Yohachi Yamashita

Large Electromechanical Coupling Factors in Perovskite Binary Material System

Similarities of large electromechanical coupling factors (k s) in perovskite binary material systems were studied. Five large-k s material systems, PZT 53/47, PZNT 91/9, PMNT 67/33, PSTT 55/45 and PSNT 57/43, were compared. These five large-ks material systems were found to show four similarities: rhombohedral and tetragonal morphotropic phase boundary (MPB), large polarization (P r>25 µ C/cm2), proper B1 ionic size (70–72 pm) and large B2 ion (64 pm) in Pb(B1, B2)O3 relaxors and proper B-site average ionic sizes of MPB composition (64.7–66.8 pm). For example, in this study, the maximum coupling factors (k p=72 %, k31=45 %, and k33=77 %) were obtained in Pb[(Sc1/2Nb1/2)0.57Ti0.43]O3+0.005Nb2O5(PSNTN 57/43) piezoelectric ceramic materials.

Crystal Growth and Electrical Properties of Lead-Free Piezoelectric Material (Na1/2Bi1/2)TiO3–BaTiO3

Single crystals of lead-free piezoelectric material x(Na1/2Bi1/2)TiO3?yBaTiO3 (NBBT 100x/100y) have been successfully grown by the flux method and the Bridgman method. Using the flux method, crystals having an edge length of 2?8 mm were obtained using Bi2O3 flux with cooling from 1350?C to 800?C at a rate of 3.5?C/h. Using the Bridgman method, comparatively good crystal of 15 mm diameter and 50 mm length was obtained using Bi2O3 flux with the Pt crucible driven down through the heat zone at a speed of 1.0 mm/h. The resulting crystals showed single-phase perovskite structure. Inductively charged plasma (ICP) chemical analysis revealed that the composition of the pulverized powder of these crystals is NBBT 97/3, which is slightly different from the charged composition of NBBT 94/6. One of the single crystals grown by the Bridgman method showed a dielectric constant of 1230 at room temperature and a dielectric constant peak at 313?C.

An Improved Phased Array Ultrasonic Probe Using 0.91Pb(Zn1/3Nb2/3)O3?0.09PbTiO3 Single Crystal

A 96-channel phased array probe for echocardiography using a single-plate, 0.91Pb(Zn1/3Nb2/3)O3–0.09PbTiO3 (PZNT 91/9) single-crystal transducer with dimensions of 14×20 mm has been fabricated to realize greater sensitivity and broader bandwidth properties. The center frequency of the probe, 3.5 MHz, was selected to cover the bandwidths of two conventional lead zirconate titanate (PZT) ceramic probes with center frequencies of 2.5 and 3.75 MHz. A solder paste was used to connect a flexible printed circuit to the PZNT 91/9 transducer. The echo amplitude of the PZNT 91/9 probe is about 6 dB higher than that of the two PZT probes, and the fractional bandwidths are 30 and 25 percentage points wider, respectively. The B-mode image quality of the PZNT 91/9 probe is comparable to that of the two PZT probes, and the Doppler sensitivity of the PZNT 91/9 probe is almost equal to that of the 2.5 MHz PZT probe, which means that the PZNT 91/9 probe matches both the penetration of the 2.5 MHz PZT probe and the resolution of 3.75 MHz PZT probe.

Dielectric and Piezoelectric Properties of Pb(In1/2Nb1/2)O3–Pb(Mg1/3Nb2/3)O3–PbTiO3 Ternary Ceramic Materials near the Morphotropic Phase Boundary

The physical and electrical properties of xPb(In1/2Nb1/2)O3(PIN)–yPb(Mg1/3Nb2/3)O3(PMN)–zPbTiO3(PT) (PIMNT 100x/100y/100z) ternary ceramic materials near the morphotropic phase boundary (MPB) were investigated. The MPB follows an almost linear region between the PIMNT 63/0/37 and PIMNT 0/68/32 MPB compositions of the binary systems. All the sintered ceramics show a complete perovskite structure. The maximum dielectric constants decrease as the function of PIN content increases. The maximum electromechanical coupling factor, kp=67.6%, is found at PIMNT 24/42/34, where dielectric constant, e33T/e0=2,120, piezoelectric constant, d33=505 pC/N, and Curie temperature, Tc=219°C, are obtained.

Piezoelectric properties of niobium-doped [Pb(Sc1/2Nb1/2)1-xTix]O3 ceramics material near the morphotropic phase boundary

The physical and electrical properties of Pb[(Sc1/2Nb1/2)1-x Tix ]O3 (x=0.40–0.45)+0.01 PbNb2 O6 piezoelectric polycrystalline ceramic materials near the morphotropic phase boundary (MPB) were investigated. The maximum dielectric constant (e33 T/e0=3200) and maximum piezoelectric constant (d33=590×10-12 m/V) were found at x=0.435, where the coupling factors were k p=67 %, k31=41 %, and k33=74 %. The maximum electromechanical coupling factors, (k p=71 %, k31=44 %, and k33=77 %) were found at x=0.420, where e33 T/e0=2080 and d33=480×10-12 m/V were obtained. The x=0.420 composition exhibited the largest electromechanical coupling factor of all binary piezoelectric ceramics systems so far reported, including the most widely used conventional ceramic, Pb(Zr1-x , Tix )O3.

A 3.7 MHz phased array probe using 0.91Pb(Zn/sub 1/3/Nb/sub 2/3/)O/sub 3/-0.09PbTiO/sub 3/

A novel 128-channel phased array probe for echocardiography with a center frequency of 3.7 MHz using 0.91Pb(Zn(1/3)Nb(2/3))O(3)-0.09PbTiO(3 ) (PZN-9%PT) single crystal has been fabricated to realize greater sensitivity and broader bandwidth properties. The echo amplitude of the PZN-9%PT single-crystal probe is about 5 dB higher than that of the conventional lead airconate titanate (PZT) ceramic probe, and the fractional bandwidth is about 25 percentage points broader. The quality of B mode images obtained by the PZN-9%PT probe satisfies the performance of the two types of conventional PZT ceramic probes that have center frequencies of 2.5 and 3.75 MHz. At the reference frequency of 3 MHz, the Doppler sensitivity of the PZN-9%PT probe is about 5 dB higher than that of the 3.75 MHz PZT probe; the blood flow of a pulmonary vein in a hard-to-image patient is much more clearly imaged than in the case of using the PZT probe. These superior images are attributable to the use of sufficiently large PZN-9%PT single crystals obtained by the self-flux method.

Improved ferroelectric properties of niobium-doped Pb[Sc1/2Nb1/2)Ti]O3 ceramic material

The effects of doping niobium and scandium in Pb[(Sc1/2Nb1/2)0.575Ti0.425]O3 piezoelectric polycrystalline ceramics were investigated. Complete single-phase perovskite with high density was obtained with all samples fired at 1275?C. Niobium doping decreased the grain size, enhanced the maximum dielectric constant value and increased the electrical resistivity by two orders of magnitude compared with nondoped samples. Large electromechanical coupling factors of kp=69%, kt=52% and k33=76%, which are almost equivalent to value for the best PZT-based piezoelectric ceramics, were obtained in niobium-doped specimens. The material has the largest electromechanical coupling factor of all relaxor-lead titanate binary ceramics systems so far reported.

Optical Observation of Heterophase and Domain Structures in Relaxor Ferroelectrics Pb(Zn1/3Nb2/3)O3/9%PbTiO3

Phase boundary and domain structure in relaxor ferroelectrics Pb(Zn1/3Nb2/3)O3/9%PbTiO3 were observed using a (111) plate under a polarization microscope. The dielectric constant was measured simultaneously to determine exact transition temperatures and to connect the dielectric behavior with phase boundary movements. Movement of the phase boundary between cubic and tetragonal phases was observed at the temperature Tc where the dielectric constant changed abruptly. Below Tc, tetragonal and rhombohedral phases coexisted over a wide temperature range. The complicated domain/phase patterns are classified into two blocks according to extinction position. The difference in extinction positions between the two blocks deviated from 30? and manifested temperature dependence. This fact indicates that the symmetry-lowering occurs in the heterophase. A small, but the distinct temperature hysteresis of the dielectric constant was related to the nucleation and growth of one phase into another phase.

Synthesis of lead scandium niobate-lead titanate pseudo binary system single crystals

Single crystals of the Pb[(Sc{sub 1/2}Nb{sub 1/2}){sub 1{minus}x}Ti{sub x}]O{sub 3} (PSNT) pseudo binary system have been successfully obtained by a flux method using PbO-B{sub 2}OI{sub 3} flux. The crystals were grown in a platinum crucible by mass crystallization, achieved by slow cooling the solution at 3C/h from 1,200 to 800 C. The resulting crystals are 2 to 7 mm in length. Chemical analysis and X-ray studies revealed that the crystals are of the Perovskite structure with x = 0.33 to 0.37, making them slightly different from the charged polycrystalline composition of a morphotropic phase boundary, where x = 0.42.

Crystal Growth and Dielectric Properties of Solid Solutions of Pb(Yb1/2Nb1/2)O3?PbTiO3 with a High Curie Temperature near a Morphotropic Phase Boundary

The Pb(Yb1/2Nb1/2)O3–PbTiO3 (PYN–PT) binary system single crystal near the morphotropic phase boundary (MPB) composition with (100) planes of 1–2 mm length on one side was successfully grown by the flux method using PbO–PbF2–B2O3 flux. The PYN–PT (47/53) single crystal was found, by simultaneous microdifferential thermal analysis and thermogravimetric analysis, to show a peritectic melting point at 1205°C with a decomposition of the perovskite crystals into a pyrochlore phase and a liquidus point at 1253°C. The structure of the PYN–PT (47/53) single crystal was determined by X-ray diffraction study to be tetragonal with a=4.05±0.01 A and c=4.14±0.01 A at room temperature. The PYN–PT single crystal shows the maximum value of the relative permittivity er of 16000 at 1 kHz at a Curie temperature Tc of 404°C, which is as high as that in the Pb(Zr, Ti)O3 system near the MPB and the value of the remanent polarization Pr of about 26 µC/cm2 at 140°C.