Hirozumi Ogawa

Temperature Dependence of Piezoelectric Properties of Grain-Oriented CaBi4Ti4O15 Ceramics.

Piezoelectric properties of grain-oriented bismuth layer structured compound CaBi4Ti4O15 ceramics and their temperature dependencies were studied. The grain-oriented CaBi4Ti4O15 ceramics were fabricated by the templated grain growth method. The highly preferentially (00l) oriented CaBi4Ti4O15 ceramics were obtained and their Lotgering (00l) orientation degree was almost 100%. The electromechanical coupling coefficient of the longitudinal vibration mode (k33) was approximately three times as large as that of the nonoriented specimen, and the temperature coefficient of resonant frequency (|fr-TC|) was the same as that of the nonoriented specimen. The 24 vibration mode is separated from the 15 vibration mode in the thickness shear vibration of the grain-oriented ceramics. The electromechanical coupling coefficient k15 of the grain-oriented specimen was twice as large as k15 of the nonoriented ceramics, while, k24 was one-third that of k15 of the nonoriented specimen. The |fr-TC| of the 15 vibration mode of the grain-oriented specimen was half that of the 15 vibration mode in the nonoriented ceramics, and that of the 24 vibration mode of the oriented specimen was much larger than that of the 15 vibration mode in the nonoriented ceramics.

Fine-Tolerance Resonator Applications of Bismuth-Layer-Structured Ferroelectric Ceramics

The two-layered SrBi2Nb2O9 (SBN) ceramic resonator that generates second harmonics of the thickness extensional vibration is a strong candidate for fine-tolerance-resonator applications, because of its small electromechanical coupling coefficient and high temperature stability. The Nd substitution of Sr in SBN is effective in further decreasing the temperature coefficient of resonance frequency (TCF) while maintaining its high maximum value of electrical quality factor (Qemax) at a resonance frequency. On the other hand, a grain-oriented SBN-type ceramic resonator has an attractive property of thickness shear vibration. The temperature coefficient of oscillation frequency (TCO) could be less than 10 ppm/°C in an ordinary oscillation circuit with grain-oriented SBN-type ceramics. In this paper, we describe how a fine tolerance resonator can be realized using compositional and structural designs of the bismuth-layer-structured ferroelectric (BLSF) ceramic resonator.

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.

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%.

High-power piezoelectric characteristics of textured bismuth layer structured ferroelectric ceramics

The high-power piezoelectric characteristics in (001) oriented ceramics of bismuth layer structured fer-roelectrics (BLSF), SrBi2Nb2O9 (SBN), (Bi,La)4Ti3O2 (BLT), and CaBi4Ti4Oi5 (CBT), were studied by a constant voltage driving method. These textured ceramics were fabricated by a templated grain growth (TGG) method, and their Lotgering factors were 95%, 97%, and 99%, respectively. The vibration velocities of the longitudinal mode (33-mode) increased proportionally to an applied electric field up to 2.5 m/s in these textured BLSF ceramics, although, the vibration velocity of the 33-mode was saturated at more than 1.0 m/s in the Pb(Mn,Nb)O3-PZT ceramics. The resonant frequencies were constant up to the vibration velocity of 2.5 m/s in the SBN and CBT textured ceramics; however, the resonant frequency decreased with increasing over the vibration velocity of 1.5 m/s in the BLT textured ceramics. The dissipation power density of the BLT was almost the same as that of the Pb(Mn,Nb)O3-PZT ceramics. However, the dissipation power densities of the SBN and CBT were lower than those of the BLT and Pb(Mn,Nb)O3-PZT ceramics. The textured SBN and CBT ceramics are good candidates for high-power piezoelectric applications.

High-Power Characteristics of Thickness Shear Mode for Textured SrBi2Nb2O9 Ceramics

The high-power piezoelectric characteristics of the thickness shear mode for oriented ceramics of bismuth layer structured ferroelectrics (BLSF), SrBi2Nb2O9 (SBN), were studied by the constant current driving method. These textured ceramics were fabricated by the templated grain growth (TGG) method, and the Lotgering factor was 95%. The vibration of the thickness shear mode in the textured SBN ceramics was stable at the vibration velocity of 2.0 m/s. The resonant frequency was almost constant with increasing vibration velocity in the textured SBN ceramics, however, it decreased with increasing vibration velocity in the randomly oriented SBN ceramics. In the case of Pb(Mn,Nb)O3–Pb(Zr,Ti)O3 ceramics, the vibration velocity of the thickness shear mode was saturated at more than 0.3 m/s, and the resonant frequency decreased at lower vibration velocity than in the case of SBN ceramics. The dissipation power density of the textured SBN ceramics was the lowest among those of the randomly oriented SBN and Pb(Mn,Nb)O3–PZT ceramics. The thickness shear mode of textured SBN ceramics is a good candidate for high-power piezoelectric applications.

Piezoelectric Ceramics for High Temperature Applications

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.

High-Power Piezoelectric Characteristics of Textured Bismuth Layer Structured Ferroelectric Ceramics

The high-power piezoelectric characteristics in c-axis oriented ceramics of bismuth layer structured ferroelectrics (BLSF), SrBi2Nb2O9 (SBN), Bi4Ti3O12 (BIT) and CaBi4Ti4O15 (CBT), were studied by constant voltage driving method. These textured ceramics were fabricated by templated grain growth (TGG) method, and their Lotgering factors were 95%, 97%, and 99%, respectively. The vibration velocities increased proportionally to an applied electric field up to 2.5 m/s in these textured BLSF ceramics, although, the vibration velocity was saturated at more than 1.0 m/s in the Pb(Mn,Nb)O3-PZT ceramics. The resonant frequencies were constant up to the vibration velocity of 2.5 m/s in the SBN and CBT textured ceramics, however, the resonant frequency decreased with increasing the vibration velocity of more than 1.5 m/s in the BIT textured 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%.