Yutaka Doshida

Miniature Cantilever-Type Ultrasonic Motor Using Pb-Free Multilayer Piezoelectric Ceramics

A Miniature cantilever-type ultrasonic motor was fabricated using multilayer piezoelectric ceramics (MLPC) made of (Sr,Ca)2NaNb5O15 (SCNN), a Pb-free piezoelectric material, and the electrical driving properties were investigated. The displacement of SCNN-MLPC was 177 nm at 100 V, which was 10-fold the voltage of MLPC made of Pb(Zr,Ti)O3–Pb(Ni,Nb)O3–Pb(Zn,Nb)O3 (PZT). The ultrasonic motor using SCNN-MLPC started to rotate at 3.8 Vp–p, and showed the following characteristics: a revolution speed of Ω0=517 rpm, a torque of T0=1.4 µN m, and an efficiency of η=7% at 13.4 Vp–p. The power consumption, in this case, was 0.3 mW, which is not so high. On the other hand, an ultrasonic motor of the same form made of PZT-MLPC showed Ω0=610 rpm, T0=1.6 µN m, and η=9% at 1.9 Vp–p, and the same power consumption as the SCNN motor. That is, it was found that the SCNN motor was not so different from the PZT motor in terms of their characteristics; however, the SCNN motor needed 10 times as high a voltage as the PZT motor in electrical driving. In conclusion, it can be said that we succeeded in realizing a miniature cantilever-type ultrasonic motor using Pb-free MLPC.

Crystal-Oriented Bi4Ti3O12 Ceramics Fabricated by High-Magnetic-Field Method

The effect of powder properties on the degree of crystal orientation of Bi4Ti3O12 (BIT) ceramics fabricated by a high-magnetic-field method was investigated. As expected, the degree of orientation of BIT ceramics exhibited little dependence on the crystallinity of the powder, and depended on the particle size of the powder. The degree of orientation increased up to 0.96 when the particle size increased from 0.5 to 1.2 µm. The particle size dependence of the degree of orientation was similar to the relationship between the order parameter and particle size, as derived from Langevins theory on magnetic alignment. This suggests that the crystal orientation of ceramics fabricated by the high-magnetic-field method can be controlled by selecting the particle size of the powder used.

Double-Mode Miniature Cantilever-Type Ultrasonic Motor Using Lead-Free Array-Type Multilayer Piezoelectric Ceramics

We studied the following to improve the characteristics of the lead-free ultrasonic micromotor. A double-mode miniature cantilever-type ultrasonic motor was fabricated using array-type multilayer piezoelectric ceramics (A-MLPC) of (Sr,Ca)2NaNb5O15 (SCNN) such as lead-free piezoelectric materials, and the electrical driving properties were investigated. The A-MLPC integrated multilayer piezoelectric ceramics (MLPC) arrayed in a 2 ×2 matrix. By using A-MLPC, double-mode bending vibration of the stator vibrator can be realized easily, and the quality factor of the vibrator increased. Furthermore, with the improvement of the piezoelectric properties of the SCNN, the electromechanical coupling coefficient of the vibrator increased. As a result, we succeeded in improving the driving properties of the motor. In particular, the driving voltage of SCNN motor decreased to 1/10 of the previous study, and this motor is similar to Pb(Zr,Ti)O3–Pb(Ni,Nb)O3–Pb(Zn,Nb)O3 (PZT) one in terms of properties by applying 3 times higher voltage than that required for the PZT one. The SCNN motor started to rotate at 0.3 Vp–p and showed such characteristics as revolution speed of 730 rpm, torque of 0.7 µN m, and efficiency of 3.5% at 1.6 Vp–p. It appeared that the SCNN motor was able to rotate by a lithium-ion cell used in the mobile equipment without an amplifier circuit.

Possibility of Cofiring a Nickel Inner Electrode in a (Na0.5K0.5)NbO3–LiF Piezoelectric Actuator

Multilayer (Na0.5K0.5)NbO3 (NKN) ceramics are considered promising candidates for lead-free piezoelectric actuators. The possibility of cofiring a nickel inner electrode in an NKN–LiF ceramic was investigated by evaluating the electrical properties and microstructures. The fabricated Ni inner electrode multilayer actuator sintered in a reduced atmosphere exhibited comparable dielectric properties to those of bulk NKN ceramics. The electric-field-induced strain was approximately 210 pm/V. Analysis based on the Rayleigh model showed that the extrinsic non-180° domain wall motion was suppressed in the multilayer structure. The microstructure of the NKN ceramic was not affected by cofiring with nickel, and the NKN/Ni interface was both compositionally and structurally sharp. These results imply that the NKN–LiF ceramic can be cofired with nickel without any deterioration of its properties.

Crystal-Oriented La-Substituted Sr2NaNb5O15 Ceramics Fabricated Using High-Magnetic-Field Method

To prevent cracking in and improve the piezoelectric properties of what, we fabricated crystal-oriented Sr2-xNa1-xLaxNb5O15 (SNLN) ceramics using the high-magnetic-field method. With increasing amount of La substituted in SNLNs, the bonding strength along the c-axis increased and the crystal anisotropy of coefficient of linear expansion decreased, and as a result cracks were prevented. a–b-plane-oriented SNLNs with Lotgering factors of 0.5 to 0.6 were fabricated. These oriented SNLNs with restrained cracks had lower La contents x≥0.05 than randomly oriented SNLNs. The piezoelectric constant of the oriented SNLNs with x=0.05 had d33=95 pC/N, which increased up to 1.5-fold that of randomly oriented SNLNs. It was apparent that the crystal-oriented SNLN ceramics could show restrained cracks and enhanced piezoelectric properties.

Investigation of Miniature Cantilever-Type Ultrasonic Motor Using Lead-free Array-Type Multilayer Piezoelectric Ceramics

We studied the following to clarify the design rule of the miniature cantilever-type ultrasonic motor using lead-free array-type multilayer piezoelectric ceramics, which is (Sr,Ca)2NaNb5O15. The relationship between the motor properties and stator vibrator dimensions was investigated by the finite element method and vibration analysis. The motor properties mainly depended on the cantilever sizes. The motor properties can be especially controlled from the revolution-speed-oriented type to the torque-oriented type by adjusting the vamplate radius of the cantilever. As a result, the design rule was clarified. In accordance with the design rule, the lead-free torque-oriented motor was fabricated and its properties were evaluated. The driving properties of this motor changed to the torque-oriented characteristics, such as the ratio of the maximum torque to the maximum speed was over 1200-fold of that of the motor fabricated in a previous study. It appeared that the driving properties of the lead-free cantilever-type motor can be controlled by using the design rule.

Polarization System and Phase Transition on (Li,Na,K)NbO3 Ceramics

The polarization system and phase transition on Li0.055(Na0.50K0.50)0.945NbO3 (LNKN) ceramics were investigated to determine the piezoelectric properties, relative permittivities and X-ray diffraction (XRD). The piezoelectric properties and relative permittivities were strongly dependent on the poled state, which poling temperatures were 25 or 150 °C. The XRD did not exhibit orthorhombic–tetragonal phase transition around the phase transition temperature because no orthorhombic phase was observed below the phase transition temperature. The LNKN ceramics had multiple poled states, the origin of the multiple poled states was considered to be attributable to the multiple spontaneous polarization (Ps) direction on perovskite structure. From these results, we proposed that the phase transition on LNKN was not an orthorhombic–tetragonal phase transition but a monoclinic-tetragonal phase transition. The monoclinic perovskite structure [Z=1, Pm, a=3.9825(5) A, b=3.9438(4) A, c=4.0217(5) A, β=90.292(3)°] can provide multiple Ps directions, such as [101]pc and [001]pc.

Fabrication of crystal-oriented barium-bismuth titanate ceramics in high magnetic field and subsequent reaction sintering

Abstract High magnetic field was applied to fabricate novel lead-free piezoelectric ceramics with a textured structure. A compact of crystallographically oriented grains was prepared by dry forming in a high magnetic field from a mixed slurry of bismuth titanate and barium titanate powders. Bismuth titanate particles with a size of about 1 μ m were used as the host material. In the forming process, the slurry was poured into a mold and set in a magnetic field of 10 T until completely dried. Bismuth titanate particles were highly oriented in the slurry under the magnetic field. The dried powder compact consisted of highly oriented bismuth titanate particles and randomly oriented barium titanate particles. Barium bismuth titanate ceramics with a- and b-axis orientations were successfully produced from the dried compact by sintering at temperatures above 1100 ° C.

C-axis-Oriented (Sr,Ca)2NaNb5O15 Multilayer Piezoelectric Ceramics Fabricated Using High-Magnetic-Field Method

We formed a c-axis-oriented (Sr,Ca)2NaNb5O15 (SCNN) sheets using a rotation magnetic field, and succeeded in realizing a c-axis-oriented SCNN multilayer piezoelectric ceramic (O-MLPC). The Lotgering factor of both the c-axis-oriented SCNN sheet and inner piezoelectric ceramic of the O-MLPC were approximately 0.80 after sintering. The applied voltage dependences of displacement for both the O-MLPC and a conventional multilayer piezoelectric ceramic (MLPC) with randomly oriented ceramics were examined. As a result, we confirmed that the displacement characteristic of the O-MLPC increased up to a value 2.5 times larger than that of the MLPC.

Properties of Miniature Cantilever-Type Ultrasonic Motor Using Lead-Free Array-Type Multilayer Piezoelectric Ceramics of (Sr,Ca)2NaNb5O15 under High Input Power

The properties of miniature cantilever-type ultrasonic motors using lead-free array-type multilayer piezoelectric ceramics of (Sr,Ca)2NaNb5O15 (SCNN) developed using the design rule were investigated under high input power by comparison with the high-power properties of SCNN ceramics. The frequency dependence of the revolution speed reflected the nonlinear behavior of SCNN ceramics with the hard-spring effect and showed a mirror-reversed image relative to that of the motor of Pb(Zr,Ti)O3 (PZT) ceramics. The output power increased linearly with increasing input power up to 110 mW without heat generation, and the driving properties were almost the same as the expectations under low input power. The output power density characteristics of the motors were high in comparison with those of the commercialized motors of PZT ceramics. It appeared that the motors have a high potential as an environmental friendly piezoelectric device with excellent properties, reflecting the high-power properties of SCNN ceramics.