Showing papers by "Yuji Hiruma published in 2010"

Electric-field-induced strain for (Bi1/2Na1/2)TiO3-based lead-free multilayer actuator

Abstract: Multilayer prototype actuators were demonstrated using (Bi1/2Na1/2)TiO3 [BNT]-based ceramics as active layers and Pt as internal electrodes. One of the BNT-based solid solutions, 0.68(Bi1/2Na1/2)TiO3–0.04(Bi1/2Li1/2)TiO3–0.28(Bi1/2K1/2)TiO3 (BNLKT4–28) has been selected as the an active layer and it showed a relatively large piezoelectric strain constant d33 of 130 pC/N and a high depolarization temperature Td of 226°C. The total number of layers was 10 and the active layer thickness was 125 µm for the sintered body. The final compact dimensions were approximately 5 × 5 × 2 mm3. From the SEM observation, there were no apparent delaminations around the interface between Pt electrodes and active BNLKT layers. The large electric-field-induced strain at 70 kV/cm was 0.17% and the longitudinal dynamic displacement at the same electric field was 2.1 µm.

Fabrication and Piezoelectric Properties of Textured (Bi1/2K1/2)TiO3 Ferroelectric Ceramics

Abstract: Textured (Bi1/2K1/2)TiO3 (BKT) ceramics were prepared by a reactive templated grain growth (RTGG) method to improve their piezoelectric properties. Also, a hot-pressing (HP) method was modified on the basis of RTGG method to obtain dense ceramics and promote the grain orientation. The textured BKT ceramics prepared by the RTGG and HP methods exhibited a relatively high orientation factor F of 0.82 and a high density ratio of 95–99%. Scanning electron microscopy (SEM) micrographs of the textured HP-BKT indicated a textured and poreless microstructure. In addition, the resistivity of the textured HP-BKT was 1.73×1013 Ωcm. The piezoelectric strain constant d33 determined by means of resonance and antiresonance method was 125 pC/N for the direction parallel to the sheet-stacking direction of the RTGG process. From the measurement of field-induced stain, the normalized d33* (=Smax/Emax) at 80 kV/cm were 127 and 238 pm/V on the randomly oriented and textured samples (F=0.82) for the (∥) direction, respectively.

High-Power Piezoelectric Characteristics of Bi4Ti3O12–SrBi4Ti4O15-Based Ferroelectric Ceramics

Abstract: The high-power piezoelectric characteristics of lead-free piezoelectric ceramics based on a mixed bismuth layer-structured ferroelectric, Bi4Ti3O12–SrBi4Ti4O15 (abbreviated as BIT–SBTi) were studied. In addition, MnCO3-doped BIT–SBTi (abbreviated as BIT–SBTi + Mn x wt %) were prepared to improve their high-power piezoelectric properties such as the mechanical quality factor Qm. In the case of pure BIT–SBTi, its vibration velocity v0–p at 5 V/mm field is 1.5 m/s. The v0–p values of the BIT–SBTi + Mn 0.2 and 0.4 wt % ceramics were above 2.0 m/s at 5 V/mm. Also, we observed that the mechanical quality factor Qm at a large amplitude of BIT–SBTi + Mn 0.4 wt % was maintained higher than 4000 at v0–p of 2.0 m/s. The high-power characteristics of BIT–SBTi + Mn x wt % were superior to those of hard Pb(Zr,Ti)O3 (abbreviated as PZT) at a vibration velocity v0–p>1.0 m/s. Therefore, Mn-doped BIT–SBTi-based ceramics are a promising candidate for lead-free high-power applications.

Depolarization Temperatures and Piezoelectric Properties of (Bi0.5Na0.5)TiO3 Ceramics and Single Crystal

Abstract: The phase transition temperatures and piezoelectric properties of (Bi0.5Na0.5)TiO3 (BNT) ceramics and single crystal were investigated. This study revealed that the high conductivity of BNT ceramics is attributed to the Bi vaporization during sinterint. The highest depolarization temperature T d of 187°C was obtained for the stoichiometric BNT ceramics, and T d tends to decrease as the composition deviates from stoichiometric BNT. T d of BNT single crystal was 158°C because of Na poor composition. BNT ceramics was easy to pole fully when the Bi/Na ratio is more than 1.0. The electromechanical coupling factor k 33 and piezoelectric properties d 33 of fully poled stoichiometric BNT ceramics were 0.459 and 72.9 pC/N, respectively.

Local Structure of Li-Substituted (Bi0.5Na0.5)TiO3

Abstract: The local structure analysis of Li-substituted (Bi0.5Na0.5)TiO3 was carried out by a synchrotron radiation X-ray pair-distribution function (PDF) method. The PDF peak is resolved as a doublet owing to the presence of two phases with distinct local structures, namely, the rhombohedral and tetragonal phases. The coexisting local structure is very similar to the orthorhombic structure. A martensitic phase transformation occurred at the deporalization temperature (Td) because of the similarity of the local structures.

Piezoelectric Properties of (Bi0.5Na0.5)TiO3-Based Solid Solution at Large-Amplitude Vibration

Abstract: The high-power piezoelectric characteristics of (Bi0.5Na0.5)TiO3 based solid solution ceramics, x(Bi0.5Na0.5)TiO3-y(Bi0.5Li0.5)TiO3-zBaTiO3 + MnCO3 w wt% [x + y + z = 1, y = 0.04, z = 0.02–0.08, BNLBT4-100z + Mnw], were focused on under large-amplitude vibration in this study. The BNLBT4-100z system has a morphotropic phase boundary (MPB) at approximately z = 0.06, and BNLBT4-2 and BNLBT4-4 exhibited rhombohedral symmetry, whereas BNLBT-4-8 exhibited tetragonal symmetry. The piezoelectric strain constant, d 33, for the MPB composition (z = 0.06) under small-amplitude vibration was the largest (>40 pC/N) among all compositions and the mechanical quality factor, Q m, of the composition with rhombohedral symmetry was higher than those of compositions with other symmetries. The vibration velocity, which was measured using a laser Doppler vibrometer reached 2 m/s for BNLBT4-2+Mn0.4 and BNLBT4-4+Mn0.4 rhombohedral symmetry and BNLBT4-6+Mn0.4 with the MPB, as compared with 1 m/s for BNLBT4-8+Mn0.4 with tetragona...

High Power Piezoelectric Characteristics for Perovskite-Type Lead-Free Ferroelectric Ceramics

Abstract: High power piezoelectric characteristics of perovskite-type lead-free ferroelectric ceramics, 0.88(Bi0.5Na0.5) TiO3-0.04(Bi0.5Li0.5)TiO3-0.08(Bi0.5Na0.5)TiO3 + MnCO3 0.4 wt% [BNLKT4-8Mn0.4] and KNbO3 + MnCO3 0.8 wt% [KN-Mn0.8], were focused on under large-amplitude vibration as compared with those of Pb(Zr,Ti)O3 [PZT]-based ceramics. The maximum vibration velocities, v o-p for BNLKT4-8Mn0.4 and KN-Mn0.8 reached larger than 2 m/s. A mechanical quality factor, Qm, at large-amplitude vibration for all compositions including PZT-based ceramics decreased with increasing the v o-p. The Qms of BNLKT and KN ceramics were smaller than that of hard PZT [N6] at the small-amplitude vibration. However, at the large amplitude vibration level of v o-p > 0.6 m/s, Qm values of BNLKT and KN are larger than that of N6. Therefore, lead–free piezoelectric ceramics such as BNLKT-Mn0.4 and KN-Mn08 possess superior mechanical stability at large-amplitude vibration. This is very good sign for high power piezoelectric applications.

Vibration velocities under high-power driving on perovskite-type lead-free ferroelectric ceramics

Abstract: High power piezoelectric characteristics of perovskite-type lead-free ferroelectric ceramics, 0.88(Bi 0.5 Na 0.5 )TiO 3 -0.04(Bi 0.5 Li 0.5 )TiO 3 -0.08(Bi 0.5 Na 0.5 )TiO 3 +MnCO 3 0.4 wt% [BNLKT4-8Mn0.4] and KNbO 3 +MnCO 3 0.8 wt% [KN-Mn0.8], were focused on under large-amplitude vibration as compared with those of Pb(Zr,Ti)O 3 [PZT]-based ceramics. The maximum vibration velocities, v o-p for BNLKT4-8Mn0.4 and KN-Mn0.8 reached larger than 2 m/s. A mechanical quality factor, Q m , at large-amplitude vibration for all compositions including PZT-based ceramics decreased with increasing the v o-p . At the large amplitude vibration level of v o-p >0.6 m/s, Q m values of BNLKT and KN are larger than that of N6. Additionally, heat generation under a continuous driving on lead-free and hard PZT [N-6] ceramics show similar tendency as a function of vibration velocity.

Effect of Dopant, Crystal Orientation, and Space Charge Layer on Oxygen Diffusion in Bi4Ti3O12 Ceramics

Abstract: We studied oxygen diffusion in non- and Nb2O5-doped Bi4Ti3O12 (BIT) ceramics by two-dimensional isotope mapping. In non-doped BIT, the grain boundary acted as a barrier to oxygen diffusion, reflecting the presence of a space charge layer at the grain boundary. In Nb2O5-doped BIT, a textured morphology was found by bulk and grain-boundary diffusion of oxygen. Diffusion coefficients were determined from the individual grains and grain boundaries. The difference in diffusion paths resulted from the decrease in oxygen-defect concentration owing to the addition of Nb2O5. The bulk-diffusion coefficient along the ab-plane was about one order of magnitude larger than that in the direction of the c-axis. The grain-boundary-diffusion coefficients varied by about two orders of magnitude. The bulk and grain-boundary diffusion of oxygen depended significantly on the crystal orientation.

Fabrication and Microstructure of Grain-Oriented (Bi1/2K1/2)TiO3 Ceramics

Abstract: Grain-oriented (Bi1/2K1/2)TiO3 (BKT) ceramics were prepared by the reactive templated grain growth (RTGG) method, and a hot-pressing (HP) method was modified on the basis of the RTGG method to obtain dense ceramics. The BKT ceramic sintered at 1060°C showed a single-phase perovskite structure. The grain-oriented BKT prepared by the HP method exhibited a relatively high orientation factor F of 0.82 and a high density ratio of 99%. SEM micrographs of the HP-grain-oriented BKT indicated a textured and poreless microstructure. On the basis of the density ratio of 87% for the grain-oriented BKT without HP, the HP method was considered very effective for improving the density ratio even for the RTGG sample. In addition, the resistivity of the HP-grain-oriented BKT was 1.73 x 1013 •cm.

Temperature Dependences of Piezoelectric Properties of Grain-Oriented SrBi2Nb2O9-Bi4Ti3O12 Ceramics

Abstract: Bismuth layer-structured ferroelectrics (BLSFs) have been studied for resonator applications due to its low-temperature coefficient of resonance frequency (TC-f). To control the TC-f to lower, an use of the phase transition is demonstrated in which a mixed-bismuth layer structure of SrBi2Nb2O9-Bi4Ti3O12 (SBN-BIT) is focused on as the new approach. Thus, the TC-f was tried to be controlled by using the phase transition of the SBN-BIT system. The electrical properties and the temperature dependences of the piezoelectric properties were investigated for the proposed system. The temperature dependence of resonance frequency indicated that TC-f changed from −74.8 to −14.6 ppm/°C for non oriented samples and from −42.6 to +75.8 ppm/°C for oriented samples after undergoing the phase transition.