Kosuke Shiratsuyu

High-Power Piezoelectric Vibration Characteristics of Textured SrBi2Nb2O9 Ceramics

The high-power piezoelectric vibration characteristics of textured SrBi2Nb2O9 (SBN) ceramics, that is bismuth-layer-structured ferroelectrics, were studied in the longitudinal mode (33-mode) by constant current driving method and compared with those of ordinary randomly oriented SBN and widely used Pb(Ti,Zr)O3 (PZT) ceramics. In the case of textured SBN ceramics, resonant properties are stable up to a vibration velocity of 2.6 m/s. Vibration velocity at resonant frequency increases proportionally with the applied electric field, and resonant frequency is almost constant in high-vibration-velocity driving. On the other hand, in the case of randomly oriented SBN and PZT ceramics, the increase in vibration velocity is not proportional to the applied high electric field, and resonant frequency decreases with increasing vibration velocity. The resonant sharpness Q of textured SBN ceramics is about 2000, even at a vibration velocity of 2.6 m/s. Therefore, textured SBN ceramics are good candidates for high-power piezoelectric applications.

Preparation and Dielectric Properties of the Multilayer Capacitor with (Ba, Sr)TiO3 Thin Layers by Metalorganic Chemical Vapor Deposition

Barium strontium titanate ((Ba, Sr)TiO 3 ; BST) thin films were prepared on Pt-coated magnesium oxide single-crystal substrates (Pt(111)/MgO(100) and Pt(100)/MgO(100)) at 650°C by metalorganic chemical vapor deposition (MOCVD). The BST films with a perovskite single phase were obtained. Their room-temperature dielectric constant was 400-590 measured at 100 mV and 1 kHz. The leakage current density was below the order of 10 -7 A/cm 2 at 3V, and the breakdown field was above 500 kV/cm. In addition, the multilayer capacitor with five layers of BST was prepared. The room-temperature capacitance with an effective electrode area of 0.16 mm 2 was 20 nF at 100 mV and 1 kHz. The leakage current was on the order of 10 -8 A at 1V, and on order of 10 -5 A at 3 V.

Piezoelectric Characterization of Low-Temperature-Fired Pb(Zr, Ti)O3–Pb(Ni, Nb)O3 Ceramics

The compositional design of Pb(Zr, Ti)O3–Pb(Ni, Nb)O3 ceramics to lower the sintering temperature and improve their piezoelectric properties was investigated. The nonstoichiometric composition containing excess NiO or PbO and NiO can be densified at 800°C. The excess NiO composition can be fabricated in the firing temperature range of 900 to 1050°C without decreasing the electromechanical coupling factor. Using the new techniques, PZT–Pb(Ni, Nb)O3 ceramics prepared by the conventional powder process can be fired at low temperatures below 1000°C.

Relationship between Vibration Direction and High-Power Characteristics of -Textured SrBi2Nb2O9 Ceramics

The effect of the angle between the vibration direction and the oriented direction on high-power characteristics was investigated for -textured SrBi2Nb2O9 (SBN) ceramics in the longitudinal mode (33 mode). Specimens with their long side formed at angles of 90 and 45° to the -oriented direction were fabricated from a 95%-textured SBN ceramic. Their high-power characteristics were compared with those of a randomly oriented specimen. In the case of the specimen with a 90° angle, the resonant frequency was almost constant during high-vibration-velocity driving. On the other hand, the resonant frequency of the specimen with a 45° angle decreased with increasing vibration velocity as did that of the randomly oriented SBN specimen. Therefore, it is considered that the excellent high-power characteristics of highly textured ceramics depend on the vibration direction for the -textured ceramics. The angle between the vibration direction and the -oriented direction is important in the excellent high-power characteristics of textured SBN ceramics.

Piezoelectric Properties of SrBi2Nb2O9 Textured Ceramics

The textured ceramics of the bismuth layer structured ferroelectrics SrBi2Nb2O9 (SBN)-type compound were fabricated by the templated grain growth (TGG) method, and their characteristics and piezoelectric properties were studied. Platelike particles with a large shape anisotropy, which were needed as template particles in the TGG process, were obtained for the composition with 10% Nd substitution on the Sr site of SBN. Highly (00l) textured Sr0.9Nd0.1Bi2Nb2O9 (SNBN) ceramics were successfully obtained using the TGG process with platelike particles, and the orientation degree of the textured ceramics was 96%. The electromechanical coupling factor of the 96% orientation degree textured ceramics in the thickness shear vibration mode was three times as large as that for the randomly oriented ceramics. The temperature coefficient of the resonant frequency (TCF) of the textured ceramics was +20.9 ppm/°C, whose absolute value was two-thirds of that of the randomly oriented ceramics. The resonant frequency of the textured ceramics increased with temperature, while the resonant frequency of the randomly oriented ceramics decreased with increasing temperature. This result indicated the possibility of obtaining an excellent TCF by the optimization of grain orientation. Therefore, textured ceramics with orientation degrees from 54% to 96% were prepared using template particles of different average diameters, and an excellent TCF of -0.4 ppm/°C was obtained for the specimen with an orientation degree of 76%.

PREPARATION AND CHARACTERIZATION OF EPITAXIAL LINBO3 THIN FILMS BY METAL-ORGANIC CHEMICAL VAPOR DEPOSITION

LiNbO3 thin films were prepared on sapphire substrates by the metal-organic chemical vapor deposition (MOCVD) technique, using lithium dipivaloylmethanate [Li(DPM)] and niobium pentaethoxide [Nb(O–C2H5)5] precursors. LiNbO3 films were deposited on (001) and (012) sapphire substrates and their crystalline structures were investigated by X-ray diffraction and pole figure analyses. The LiNbO3 films deposited on (001) sapphire substrates showed strong (001) orientation involving twin structures, and highly (100)-oriented films were obtained on the (012) sapphire substrates. The full width at half maximum (FWHM) of the X-ray rocking curves of (001)-oriented and (100)-oriented LiNbO3 films were, respectively, 0.16° and 0.21°. Field emission scanning electron microscope (FE-SEM) analysis showed that highly (100)-oriented LiNbO3 films had unique morphologies with long and narrow grains. The grains align in plane on the (012) sapphire substrate, and the c-axis of the LiNbO3 film is parallel to the short axis of the grains.

Highly controlled orientation of CaBi4Ti4O15 using a strong magnetic field

The texture of feeble magnetic ceramics can be controlled by a strong magnetic field. When the magnetic susceptibility of the c axis is smaller than that of the other axes, the c axis aligns perpendicular to the magnetic field; however, the direction is randomly oriented on the plane perpendicular to the magnetic field. The authors demonstrate in this letter that a highly controlled texture in bismuth titanate, which has a c-axis susceptibility smaller than the other axes, can be achieved using a two-step magnetic field procedure. This highly controlled orientation is effective for improving the electromechanical coupling coefficient.

Piezoelectric Properties and Applications of High Qm (Li, Na)NbO3 Ceramics after Heat Treatment

High power piezoelectric characteristics of lithium sodium niobate (Li0.12Na0.88)NbO3 (LNN) ceramics were investigated. Mechanical quality factor Qm of LNN ceramics became around 3000 after a heat treatment at 400oC. This value was about 6 times larger than that before the heat treatment. The heat–treated LNN maintained high Qm value of 1700 even when its vibration velocity was 1.5 m/sec and the temperature rise was about 40oC. The maximum vibration velocity for the heat-treated LNN ceramics is 2 times larger or more than that for conventional lead based high power piezoelectric ceramics. The LNN ceramic is a good candidate material for high power piezoelectric applications.

Reliability of Nickel Inner Electrode Lead-Free Multilayer Piezoelectric Ceramics

The environmental reliability of lead-free (K,Na)NbO3-based multilayer ceramics with nickel inner electrodes was studied. The multilayer specimen with good piezoelectric properties was successfully obtained by adding excess zirconium to a (K,Na)NbO3-based composition. Excess zirconium probably accelerated the solid solution of potassium into the crystal lattice and prevented potassium evaporation. The electric resistivity and piezoelectric properties of the ceramics were extremely stable at a high temperature (85 °C), a low temperature (-40 °C), and a high humidity [85 °C/85% relative humidity (RH)]. Their change rates were below 10% in 500 h studies. The stability was also high in the thermal shock (from -40 to 85 °C) test. It is thus concluded that the (K,Na)NbO3-based composition containing excess zirconium is a good candidate material for nickel electrode multilayer ceramics.

Piezoelectric Properties in Textured Ceramics of SrBi2Nb2O9

A study has been done for the piezoelectric properties in texured ceramics of SrBi2Nb2O9 (SBN) fabricated by the templated grain growth (TGG) method. Remanent polarization along to the stacking direction increased with the orientation degrees. That corresponds to the increases in electro-mechanical coupling coefficient with orientation degree. The temperature coefficient of the resonant frequency (TCF) in thickness sheer vibration mode changed from negative to positive with increasing orientation degrees, and an excellent TCF of -0.4 ppm/°C was obtained for the specimen with an orientation degree of 76%.