Junichi Kato

Low-Fire Bismuth-Based Dielectric Ceramics for Microwave Use

We have investigated dielectric properties of several bismuth-based ceramics at microwave frequencies. BiNbO4 ceramics containing CuO and V2O5, had a high Q value of Q=4260 (at 4.3 GHz), e=43, and τf=+38 ppm/°C. In the Bi2O3-CaO-Nb2O5 system, Bi18Ca8Nb12O65 composition had a high dielectric constant of e=59, Q=610 (at 3.7 GHz), and τf=+24 ppm/°C. The crystal structure of this composition is considered to be an ordered structure based on the body center tetragonal cell (a=0.377, c=0.542 nm). Furthermore, by substituting Zn for Ca, e increased and τf changed to negative values. In the composition of 45.75BiO3/2-21.75(Ca0.725Zn0.275)O-32.5NbO5/2, excellent properties of e=79, Q=360 (at 3.3 GHz), and τf=+1 ppm/°C were obtained. As all the above ceramics can be sintered below 950°C, they are applicable to multilayer microwave devices with Ag inner conductors.

Dielectric properties of (PbCa)(MeNb)O3 at microwave frequencies

We have investigated the dielectric properties up to microwave frequencies of ceramics represented as (Pb1-xCax)-(MemNb1-m)O3 where Me is selected from Li, Na, Mg, Zn, Ni, Co, Fe, Y, Yb, Al and Cr. High Q values and small temperature coefficients of resonant frequency were obtained in (PbCa)(Mg1/3Nb2/3)O3, (PbCa)(Ni1/3Nb2/3)O3 and (PbCa)-(Fe1/2Nb1/2)O3 with perovskite structure. These dielectric constants and the Q values for a near-zero temperature coefficient are er=73 with Q=1330, er=59 with Q=1700 and er=91 with Q=1650, respectively. The other ceramics with smaller amounts of perovskite phase had degraded characteristics, i.e., low Q values or large temperature coefficients. In lead- and calcium-based perovskite, it seems that the high dielectric constant occurs due to Pb content in A-sites and smaller average ion radius in B-sites.

Dielectric Properties of Pb-Based Perovskite Substituted by Ti for B-site at Microwave Frequencies

Substitutions of B-sites by Ti in several Pb-based perovskite ceramics that had high relative permittivities (er), high Q values, and small temperature coefficients of resonant frequency (τf) were studied in order to control er and τf independently. It was found that relative permittivities with near-zero τf in (Pb, Ca)(Zr, Ti)O3, (Pb, Ca){(Fe1/2Nb1/2), Ti}O3, and (Pb, Ca){(Mg1/3Nb2/3), Ti}O3 systems could be controlled in the er regions lower than 105, 95, and 70, respectively. All these systems had sufficiently high Q values. They are applicable to resonant devices for mobile communications.

Dielectric properties of lead alkaline-earth zirconate at microwave frequencies

Dielectric properties of alkaline-earth-substituted PbZrO3 ceramics up to microwave frequencies were investigated. Although there were no preferable characteristics in the Ba- or Sr-substituted system, the ceramics in a (PbCa)ZrO3 system showed not only high dielectric constants in the range of 100 to 118, but also high Q values of 1000 to 1150 and small temperature coefficients of resonant frequency of 0 to 30 ppm/ °C. The crystal structure of the Ca-substituted ceramics was also investigated by X-ray powder diffraction. The structure changed from PbZrO3-type orthorhombic to CaZrO3-type orthorhombic through cubic and rhombohedral with increasing Ca substitution. Coaxial dielectric resonators made of the selected above material had Q values in the range of 430 to 450 at the 900 MHz band.

Endurance against moisture for protonic conductors of perovskite-type ceramics and preparation of practical conductors

Abstract Aimed at developing practical protonic conductors with high reliability and conductivity, we initially investigated endurance against moisture for various protonic conductors of perovskite-type ceramics by placing samples in boiling water and in steam. Endurance against moisture involves the density and homogeneity of the sinters. Compounds containing Ce were affected by moisture and compounds containing Zr were hardly affected. Consequently, protonic conductors that have practical durability against moisture and high conductivity, such as BaZr 0.6 Ce 0.2 Gd 0.2 O 3 and BaZr 0.4 Ce 0.4 In 0.2 O 3 , were prepared.

Some Solid Solutions of the A5B10O30- and A6B10O30-Type Tungsten-Bronze Ferroelectrics

The phase relations of several A5B10O30- and A6B10O30-type solid solutions were determined, where A=Ba, Pb, Sr, Ca, Na and K, and B=Nb and Ta. The tungsten-bronze(TB)phase was observed in a wide range of the A5B10O30-type niobates, though the end components for A=Ba, Sr, Ca are not of the TB structure. Substitution of Ta for Nb stabilizes the TB structure in the A5B10O30-type systems. Introduction of Na or K on the A site, which causes the compositional variation from A5B10O30- to A6B10O30-type, enhances the TB stability. The systems between A5B10O30 and A6B10O30 are almost entirely soluble in the TB structure. The ferroelectric strength follows the order Pb>Ba>Sr>Ca for the divalent A ion, 0>Na>K for the monovalent A ion (presumably in 12-coordinated site), and Nb

Measurement of surface shape and deformation by phase-shifting image digital holography

Surface shape and deformation measurement by phase-shifting digital holography using an imaging setup is presented. The differences of the reconstructed phases before and after tilt of the illumination beams and object deformation provide the contour lines of the surface height and deformation, respectively. Suppression of speckle noise and comparisons between experiments and calculation are discussed.

Electron Charge Density Study of (Na1-xKx)NbO3 in Cubic Structure

The electron charge density study by synchrotron-radiation powder diffraction has been performed for the cubic structure of (Na1-xKx)NbO3 (NKN: 0≤x≤1) at 1000 K to investigate the atomic substitution effect on chemical bonding. Our precise analysis using the maximum entropy method (MEM)/Rietveld method demonstrates that the covalent bonding is formed on the Nb–O bond whereas the Na/K atoms are ionic in the entire composition range. The thermal motion of the Na ion in NaNbO3 is fairly larger than that of the K ion in KNbO3. The charge density distributions around the O atoms in NaNbO3 are extended in the directions perpendicular to the Nb–O bond, which can be related to the rotational mode of the Nb–O6 octahedron driving the antiferroic phase transition. No such anisotropy is clearly observed in KNbO3 around the O atoms. These behaviors are closely related to the change in the tolerance of the perovskite structure caused by the atomic substitution.

Maltilayer Ceramic Capacitor with Copper Electrode

Dielectric material of (PbaCab){(Mg1/3Nb2/3)Ti(Ni1/2W1/2)}O2+a+b, where a+b>1, has been investigated. This composition has been proved to be fired under low oxygen partial pressure of less than 10-1 Pa with high resistivity. To make multilayer ceramic capacitor, the dielectric material was co-fired with copper electrode in an atmosphere of intermediate oxygen pressure. The obtained capacitor met to Z5U specification and had low dissipation factor and small change of capacitance under a d.c. bias voltage.

Crystal Structure Refinement of (Pb1-xCax)ZrO3 by the Rietvelt Method

Superlattice structures in rhombohedral perovskite (Pb 1-x Ca x )ZrO 3 , which has high dielectric constant with small temperature coefficient and high Q value at microwave frequencies, were refined by the X-ray Rietvelt powder profile analysis. The superlattice structure is caused by slight displacement of lead and zirconium ions from the ideal perovskite sites, together with twisting and deformation of oxygen octahedra. The Q value of (PbCa)ZrO 3 at microwave frequencies has no relation to the formation of the superlattice structures, as indicated by the absence of cation ordering