x=0.05) to 297 (x=0.35), and a decrease in the permittivity, from 1353 to 543, at their respective Curie temperatures. Ferroelectricity was observed in the compositions with x=0.05–0.25, but absent in the compositions with x=0.30 and 0.35 at room temperature. The maximum spontaneous polarization Ps of 9.1 μC/cm2 and remanent polarization Pr of 3.0 μC/cm2 were achieved in the composition of x=0.15.

Optical properties of β-Si3N4 single crystals grown from a Si melt in N2

Large colored β-Si3N4 single crystals were successfully grown from a Si melt in N2. The transmission optical absorption of coloring β-Si3N4 single crystal shows that impurities introduce a midgap level of ∼2.4 eV into the wide band gap of ∼5.3 eV in nondoped Si3N4. The infrared transmission spectrum and electron probe x-ray microanalysis of β-Si3N4 samples show that the solution of the Al element affects the silicon–nitrogen molecular vibration and the states within the band gap of β-Si3N4. The obtained results mean that the Al impurity acts as the radiative center and is the origin of the color in the β-Si3N4 single crystal.

SYNTHESIS OF LARGE-SIZE BETA -SI3N4 CRYSTALS

Large-sized β–Si 3 N 4 crystals up to 10 mm in length and 0.3 mm in diameter with low impurity concentration are successfully grown from silicon melt in a nitrogen atmosphere. By controlling the concentration of impurities in the silicon melt, a new kind of β–Si 3 N 4 crystal, that is, a transparent coloring one with an absorption edge around a wavelength of 520 nm, is obtained.

Particle Impact Damage and Point Load-Induced Fracture Behavior in Zirconia Plasma Spray Coating Film

This study concerns the method for examining the load conditions and evolving stress related to debonding at the coat-substrate interface to identify the responsible factors, by indenting a ceramic coated specimen with a spherical indenter either through impact or quasi-statically under static loading. The morphology of cracks induced by the impact of a foreign object on to specimens of inconel substrate with thermo-resistive coating of zirconia sprayed by two different methods was studied in comparison with the indentation test results by a spherical indenter under static loading. Consequently, the load conditions for coat fracture and debonding at the coat-substrate interface were successfully identified in a plasma spray specimen.

Piezoelectric properties of Sr2-XCaXNaNb5O15 (SCNN) ceramics (0.05<X<0.35) for a smart patch

The study investigating the electrical properties of dense lead-free piezoelectric ceramics in the (1-x)Sr2NaNb5O15-xCa2NaNb5O15 (SCNN) system with x ranging from 0.05 to 0.35 is reported here. Materials were produced with Spark Plasma Sintering (SPS) method. X-Ray diffraction patterns all showed a single tetragonal tungsten bronze phase, peak broadening being seen on increasing the Ca content. The lattice constant calculation indicated distortion and shrinkage of the crystal structure with Ca substitution. Ferroelectric and piezoelectric properties of SCNN greatly depended on the Ca content. The composition with x =0.15 exhibited the greatest polarization with Pr =3.0 μC cm-2and piezoelectric constant of d33 =96 pC/ N, whereas the compositions with x =0.30 and 0.35 almost lost their ferroelectricity and piezoelectricity. Not only investigation of materials properties but also application possibility as a sensor is surveyed. The ultrasonic waves generated by SCNN material as a sensor are much clearer that that by commercially available PZT materials. This study apparently indicates that lead-free SCNN piezoelectric ceramics have potential for electromechanical application.

Effect of the Pretreatment Step Condition in the Growth Process of the Si Melt Method on the Size of β–Si3N4 Single Crystals

Two kinds of obviously different-sized –Si 3 N 4 whiskers were grown from silicon melt with different pretreatment vacuum conditions. Their growth interface structures were studied in a cross-section view from micro-areas to macro-areas by combination of micro-area state analysis with chemical shift mapping of Si K β bands using electron probe microanalysis. The one pretreated under the lower vacuum condition with a rotary pump was 10–20 μm in diameter and hundreds of micrometers in length, and another pretreated under the higher vacuum condition with a diffusion pump was 0.1–0.2 mm in diameter and 2–5 mm in length. The small Si 3 N 4 whiskers were grown from the surface of the SiC particles within the Si melt. The large Si 3 N 4 whiskers were grown from the surface of Si 3 N 4 crucible. On the basis of these results, their growth mechanisms are discussed from the view of the nucleation sites, impurity source, and thermodynamic stability of the SiC particles. Compared with the Si 3 N 4 grains, the SiC particles influenced the nucleation deeply and caused the process to grow small-sized crystals. Preventing the carbon impurities into the Si melt from forming the SiC particles in the pretreatment process was one effective way to grow the large-sized β–Si 3 N 4 single crystals.