Masaru Yokosuka

Electrical and electromechanical properties of hot-pressed Pb(Fe1/2Nb1/2)O3 ferroelectric ceramics

Dense ceramics of Pb(Fe1/2Nb1/2)O3 with high resistivity were fabricated below 1000°C by making use of the hot-pressing technique. For these hot-pressed specimens, measurements of the spontaneous polarization, dielectric constants, electromechanical coupling factors, piezoelectric constants and elastic compliance constants were carried out as a function of temperatures between -30°C and 200°C. Temperature variations of the resistivity and linear thermal expansion were also studied. At room temperature, the following values were obtained: e33T/e0=2640, Ps=11.3 µC/cm2, k33=0.266, d33=145×10-12 C/N and s33E=12.3×10-12 m2/N. These values were briefly compared with those of BaTiO3 ceramics.

Dielectric Dispersion of the Complex Perovskite Oxide Ba(Fe1/2Nb1/2)O3 at Low Frequencies.

Ceramic specimens of the complex perovskite oxide Ba(Fe1/2Nb1/2)O3 were fabricated by conventional solid state sintering. Dielectric constants were measured as a function of temperature as well as of frequency. As a result, dielectric constants showed an unusual temperature dependence. Moreover, a large dielectric dispersion was observed below 1 MHz, and it was represented by the Cole-Cole circular arc law. The present dielectric dispersion was interpreted on the basis of the interfacial polarization at the grain boundary region.

Dielectric and piezoelectric properties of mn-modified Bi4CaTi4O15 based ceramics

Solid solution ceramics of the Bi4SrxMnyCa1-(x+y)Ti4O15 system were synthesized by the conventional ceramic process. Measurements of dielectric, electromechanical and piezoelectric properties were conducted as a function of both composition and temperature. As a result, it was found that piezoelectric properties are greatly improved as the appropriate amount of Mn ion is introduced into the Ca ion-site. Maximum values obtained are as follows: electromechanical coupling factor kP=0.064, piezoelectric constant d33=21 pC/N for the composition with x=0.5 and y=0.1 (Bi4Sr0.5Mn0.1Ca0.4Ti4O15), and the mechanical quality factor Qm=3250 for the composition with x=0.5 and y=0.05 (Bi4Sr0.5Mn0.05Ca0.45Ti4O15). Piezoelectric constant d33 was found to take nearly the same value of 20 pC/N over the range of x=0.4 to 0.9 for the fixed y of 0.1.

Electrical, Electromechanical and Structural Studies on Solid Solution Ceramic Pb(Fe1/2Nb1/2)O3?Pb(Zn1/3Nb2/3)O3

Binary solid solutions of the system xPb(Fe1/2Nb1/2)O3–(1-x) Pb(Zn1/3Nb2/3)O3 were synthesized by the conventional ceramic process, where the constituent Pb(Zn1/3Nb2/3)O3 ceramic is not ferroelectric, having a pyrochlore structure. For highly dense ceramic specimens with varying compositions, various physical properties were investigated. As a result, structural conversion from the pyrochlore to the perovskite phase was found to occur in the range of x>0.1. Properties such as dielectric constant and remanent polarization also exhibited anomalies corresponding to the structural change. Maximum electromechanical factors kP=0.26 and k33=0.44, and remanent polarization Pr=11.8 µC/cm2 were obtained for the composition x=0.4.

Ferroelectricity and Phase Transformations in Pb(Mg1/3Nb2/3)O3-PbZrO3 Solid Solution Ceramics.

To elucidate the ferroelectricity and phase relations of the binary system of Pb(Mg1/3Nb2/3)O3–PbZrO3, solid solution ceramics having various compositions were synthesized by the conventional firing process, and their electrical and piezoelectric properties were measured as functions of composition and temperature. X-ray studies were also conducted to determine the crystal structure. As a result, the existence of the phase boundary between the normal ferroelectric and the relaxor ferroelectric states was observed, where the remanent polarization and electromechanical coupling factors showed considerable changes. Naturally, between these two ferroelectric states, marked differences in the dielectric behavior such as the temperature dependence and the dispersion were observed. In addition, lattice constants showed a slight anomaly in this boundary region.

Damping properties of metal-piezoelectric composites

Abstract For the purpose of searching for a new damping mechanism, the possibility of utilizing piezoelectric effects was investigated. Experiments of internal friction and electrical property measurements were made on some piezoelectric ceramics and metal–piezoelectric composites. Trials of manufacturing metal–piezoelectric composites are described. The method adopted is the pressing of a mixture of metal and piezoelectric powders into a metal tube, followed by rolling and annealing. Cu–PbTiO 3 composite showed three to five times higher damping compared to the pure Cu rod.

Dielectric and Piezoelectric Properties of the Solid Solution System Pb(Fe2/3W1/3)O3?PbZrO3

Solid solution ceramics having various ratios between Pb(Fe 2/3 W 1/3 )O 3 and PbZrO 3 were synthesized by a conventional solid state reaction. For well sintered specimens, dielectric, piezoelectric and ferroelectric properties were studied as a function of composition as well as of temperature. Maximum values obtained at room temperature are: the remanent polarization P r = 24.6 μC/cm 2 , the electromechanical coupling coefficient k 33 =0.32 and the piezoelectric constant d 33 =56.0x10 -12 C/N. Based on these experimental results combined with an XRD study, the phase diagram for the system of Pb(Fe 2/3 W 1/3 )O 3 -PbZrO 3 was finally determined, except for the narrow range near the end member Pb(Fe 2/3 W 1/3 )O 3 .

Electromechanical Properties of Hot-Pressed Pb(Fe1/2Ta1/2)O3 Ferroelectric Ceramics

Investigations were conducted on the ferroelectric properties of Pb(Fe1/2Ta1/2)O3 ceramics, in particular, on the electromechanical properties. Dense ceramic specimens prepared by the hot-pressing technique were used in this study. At the temperature of 158 K, the following values were obtained: e T33/e0=1450, P r=10.8 µ C/cm2, k33=0.390 and d33=131×10-12 C/N. These values were briefly compared with those of Pb(Fe1/2Nb1/2)O3 ceramics.

Ferroelectric and Antiferroelectric Properties of Solid-Solution Ceramics Ba(Ca1/3Nb2/3)O3-PbZrO3

Studies have been conducted regarding the solid solution of the binary system Ba(Ca1/3Nb2/3)O3-PbZrO3, as part of a series of investigations on the ternary system of the transparent ferroelectric ceramics Ba(Ca1/3Nb2/3)O3-PbZrO3-PbTiO3. First, the crystal structure of the complex compound Ba(Ca1/3Nb2/3)O3 at room temperature was determined; it has a cubic disordered perovskite structure with the lattice constant a=4.185 A. Then, for the system of xBa(Ca1/3Nb2/3)O3(1-x)PbZrO3, lattice constants, dielectric constants, electromechanical coupling factors, spontaneous polarization and thermal expansion were measured as a function of temperature for varying x (x=0-0.1). From these results, successive phase transitions from the paraelectric through the ferroelectric to the antiferroelectric phase were found. Finally, the diffuse phase transition for the composition x>0.05 was discussed.

Search for a Material with Temperature-Independent Piezoelectric Constant d31 in Nb-Modified Pb(Zr, Ti)O3 Ceramics

Investigations were made regarding the temperature characteristics of the piezoelectric constant d31 of Pb(Zr, Ti)O3 ceramics. The composition, Pb1-x/2(Zr0.52Ti0.48)1-xNbxO3, was exclusively used, and the amount of Nb, x, was controlled in detail. The specimen near x=0.012 was found to have a temperature-independent value of d31 over the temperature range between 20°C and 180°C.