Yukio Sakabe

Temperature Dependence of Piezoelectric Properties of Grain-Oriented CaBi4Ti4O15 Ceramics.

Piezoelectric properties of grain-oriented bismuth layer structured compound CaBi4Ti4O15 ceramics and their temperature dependencies were studied. The grain-oriented CaBi4Ti4O15 ceramics were fabricated by the templated grain growth method. The highly preferentially (00l) oriented CaBi4Ti4O15 ceramics were obtained and their Lotgering (00l) orientation degree was almost 100%. The electromechanical coupling coefficient of the longitudinal vibration mode (k33) was approximately three times as large as that of the nonoriented specimen, and the temperature coefficient of resonant frequency (|fr-TC|) was the same as that of the nonoriented specimen. The 24 vibration mode is separated from the 15 vibration mode in the thickness shear vibration of the grain-oriented ceramics. The electromechanical coupling coefficient k15 of the grain-oriented specimen was twice as large as k15 of the nonoriented ceramics, while, k24 was one-third that of k15 of the nonoriented specimen. The |fr-TC| of the 15 vibration mode of the grain-oriented specimen was half that of the 15 vibration mode in the nonoriented ceramics, and that of the 24 vibration mode of the oriented specimen was much larger than that of the 15 vibration mode in the nonoriented ceramics.

Effects of Rare-Earth Oxides on the Reliability of X7R Dielectrics

The effects of rare-earth oxides, e.g., La, Nd, Sm, Dy and Yb, on the reliability of multilayer capacitors (MLCs) with X7R dielectrics and Ni electrodes were investigated. Microstructures of the dielectrics were analyzed by transmission electron microscopy (TEM) and electron probe microanalysis (EPMA) in order to characterize the rare-earth ions. Incorporation of rare-earth ions to BaTiO3 ceramics depended on their ionic radius, resulting in different microstructures and electric performances of dielectrics. Dy ions provided BaTiO3 ceramics with ideal X7R characteristics and high reliability. The mechanism governing leakage current was discussed in terms of the voltage dependence of leakage current. Electric properties and related reliability of the capacitors were attributed to solubility, distribution of rare-earth oxides and their occupation site in BaTiO3.

High-Dielectric Constant Ceramics for Base Metal Monolithic Capacitors

In order to make the monolithic ceramic capacitors with a base metal internal electrode, the ceramics of {(Ba1-xCax)O}m{(Ti1-yZry)O2} compositions were investigaed, where 0.02x0.22, 0<y0.20 and 1.005m1.030. These ceramic materials are sintered in an atmosphere of low oxygen to yield a high resistivity (1012 Ω-cm), a high dielectric constant (7,000~9,000), and a low dissipation factor of less than 2.5%. The monolithic capacitors of these ceramics with nickel electrode are as reliable as those with precious metal electode.

Dielectric Properties of Fine-Grained BaTiO3 Ceramics Doped with CaO

Fine-grained dielectric ceramics, i.e., of 0.2 µm grain diameter, were obtained using Ca-doped BaTiO3 powders consisting of particles 0.2 µm in diameter. The (Ba1-xCax)mTiO3 ceramics (x: 0–0.10, m: 1.003–1.009) showed a high dielectric constant and stable temperature dependence, which were provided by interfacial stress due to the grain boundary, even though the ceramics has no core-shell structure. The failure time under an accelerated life condition was remarkably improved with Ca doping, which may be caused by the decrease in BaTiO3 unit volume with Ca2+ at the Ba2+ lattice site, and Ca2+ acceptor ions at the Ti4+ site.

Piezoelectric Properties of Ba and Ca Doped SrBi2Nb2O9 Based Ceramic Materials

The crystalline structure and dielectric and piezoelectric properties of SrBi2Nb2O9 (SBN)-based materials were investigated with the substitution of Ca and Ba ions into the Sr site in this study. X-ray diffraction analysis revealed that these substitutes formed solid solutions throughout the compositions. The Ca substitution increases the ferroelectric transition temperature and maintains the phase transition as that of the normal ferroelectrics, while the Ba substitution lowers the ferroelectric transition temperatures and changes the transition from the normal to the diffuse ferroelectric one. The Ba-substituted SBN shows a smooth elastic anomaly for the Ba substitution of 0.2. A dielectric measurement revealed that the smooth elastic anomaly might be related to small dielectric dispersion characteristics observed around 300°C.

Study of the Valence State of the Manganese Ions in PbTiO3 Ceramics by Means of ESR

ESR measurements have been carried out on Mn ions in PbTiO3 ceramics. Mn ions in the PbTiO3 ceramics are incorporated at Ti4+ sites with mixed valence states of Mn2+ and Mn4+. The proportion of Mn2+ ions is the highest for the calcined powder and changes during the firing process. After the firing it decreases with increasing the firing temperature in the range from 800°C and 1100°C, and increases at temperatures above 1150°C. Additionally, the proportion changes with the amount of Mn ions. The proportion of Mn2+ decreases with increasing Mn dopants up to 0.20 wt%. In the range from 0.20 wt% and 0.25 wt% of MnO2 it increases steeply, and the Mn2+ and Mn4+ ratio is not varied when more than 0.25 wt% MnO2 is doped. Piezoelectric properties of Mn doped PbTiO3 can be explained by the changes of the valence states of Mn ions.

Properties of the Elastic Anomaly in SrBi2Nb2O9-based Ceramics

A study was conducted on the effects of compositional modifications on the temperature coefficient of resonance frequency (TCF) in the disc planar vibration mode for the bismuth layer-structured compound SrBi2Nb2O9 (SBN)-based ceramics. The substitution of the strontium site by divalent and trivalent ions improved the TCF, accompanying the relaxation of elastic anomaly. The tolerance factor, t, was calculated for a pseudo cubic block to study the contribution of the structural factor to Curie temperature, T-C, and the temperature of elastic anomaly, T-ea, for each sample. T-ea showed no apparent tendency with t, whereas T-C increased as t decreased.

Fine-Tolerance Resonator Applications of Bismuth-Layer-Structured Ferroelectric Ceramics

The two-layered SrBi2Nb2O9 (SBN) ceramic resonator that generates second harmonics of the thickness extensional vibration is a strong candidate for fine-tolerance-resonator applications, because of its small electromechanical coupling coefficient and high temperature stability. The Nd substitution of Sr in SBN is effective in further decreasing the temperature coefficient of resonance frequency (TCF) while maintaining its high maximum value of electrical quality factor (Qemax) at a resonance frequency. On the other hand, a grain-oriented SBN-type ceramic resonator has an attractive property of thickness shear vibration. The temperature coefficient of oscillation frequency (TCO) could be less than 10 ppm/°C in an ordinary oscillation circuit with grain-oriented SBN-type ceramics. In this paper, we describe how a fine tolerance resonator can be realized using compositional and structural designs of the bismuth-layer-structured ferroelectric (BLSF) ceramic resonator.

ENERGY TRAPPING CHARACTERISTICS OF BISMUTH LAYER STRUCTURED COMPOUND CABI4TI4O15

Piezoelectric characteristics of bismuth layer structured compound CaBi4Ti4O15 ceramics were studied in terms of the energy trapping phenomenon of the second harmonic thickness extensional (TE2) vibration mode. An electrode-buried-type resonator was prepared by the co-firing technique to generate the TE2 mode, and frequency-lowering-type energy trapping was realized. Favorable resonant characteristics were obtained for piezoelectric filter and oscillator applications with narrow frequency tolerances, which require a small electromechanical coupling coefficient and a high mechanical quality factor. The electromechanical coupling coefficient for the TE2 vibration mode of the resonator was 13.9% and the mechanical quality factor Qm was 2560. The temperature coefficient of the resonance frequency was adequate for the applications. The microstructure of CaBi4Ti4O15 ceramic was also investigated. Marked shape anisotropy of the grain was observed; however, preferential grain orientation was not recognized when the ceramic was prepared by the ordinary firing process.

Preparation and Dielectric Properties of the Multilayer Capacitor with (Ba, Sr)TiO3 Thin Layers by Metalorganic Chemical Vapor Deposition

Barium strontium titanate ((Ba, Sr)TiO 3 ; BST) thin films were prepared on Pt-coated magnesium oxide single-crystal substrates (Pt(111)/MgO(100) and Pt(100)/MgO(100)) at 650°C by metalorganic chemical vapor deposition (MOCVD). The BST films with a perovskite single phase were obtained. Their room-temperature dielectric constant was 400-590 measured at 100 mV and 1 kHz. The leakage current density was below the order of 10 -7 A/cm 2 at 3V, and the breakdown field was above 500 kV/cm. In addition, the multilayer capacitor with five layers of BST was prepared. The room-temperature capacitance with an effective electrode area of 0.16 mm 2 was 20 nF at 100 mV and 1 kHz. The leakage current was on the order of 10 -8 A at 1V, and on order of 10 -5 A at 3 V.