Shinichiro Kawada

(K,Na)NbO3-Based Multilayer Piezoelectric Ceramics with Nickel Inner Electrodes

A lead-free (K,Na)NbO3-based multilayer piezoelectric ceramic with nickel inner electrodes was obtained. Its normalized electric-field-induced thickness strain (Smax/Emax) was 360 pm/V, where Smax denotes the maximum strain and Emax denotes the maximum electric field. This value of 360 pm/V is about half that for the Pb(Zr,Ti)O3-based ceramics that are widely used. However, the (K,Na)NbO3-based multilayer ceramic can achieve comparable displacement to that attainable with Pb(Zr,Ti)O3-based multilayer ceramics by stacking more ceramic layers with smaller thicknesses. Additionally, it is easier to reduce the ceramic-layer thickness by using nickel electrodes. The developed (K,Na)NbO3-based multilayer ceramic is thus considered a good candidate for lead-free piezoelectric actuators.

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.

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 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.

Piezoelectric Properties of Sn-Doped (K,Na)NbO3 Ceramics

It was previously reported that Ca-doped (K,Na)NbO3 + ZrO2 could be cofired with nickel inner electrodes in a reducing atmosphere. In the present study, the piezoelectric properties of Sn-doped (K,Na)NbO3 + ZrO2 ceramics were investigated. We prepared Sn-doped (K,Na)NbO3 + ZrO2 ceramics and Ca-doped (K,Na)NbO3 + ZrO2 ceramics by doping with Sn2+ and Ca2+ under reducing calcination. The Curie temperature Tc of the Sn-doped (K,Na)NbO3 + ZrO2 was 300 °C, which was the same as that of the Ca-doped (K,Na)NbO3 + ZrO2. The tetragonal–orthorhombic phase transition temperature and piezoelectric constant d33 of the Ca-doped (K,Na)NbO3 + ZrO2 were 130 °C and 130 pC/N while those of the Sn-doped (K,Na)NbO3 + ZrO2 were 50 °C and 190 pC/N, respectively. These results suggest that the piezoelectric d constant of (K,Na)NbO3-based multilayer ceramics with nickel inner electrodes can be increased by doping with Sn2+ instead of Ca2+.

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.

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.

Potassium Sodium Niobate-Based Lead-Free Piezoelectric Multilayer Ceramics Co-Fired with Nickel Electrodes

Although lead-free piezoelectric ceramics have been extensively studied, many problems must still be overcome before they are suitable for practical use. One of the main problems is fabricating a multilayer structure, and one solution attracting growing interest is the use of lead-free multilayer piezoelectric ceramics. The paper reviews work that has been done by the authors on lead-free alkali niobate-based multilayer piezoelectric ceramics co-fired with nickel inner electrodes. Nickel inner electrodes have many advantages, such as high electromigration resistance, high interfacial strength with ceramics, and greater cost effectiveness than silver palladium inner electrodes. However, widely used lead zirconate titanate-based ceramics cannot be co-fired with nickel inner electrodes, and silver palladium inner electrodes are usually used for lead zirconate titanate-based piezoelectric ceramics. A possible alternative is lead-free ceramics co-fired with nickel inner electrodes. We have thus been developing lead-free alkali niobate-based multilayer ceramics co-fired with nickel inner electrodes. The normalized electric-field-induced thickness strain (Smax/Emax) of a representative alkali niobate-based multilayer ceramic structure with nickel inner electrodes was 360 pm/V, where Smax denotes the maximum strain and Emax denotes the maximum electric field. This value is about half that for the lead zirconate titanate-based ceramics that are widely used. However, a comparable value can be obtained by stacking more ceramic layers with smaller thicknesses. In the paper, the compositional design and process used to co-fire lead-free ceramics with nickel inner electrodes are introduced, and their piezoelectric properties and reliabilities are shown. Recent advances are introduced, and future development is discussed.