Yasuharu Hosono

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.

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.

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.

Crystal Growth of Pb[(Zn1/3Nb2/3)0.91Ti0.09]O3 Using a Crucible by the Supported Bridgman Method

Piezoelectric Pb[(Zn1/3Nb2/3)0.91Ti0.09]O3 (PZNT 91/9) single crystals with diameters of 40 mm were successfully grown from solution by the Bridgman method with a PbO flux supported on the bottom of the crucible. This type of Bridgman method is more suitable for growing large and heavy crystals than the hanging-type Bridgman method. Using a modified supporting method, a PZNT 91/9 single crystal was grown. The crystals were grown in a platinum crucible heated to 1,130°C, and the growth rate was 0.20–0.50 mm/h. The obtained crystals were about 40 mm in diameter×20 mm in length (200 g) and were light brown in color. The Curie temperature, Tc, ranged from 170 to 175°C. These results confirm that the Bridgman method using a supported crucible is useful for the mass production of large crystals of PZNT 91/9.

Crystal Growth and Some Properties of Lead Indium Niobate-Lead Titanate Single Crystals Produced by Solution Bridgman Method

A single crystal about 15 mm in diameter and 10 mm in length of the lead indium niobate-lead titanate, (1-x)Pb(In1/2Nb1/2)O3–xPbTiO3[PIN–PT(1-x/x)] solid solution system near a morphotropic phase boundary was obtained by the solution Bridgman method using PbO–B2O3 flux. X-ray diffraction study reveals that the ingot cut perpendicularly to the cylindrical as-grown PIN–PT(63/37)(the starting composition) single crystal length exhibits the (110) plane of the perovskite phase, and the wafers cut 2 mm and 10 mm from the bottom of the cylindrical PIN–PT single crystal exhibit the rhombohedral phase and tetragonal one at room temperature, respectively. The crystal growth was almost along the [110] direction. The Ti contents x of these wafers cut at 2 mm and at 10 mm were determined by Inductive Charge Plasma (ICP) chemical analysis to be 0.31 and 0.35, respectively. The Ti content of the as-grown PIN–PT(63/37)(the starting composition) single crystal was found to increase with growth away from the nucleation point. For x=0.31, the relative permittivity er has a peak (37000 at 10 kHz) at the Curie temperature Tc, 300°C and then a shoulder at the ferroelectric rhombohedral to tetragonal phase transition temperature, 120°C with cooling. For x=0.35, the er has a peak (25000 at 10 kHz) at Tc, 313°C.

Growth, Electric and Thermal Properties of Lead Scandium Niobate-Lead Magnesium Niobate-Lead Titanate Ternary Single Crystals

Single crystals of the xPb(Sc1/2Nb1/2)O3–yPb(Mg1/3Nb2/3)O3–zPbTiO3 (PSMNT 100x/100y/100z) ternary system have successfully been grown by a flux method using 71.4 mol% PbO–28.6 mol% B2O3 flux. The crystals were grown in a platinum crucible by mass crystallization achieved by the slow cooling of a 50PbO:20B2O3:30PSMNT 29/34/37 (mol%) molten solution from 1,200°C to 880°C at 1.2°C/h. The resulting two types of crystals, 2–3 mm in length with perovskite structure and 5–7 mm in length with pyrochlore structure, coexist. Inductive charge plasma (ICP) chemical analysis revealed that the composition of the pulverized powder of perovskite crystal is PSMNT 43/17/40, which is slightly different from the charged composition of PSMNT 29/34/37. One of the single crystals near the morphotropic phase boundary (MPB) showed a dielectric constant peak of 200°C. The grown PSMNT crystals show good thermal stability of the perovskite phase with partical decomposition starting at 1128°C and peritectic melting at 1308°C.

Large Piezoelectric Constant of High-Curie-Temperature Pb(In1/2Nb1/2)O3–Pb(Mg1/3Nb2/3)–PbTiO3 Ternary Single Crystal near Morphotropic Phase Boundary

Single crystals, with high Curie temperature (Tc), of the xPb(In1/2Nb1/2)O3–yPb(Mg1/3Nb2/3)–zPbTiO3 (PIMNT100x/100y/100z) ternary system near a morphotropic phase boundary were successfully grown by a conventional flux method using PbO–B2O3 flux. The crystals were grown in a platinum crucible by mass crystallization achieved through slow cooling of a 50PIMNT 16/51/33: 40PbO: 10B2O3 (mol%) molten solution from 1,230 to 850°C at 1.2°C/h. The obtained crystals had a perovskite structure. The largest crystal had dimensions of about 20×10×5 mm3. The dielectric constant after poling, e33T/e0, was 3,100 and the dissipation factor was 0.8% at room temperature. The temperature dependence of the dielectric constant showed a maximum at the tetragonal-to-cubic phase-transition temperature, Tc=187°C. The piezoelectric constant of d33=2,200 pC/N is the highest value so far reported for any piezoelectric material with Tc>185°C.

Effects of Fine Metal Oxide Particle Dopant on the Acoustic Properties of Silicone Rubber Lens for Medical Array Probe

The effects of fine metal oxide particles, particularly those of high-density elements (7.7 to 9.7 times 10³ kg/m³), on the acoustic properties of silicone rubber have been investigated in order to develop an acoustic lens with a low acoustic attenuation. Silicone rubber doped with Yb₂O₃ powder having nanoparticle size of 16 nm showed a lower acoustic attenuation than silicone rubber doped with powders of CeO₂, Bi₂O₃, Lu₂O₃ and HfO₂. The silicone rubber doped with Yb₂O₃ powder showed a sound speed of 0.88 km/s, an acoustic impedance of 1.35 times 10⁶ kg/m²s, an acoustic attenuation of 0.93 dB/mmMHz, and a Shore A hardness of 55 at 37degC. Although typical silicone rubber doped with SiO₂ (2.6 times 10³ kg/m³) shows a sound speed of about 1.00 km/s, heavy metal oxide particles decreased the sound velocities to lower than 0.93 km/s. Therefore, an acoustic lens of silicone rubber doped with Yb₂O₃ powder provides increased sensitivity because it realizes a thinner acoustic lens than is conventionally used due to its low sound speed. Moreover, it has an advantage in that a focus point is not changed when the acoustic lens is pressed to a human body due to its reasonable hardness.

Top-Seeded Solution Growth of Pb[(In1/2Nb1/2),(Mg1/3Nb2/3),Ti]O3 Single Crystals

The crystal growth of relaxor-based ferroelectric single crystals Pb[(In1/2Nb1/2),(Mg1/3Nb2/3),Ti]O3 (PIMNT) was investigated using the top-seeded solution growth (TSSG) method. The concentration of Pb(In1/2Nb1/2)O3 in a melt was chosen to be 0.24 mole, and that of Pb(Mg1/3Nb2/3)O3 was changed from 0.36 to 0.42 mole. A mixture of PbO+B2O3 was used as a flax and the melt composition was PIMNT/PbO/B2O3=70/29/1 wt%. The obtained crystals showed that the concentration of Pb(In1/2Nb1/2)O3 slightly changed but that of Pb(Mg1/3Nb2/3)O3 increased by about 12%, 0.05 mole, compared to those of the melt. All crystals had a complete perovskite structure. A crystal with a composition of Pb[(In1/2Nb1/2)0.24(Mg1/3Nb2/3)0.43Ti0.33]O3 was obtained, and its Curie temperature was Tc = 208°C and rhombohedral-to-tetragonal phase transition temperature was Trt = 120°C. A phase diagram for crystal growth near the morphotropic phase boundary mentioned above was obtained.

Temperature Dependence of Dielectric and Piezoelectric Properties of Pb(Zn1/3Nb2/3)O3–PbTiO3 Piezoelectric Single Crystals

Temperature dependence of the dielectric and piezoelectric properties of xPb(Zn1/3Nb2/3)O3–yPbTiO3 (PZNT 100x/100y) piezoelectric single crystals (PSC) was investigated to estimate the heat stability of their properties. The coupling factor rectangular bar mode k33′=81% of PZNT 91/9 decreased sharply at about 70°C and then decreased gradually toward the Curie temperature, Tc. On the other hand, the k33′=62% of PZNT 95.5/4.5 hardly changed up to 110°C, although it was lower than that of PZNT 91/9 at room temperature. The degradation temperatures of the k33′ value were roughly in agreement with the phase-transition temperature, Trt, from rhombohedral to tetragonal, measured using the poled PZNT PSC. A large dielectric hysteresis was observed when PZNT PSC was heated to a temperature higher than the Trt, measured using poled PZNT PSC. Although PZNT 95.5/4.5 with reduced Ti content had a higher Trt, the obtained piezoelectric properties were inferior to those of PZNT 91/9 near the morphotropic phase boundary (MPB). Therefore, it is necessary to design the PSC composition carefully, considering specific applications in order to achieve the optimum balance between piezoelectric property and its heat stability.