Takeo Tsukada

Piezoelectric Properties of SrBi4Ti4O15-Based Ceramics

Piezoelectric properties of lead-free bismuth layer structure oxide, SrBi4Ti4O15 (SBT) based ceramics, were studied. By means of La substitution and Mn addition, the maximum value of Q (Qmax ) between resonant frequency and anti-resonant frequency was larger than that of SBT. These materials could be utilized in practical applications as substitutes for lead titanate based ceramics (PT) and lead zirconate titanate based ceramics (PZT) which are used mainly in resonators. The reason for the higher Qmax value was identified by microstructual analysis as being due to the absence of a defect structure.

Piezoelectric Properties of Bi3TiNbO9-BaBi2Nb2O9 Ceramics.

Piezoelectric properties of lead-free bismuth layer structure oxides, (1-x)Bi3TiNbO9 (BTN)–xBaBi2Nb2O9 (BBN) (m=2) ceramics, have been studied. We have observed large piezoelectric properties for x values between 0.1 and 0.3. Within this range of x values, these specimens have an orthorhombic structure, high anisotropy of the a and b axes and high resistivity. Also, for these samples, a large coercive force (Ec) of 8.0 kV/mm, large remanent polarization (Pr) of 7.1 µC/cm2 at 200°C and high Curie temperatures (Tc) of 700–900°C have been obtained. Maximum mechanical quality factor (Qm) of 9000 at 16 MHz thickness extensional third vibration mode (TE3rd) has been measured.

Thickness-Shear Vibration Mode Characteristics of SrBi4Ti4O15-Based Ceramics

Dielectric and piezoelectric properties have been investigated in bismuth layer-structure compounds SrBi4Ti4O15 (SBT) and BaBi4Ti4O15 (BBT)-based solid solutions. Lanthanum-substituted and manganese-added SBT and BBT form solid solutions for all levels of Ba substitution. The Curie temperature and coercive field strength decrease monotonously with the amount of Ba substitution. The mechanical quality factor, Qm, of the thickness-shear vibration mode also decreases. The value of elastic compliance increases with the amount of Ba substitution, but conversely its temperature dependency decreases.

Thermal Reliability of Alkaline Niobate-Based Lead-Free Piezoelectric Ceramics

Alkaline niobate-based (K,Na,Li,Ba,Sr)(Nb,Ta,Zr)O3 (ANSZ) ceramics were prepared by conventional sintering process, and their piezoelectric properties were measured. The Curie temperature (TC) of the ANSZ ceramic was 278 °C. The electromechanical coupling factor (kp) and the piezoelectric constant (d33) were 45.5% and 295 pC/N, respectively, and the dielectric permittivity (e33T/e0) was 1610 at room temperature. The thermal reliability was tested by 1000 cycles of thermal shock with temperatures ranging from -55 to 125 °C. The change in d33 of ANSZ was compared with that of commercial Pb(Zr,Ti)O3 after 1000 cycles of thermal shock. The phase transition behavior of ANSZ was investigated by X-ray diffraction (XRD) and differential scanning calorimetry (DSC) simultaneous measurement. No appreciable endothermic peak accompanied by a polymorphic phase transition was observed on the DSC curve. The crystalline structure was investigated in detail by XRD measurement with high-energy synchrotron radiation. The coexistence of two ferroelectric phases in a wide temperature range (from -175 to 150 °C) was observed.

Poling Field Dependence of Piezoelectric Properties and Hysteresis Loops of Polarization versus Electric Field in Alkali Niobate Ceramics

The DC poling field dependence of piezoelectricity was investigated to evaluate the mechanism of domain alignment in lead-free ceramics of the form of (1-x)(Na,K,Li,Ba)(Nb0.9Ta0.1)O3–xSrZrO3 (x=0–0.07) by comparison with those of Pb(Zr,Ti)O3 (PZT), PbTiO3 (PT), and BaTiO3 (BT) ceramics. Poling was conducted at 150 °C for 30 min while varying the poling field (E) between ±4.0 kV/mm. By increasing x from 0 to 0.07, the relative dielectric constant (er), electromechanical coupling factor in the planar mode (kp), frequency constant in the kp mode (fcp), and piezoelectric strain constant (d33) vs E plots showed domain clamping at a specific E. E was the coercive field estimated from the DC poling field dependence. The changes in er, kp, fcp, and d33 with E became smaller at x=0.06–0.07, because of the proximity to the paraelectric phase. The ceramics with x=0, such as PT or BT ceramics, show similar er, kp, fcp, and d33 vs E plots. The maximum kp (48%) and d33 (307 pC/N) were obtained for x=0.05 with the lowest fcp of 2964 Hzm, as shown in the er, kp, fcp, and d33 vs E plots for ceramics such as tetragonal hard PZT ceramics. Since domain alignment in the ceramics was accompanied by the deformation of crystals as a result of applying the poling field, it was clarified that the lead-free ceramics must have a high kp and high d33 to realize a low fcp, which corresponds to a low Youngs modulus. In addition, the optimal ceramic composition was obtained in the typical domain-clamping state from the poling field dependence. Furthermore, it was found that a higher kp was realized at a larger remnant polarization and a smaller coercive field in a symmetrical hysteresis loop of polarization vs electric field (P–E hysteresis loop), because of the easy alignment of ferroelectric domains by applying a poling field. The results of the poling field dependence were also supported by results of expansion strain measurement.

High Power Characteristics of (Ca,Ba)TiO3 Piezoelectric Ceramics with High Mechanical Quality Factor

(Ca0.1Ba0.9)TiO3 + x wt % MnCO3 [x=0, 0.2, 0.5, 1.0] (CBT-Mx) ceramics were prepared by conventional sintering, and their dielectric and piezoelectric properties were measured. The mechanical quality factor (Qm) of CBT was markedly enhanced by Mn addition and reached 2400 when x=0.5. The dielectric loss tangent (tan δ) was 0.0023 at room temperature. The Curie temperature (TC) was 133 °C. Then, the high power characteristics of CBT-M0.5 were investigated. The maximum vibration velocity (v0) of CBT-M0.5 was 1.1 m/s and was higher than that of Pb(Zr,Ti)O3-based ceramics (Hard-PZT). The heat generation of CBT-M0.5 was smaller than that of Hard-PZT at the same v0. The resonant frequency (fr) of CBT-M0.5 was stable up to v0 of 1.1 m/s. Additionally, the temperature stability of fr was investigated in the practical application temperature range (from -20 to 80 °C). The amount of change in fr for CBT-M0.5 was larger than that for Hard-PZT below 10 °C.

Poling Field Dependence of Ferroelectric Properties in Alkali Bismuth Titanate Lead-Free Ceramics

The DC poling field dependence of ferroelectric properties was investigated to evaluate the mechanism of domain alignment in lead-free ceramics of the forms of (1-x)(Na0.5Bi0.5)TiO3–x(K0.5Bi0.5)TiO3 (x=0.08–0.28), 0.79(Na0.5Bi0.5)TiO3–0.20(K0.5Bi0.5)TiO3–0.01Bi(Fe0.5Ti0.5)O3 and (1-x)(Na0.5Bi0.5)TiO3–xBaTiO3 (x=0.03–0.11). From the DC poling field (E) dependence of ferroelectric properties, asymmetrical shapes in piezoelectric constants vs ±E caused by nonuniform mobility of domain alignment in the application of positive and negative poling fields were observed in the small amount substitution by (K0.5Bi0.5)TiO3 (x0.11) and BaTiO3 (x0.03). On the other hand, symmetrical shapes in piezoelectric constants vs ±E were observed in higher piezoelectricity with lower frequency constant accompanied with typical domain clamping. The effects to improve ferroelectric properties by Bi(Fe0.5Ti0.5)O3 and by BaTiO3 substitutions for (Na0.5Bi0.5)TiO3 were also proved by the measurement of P–E hysteresis loops.

High Coercive Force of Substituted SrFe12-aMaO19 (M=Al, Cr) Ferrite Particles

The effects of the substitution of Al or Cr into Sr-ferrite powder on the Curie temperature (Tc), saturation magnetization (σs) and coercive force (Hc) were studied for SrFe12-aMaO19 (M=Al, Cr; a=3, 4, 5). With increasing substitution content, both Tc and σs decrease, while Hc increases drastically. We obtained a high Hc of 13.0kOe for SrO5.8Fe7/6Al5/6O3.

Grain Size Dependence of the Microstructure and Dielectric Properties of Potassium Niobate-Barium Titanate Ceramics

In this study, 0.8 KNbO3 (KN) -0.2 BaTiO3 (BT) ceramics were prepared using KN powder with the diameter of 100 nm and BT powders with the diameter of 100, 300, or 500 nm. The relative densities were more than 96 % of the theoretical densities of the samples. The dielectric constant of the samples was temperature-stable at temperatures between-50 and 300 °C and it was found that the dielectric constant of the 0.8KN-0.2BT ceramics increased as the BT diameter increased.

Preparation of Potassium Niobate–Barium Titanate Ceramics Using Well-Dispersed Nanoparticles and their Dielectric Properties

ANbO3 – BaTiO3 (A=K, Na, or K0.5Na0.5) system ceramics were prepared using a conventional sintering method, and their dielectric properties were investigated. It was found that the dielectric constant of KNbO3-BaTiO3 and (K0.5Na0.5) NbO3- BaTiO3 system ceramics did not strongly depend on temperature between 20 and 400 °C, making them useful for capacitor application.