Papers by Author: Yukio Sakabe

Abstract: Ceramic materials based on lead titanate, lead niobate and bismuth layer-structured ferroelectrics (BLSF) were studied to develop piezoelectric ceramics for high temperature sensor applications. Compositional modification enabled lead titanate and lead niobate type ceramics to exhibit good piezoelectric properties at 500°C . The Curie temperature for one BLSF, CaBi4Ti4O15 was close to 800°C, though the piezoelectric constant was smaller than those of lead titanate and lead niobate ceramics. These ceramics seem to be good candidates for use as high temperature sensor materials. In addition, textured SrBi2Nb2O9 (SBN), another BLSF, ceramics with various orientation factors were fabricated through the templated grain growth (TGG) method. The resonant frequency of 76% textured SBN varied linearly with temperature and exhibited stable temperature characteristics. The temperature coefficient of the resonant frequency was –0.85 ppm/°C from –50 to 250°C, and was smaller than that of a quartz oscillator. Therefore, textured SBN ceramics are suitable for use as a resonator material when stable resonant frequency is needed in a high temperature range.

Abstract: Atomistic mechanisms that restrain diffusion of oxygen vacancies in BaTiO3 doped with rare earth ions as donors were analyzed using molecular dynamics simulation. It was confirmed that formation of cation vacancies and reduction of lattice volume are sources of resistance for the diffusion. The cation vacancies trap the oxygen vacancies at the nearby O2- sites by an attractive force associated with Coulombic interaction. In contrast, the rare earth ions repel the oxygen vacancies, which migrate via O2- sites, and accelerate the diffusion. This is one of the factors that determine the restraint behavior of the diffusion, which depends on the type of rare earth ion in BaTiO3-based materials.

Abstract: The electrooptic material of transparent (Sr,Ba)Nb2O6 (SBN) ceramics was prepared using the conventional solid-phase reaction process with no special techniques such as hot-pressing or hot isostatic pressing. The SBN ceramics were made transparent by substituting a small amount of Zn2+ ion for the B site (Nb5+ ion site). The Curie temperature was increased by substituting a small amount of Na+ ion for the A site (Sr2+ or Ba2+ site). Furthermore, the orientation of the SBN structure by the template grain growth (TGG) method improved the electrooptic properties of the ceramics.

Abstract: Epitaxially grown (Ba,Sr)TiO3 thin films were prepared on platinum-coated silicon substrate by sol-gel method using a (Ba,Sr)TiO3 sol derived from Ba(CH3COO)2, Sr(CH3COO)2 and Ti(O-i-C3H7)4. The morphology of the films was found to depend on the annealing condition. A columnar structure was obtained for (Ba,Sr)TiO3 thin film by annealing at 800 °C and a columnar grain was found to be single crystal by transmission electron microscope (TEM). The columnar grown film exhibits a preferred (111) orientation that follows the (111) orientation of Pt substrate. Measurement of the C-V in MFM was configured in order to demonstrate good dielectric properties. Obtained films showed high voltage tunability.

Abstract: Piezoelectric properties of potassium niobate (KNbO3; KN) crystal grown using the Vertical Bridgman method were obtained by a resonance-antiresonance method for a length extensional mode. The crystal was poled at 200°C under an electric field of 70 V/mm applied parallel to one of the spontaneous polarization axes. An electromechanical coupling factor (k31) of 0.248, mechanical quality factor (Qm) of 5700, piezoelectric constant (d31) of 9.6 pC/N, elastic compliance (s11E) of 4.02 pm2/ N, and constant (e33T/e0) of 42 were obtained. The optical absorption coefficient of poled crystal has been less than 1.0 cm-1 in the wavelength region of 400-1600 nm. Comparing these values with the reported one for TSSG-KN, indicated that our VB-KN was of good quality.