Ichiro Ueda

Electromechanical Properties of PbTiO3 Ceramics Containing La and Mn

A piezoelectric ceramic material having low dielectric constant, high thickness coupling factor, high mechanical quality factor, high stability, and high operating temperature, has been prepared from PbTiO3 incorporated with 2.5 mol% of LaO12 and 1.0 mol% of MnO2. Typical electromechanical constants of this material are as follows: dielectric constant e11T/e0u2009230,u2009e33T/e0u2009170; coupling factor k33 0.46, kt 0.46, k15 0.28, kp 0.07, k31 0.04; mechanical quality factor Q 1100, Poissons ratio σE 0.20. Frequency constants Nt and N3t of the fundamental and third‐harmonic thickness vibrations have temperature coefficients of −1.1 × 10−4°C−1 and −2 × 10−5°C−1, respectively. Aging rates of Nt and N3t, are +0.02% and −0.02%/time decade at 30°C, respectively. The Curie point of this material exists at 470°C, and k33 and kt increase gradually with temperature up to 400°C. This material has grain size of 2–3 μ and bending strength of 2 × 107 kg/m2, and can be polished into very thin plate. The PbTiO3 ceramics have a h...

Piezoelectricity in Ceramics of Ferroelectric Bismuth Compound with Layer Structure

Piezoelectric properties have been studied on ferroelectric ceramics comprising bismuth compounds with layer structure, PbBi2Nb2O9, PbBi4Ti4O15, SrBi4Ti4O15 and Na0.5Bi4.5Ti4O15. These ceramics have the high mechanical quality factor Q(2000~7200), low aging rate of frequency constant Nt(30~60 ppm/time decade), low temperature coefficients both of Nt(-50 ppm/°C) and of coupling factor kt(70 ppm/°C), low Poissons ratio σ(0.23~0.27), and large anisotropy in coupling factor. A small value of kt in these ceramics probably relates to two-dimensional restriction on permissible rotation of the spontaneous polarization. The poling characteristics in the ceramics can be improved by some additives. Grain boundaries in these ceramics are of nearly rectangular shape, and an etch pattern of fine stripes appears always in parallel to the length of the boundary.

Piezoelectric Properties of Modified PbTiO3 Ceramics

PbTiO3 ceramics with high density and high resistivity have been prepared by adding less than 5 mol % of Bi2/3TiO3, PbZn1/3Nb2/3O3 or their derivatives. These ceramics have dielectric constants of about 200, and can be poled at 200°C under a d. c. field of 40 to 70 kV/cm. The piezoelectric coupling factors k15, k33 and k31 amount to 0.43, 0.35 and 0.068, respectively. The value of k33 is nearly constant up to the Curie temperature of about 500°C. The aging rate of frequency constant does not exceed 0.1%/time decade. The present ceramics can be used as stable piezoelectric elements in high temperature and high frequency.

Mechanism of Aging in Polycrystalline BaTiO3

Microscopic observation of the domain structure in polycrystalline BaTiO 3 is carried out. After the specimen is cooled down to room temperature through the Curie point the domain structure changes gradually from an initial irregular one to a final one consisting of fine stripes of 90°-domains. Such a change is named “90°-splitting.” The aging of dielectric constant may be due to an increase in clamping effect by the 90°-splitting. This “90°-splitting model” may explain also the agings in dielectric loss and hysteresis loop. The dielectric constant decreases linearly with logarithm of aging time. It was shown theoretically that the displacement of a 90°-wall towards the mechanically most stable position is proportional to the logarithm of time in the case of whisker crystal. The “logarithmic time dependence” of dielectric constant in polycrystalline specimen may be explained as due to the 90°-splitting which progresses at a rate proportional to logarithm of time.

Effects of Additives on Piezoelectric and Related Properties of PbTiO3 Ceramics

Effects of additives Li2CO3, Ag2O, NiO, Cr2O3, Fe2O3, Gd2O3, Bi2O3, TiO2, MnO2, Nb3O5 and WO3 on piezoelectric and related properties of PbTiO3 ceramics are studied. Additives partly dissolve in lattice and the rest segregate at grain boundary. These additives act as grain growth inhibitors and binders. Additions of Li2CO3, NiO, Fe2O3 and MnO2 are most effective for densification. The additives Gd2O3, Bi2O3, Nb2O5 and WO3 give high resistivity probably by compensating Pb vacancies. Many piezoelectric and related properties depend on species and content of additives. Grain size is a main factor influencing these properties. The specimens with Cr2O3 and MnO2 characterized by coarse grain have small e*, small dissipation factor, short poling time, large coupling factors, high mechanical Q and small elastic compliance. These features may be explained by diminishing of stress between grains, decrease of interfacial polarization and large binding force at grain boundary.

Semiconductive Single Crystal of BaTiO3Reduced in Hydrogen Atmosphere

The electrical resistivity, optical transmission, effects of chemical etching, Hall effect, thermoelectric force and electron spin resonance have been studied on single crystals of BaTiO 8 reduced for five hours at temperatures from 400 to 1000°C in a hydrogen atmosphere. The reduction treatment causes a lowering of the resistivity, and enhancement of the infrared absorption centered at 2.3µ and a visible absorption near the optical absorption edge. The single crystals are not always reduced homogeneously. The resistivity of a homogeneously reduced crystal changes abruptly at the three transition temperatures. The sign of the Hall coefficient and the thermoelectric power indicates that the charge carriers in the reduced crystals are electrons. On the basis of the results obtained, a tentative model is proposed for defects in the reduced single crystal.

Frequency spectra of resonant vibration in disk plates of PbTiO3 piezoelectric ceramics

The frequency spectra of resonant vibration in disk plates of PbTiO3 piezoelectric ceramics were observed for diameter to thickness ratio (r) of 5 to 30 near the fundamental thickness extensional mode. The observed spectra could be classified into three groups of thickness mode and two groups of radial mode. For comparison, theoretical spectra for isotropic disk plate were also calculated for various Poissons ratios (σ) of disk material on the basis of Gazis and Mindlins theory. The calculations showed that the theoretical radial mode spectra can be divided into a strongly σ‐dependent group and a slightly dependent one, and also showed that the upper ends of terrace‐type spectra appear as a straight line at the cutoff frequency in a large‐r region and may be corresponded to the thickness extensional mode. In fact, the fitting of the upper‐end spectra to the experimental thickness extensional mode by adjusting σ, gives not only qualitative agreement of all experimental spectra with the theoretical ones, ...

Oxidation Phenomena in Semiconducting BaTiO3

The effects of sintering ambient and cooling procedure on the electrical resistivity of Gd-doped polycrystalline BaTiO 3 have been investigated. Effects of thermal annealing in air on the resistivity-temperature characteristic have been also studied, of Gd-doped specimens as well as reduced BaTiO 3 both in polycrystalline and single crystal forms. The specimens sintered in nitrogen or those sintered and followed by quenching in air have been found to be semiconducting in a wide range of Gd content (0.2∼1.0 atomic %). The high resistivity of highly doped specimens, obtained by the usual sintering process, results from the oxidation during cooling in air. The resistivity anomaly at the Curie point of some reduced single crystals is shown to be surface effect. The PTC anomaly of resistivity in polycrystalline materials may be due to oxidized grain boundary. The oxygen partial pressure during cooling is more effective for the PTC anomaly than that during sintering.

Dielectric Breakdown of Polycrystalline BaTiO3

The temperature dependence of breakdown field, distribution of time lag. and dielectric constant in high electric field were studied on polycrystalline BaTiO 3 . The d. c. breakdown field is nearly constant in the temperature range 20 to 150°C, on the other band the pulse breakdown field changes markedly near the Curie temperature (120°C). The time lag is statistical and depends on the applied field. The “total” dielectric constant in high fields behaves differently from that in low fields, that is higher in ferroelectric state than in paraelectric state, decreasing remarkably near the Curie temperature. From these facts, it is concluded that the breakdown is of the avalanche type. It is suggested that the pulse breakdown field ralates to the high field dielectric constant and the d. c. breakdown field is affected by the transport of free charge.