Yoshikazu Akiyama

Actuation Properties of Lead Zirconate Titanate Thick Films Structured on Si Membrane by the Aerosol Deposition Method.

The results of the direct deposition of lead zirconate titanate [Pb(Zr0.52, Ti0.48)O3] (PZT) thick film on a Si-based structure are presented. The construction of a bottom electrode is very important for successful deposition. The actuation properties of PZT on the Si membrane were investigated. For a 6.2×6.1 mm2, 65-µm-thick Si membrane driven by a 4.7×4.3 mm2, 13-µm-thick PZT layer, the deflections, which were 1.5 µm upon applying 52 V at nonresonance frequency and 22 µm upon applying 8 V at resonance frequency, were measured.

Low-Temperature Sintering and Properties of (Pb, Ba, Sr)(Zr, Ti, Sb)O3 Piezoelectric Ceramics Using Sintering Aids

Low-temperature sintering of (Pb0.86Ba0.04Sr0.12)(Zr0.56Ti0.44Sb0.02)O3 (PBSZT) powders was investigated using Pb5Ge3O11 (PGO) or LiBiO2 (LBiO) as sintering aids. 1 wt% PGO or 1 wt% LBiO-added PBSZT powders could be densified into sintered bodies at 800°C for 2 h with a relative density of approximately 96%. The addition of PGO or LBiO significantly improved the sinterability of PBSZT powders, resulting in a reduction of sintering temperature by about 200°C. Dielectric and piezoelectric properties of LBiO-added PBSZT ceramics were superior to those fabricated without sintering aids. However, the addition of PGO was not effective in improving the dielectric and piezoelectric properties. This may be attributable to the microstructural change involving the solid solution reaction between the PBSZT matrix and the PGO additive. The 1 wt% LBiO-added PBSZT bodies sintered at 1000°C exhibited a dielectric constant of 2600, remanent polarization of 14.7 µC/cm2, and longitudinal strain of 0.24%

Low-Temperature Sintering of LiBiO2-Coated Pb(Mg1/3Nb2/3)O3-PbZrO3-PbTiO3 Powders Prepared by Surface Chemical Modification Method and Their Piezoelectric Properties

Low-temperature sintering of LiBiO2-coated 0.375Pb(Mg1/3Nb2/3)O3-0.25PbZrO3-0.375PbTiO3 (PMN-PZT) powders was investigated with surface modification through the hydrolysis of lithium ethoxide and bismuth tri-t-amiloxide on the surface of PMN-PZT powders, and their microstructure and piezoelectric properties were examined. By using the surface chemical modification method, PMN-PZT powders were homogeneously coated with LiBiO2 precursor fine particles of 20–30 nm. PMN-PZT bodies sintered at temperatures from 800 to 1000°C with a chemically added LiBiO2 sintering aid exhibited more homogeneous microstructures and improved piezoelectric properties than the specimens fabricated with LiBiO2 added by a conventional mixing method. 0.75 wt% LiBiO2-added PMN-PZT ceramics fabricated at 950°C for 4 h showed a high density of approximately 7.7 g/cm3, and their electromechanical coupling factor (kp) and piezoelectric coefficient (d33) were 61.8% and ~517 pm/V, respectively. And also, a large field-induced strain of ~0.17% and a well-saturated hysteresis loop with a remanent polarization (Pr) of 33.9 µC/cm2 were observed under an applied electric field of ±40 kV/cm.

Development of Lead Zirconate Titanate Family Thick Films on Various Substrates

We propose a POS (Piezo on Silicon) actuator, which comprise piezoelectric materials on a silicon substrate, and the actuation mechanism uses a bending vibration of a unimorph structure. Realization of this device was attempted, and the low-temperature sintering of piezoelectric ceramics, optimization of the screen-printing method and the barrier layer on a silicon substrate were developed. Regarding PMN–PZ–PT and PNN–PZ–PT bulk samples, a sintering temperature of 850°C became possible with the addition of Li–Bi oxide. Pt–Rh/TaN was used as a barrier layer, and a 30 µm-thick PNN–PZ–PT film prepared at 900°C on a Si substrate with a Pt–Rh/TaN buffer layer exhibited er = 2290, Ec = 8.6 kV/cm and Pr = 5.7 µC/cm2.

Development of (Pb, Nb)(Zr, Sn, Ti)O3 Film Using a Sol-Gel Process and Resulting Antiferroelectric Properties

(Pb, Nb)(Zr, Sn, Ti)O3 films are developed on Pt-coated Si substrates using a sol-gel process and their electronic properties are studied. An excessive amount of Pb in precursor solution is necessary to obtain films with good crystallinity. A 2.4-µm-thick film annealed at 650°C shows a dielectric constant of about 400 at room temperature. Electric field intensity at the antiferroelectric-to-ferroelectric phase transition is 80 kV/cm. Spontaneous polarization is 28 µC/cm2. Spontaneous polarization in this film is close to that observed in bulk samples (sintered at 1270°C). The electric field intensity, however, is approximately twice that of bulk samples.

Piezoelectric and Dielectric Properties of (Bi,Na,K,Ag)TiO3–BaTiO3 Lead-Free Piezoelectric Ceramics

Lead-free (1-y)(Bi0.5Na0.49-xKxAg0.01)TiO3–yBaTiO3 (x=0 to 0.1, y=0 to 0.04) [abbreviated as BNKAT-BT-100x/100y] piezoelectric ceramics were fabricated using various amounts of K and Ba substitutions, and their piezoelectric and dielectric properties were investigated. The crystal structure significantly changed with the amount of K substitution. The BNKAT-BT-5/2 specimens exhibited a pseudocubic structure, while the BNKAT-BT-10/2 specimens exhibited a tetragonal structure and provided a larger electrostrain constant (d33*) than BNKAT-BT-0/2 specimens, which exhibited a rhombohedral structure. The addition of La2O3/MnO to BNKAT-BT specimens affected the crystal structure and electrical properties. La2O3/MnO-added BNKAT-BT-10/100y (0.02y0.03) specimens with a pseudocubic structure exhibited P–E hysteresis loops different from those that are characteristic of ferroelectric, and provided a peculiar field-induced strain without the residual strain in the butterfly curve and a very large strain constant (d33*) of 415 pm/V. This may be associated with the field-forced phase transition from the paraelectric phase to the ferroelectric phase.

Enhancement of Piezoelectric Properties of Low-Temperature-Fabricated Pb(Mg1/3Nb2/3)O3-PbZrO3-PbTiO3 Ceramics with LiBiO2 Sintering Aid by Post-Annealing Process

The improvement of the piezoelectric properties of low-temperature-fabricated 0.375Pb(Mg1/3Nb2/3)O3-0.25PbZrO3-0.375PbTiO3 (PMNZT) ceramics with a LiBiO2 sintering aid was investigated by adopting a post-annealing process. The sinterability of PMNZT powders was markedly enhanced by liquid phase sintering with the addition of LiBiO2, resulting in a decrease in the required sintering temperature from 1000 to 800°C and the formation of a grain boundary layer. And, it was confirmed by a transmission electron microscope-X-ray energy-dispersive spectrometry (TEM-EDS) that the secondary phase along grain boundaries, which deteriorated the piezoelectric properties, included Pb diffused from PMNZT grains as well as Bi from the LiBiO2 additive. The secondary phase along grain boundaries was significantly removed by annealing after sintering. The 0.75 wt% LiBiO2-added PMNZT ceramics sintered at 800°C for 2 h with post-annealing at 800°C for 10 h exhibited a higher electromechanical coupling factor (kp) of 60.8% and a higher piezoelectric coefficient (d33) of 504 pm/V (at 15 kV/cm), compared with those of the sintered specimens without post-annealing. Also, LiBiO2-added PMNZT multilayer ceramics with Ag internal electrodes were successfully sintered at 800°C. The post-annealed multilayer ceramics sintered at 800°C exhibited a higher d33 value of 506 pm/V. Thus, a low-temperature sintering technique with post-annealing for the removal of the grain boundary layer without deteriorating piezoelectric properties was established.

Fabrication and Characterization of (100),(001)-Oriented Reduction-Resistant Lead-Free Piezoelectric (Ba,Ca)TiO3 Ceramics Using Platelike Seed Crystals

The preparation of reduction-resistant (Ba,Ca)TiO3 ceramics as lead-free piezoelectric materials was studied. To improve their electrical properties, (100),(001)-oriented (Ba0.85Ca0.15)TiO3 ceramics were fabricated by the reactive templated grain growth method using a mixture of platelike CaTiO3 and BaTiO3 particles. The platelike CaTiO3 and BaTiO3 particles were prepared through a topochemical microcrystal conversion process using CaBi4Ti4O15 and BaBi4Ti4O15 plate-like precursor crystals. The 100 orientation degree of the grain-oriented (Ba0.85Ca0.15)TiO3 ceramics was 92%, as estimated by Lotgerings equation. In addition, 1 mol % Ba excess and 1 mol % Mn-doped (Ba0.85Ca0.15)TiO3 sintered bodies, which were sintered at 1350 °C in an Ar flow containing H2 (0.3%), had sufficient resistivity to allow the characterization of electrical properties. The ferroelectric and field-induced strain properties of the (Ba0.85Ca0.15)TiO3 ceramics, sintered in the reducing atmosphere, were markedly improved as a result of fabricating grain-oriented samples. The field-induced strain coefficient (estimated from the slope of the unipolar strain loop) of the nonreducible (100),(001)-oriented (Ba0.85Ca0.15)TiO3 ceramics reached 570 pm/V, which was higher than that of polycrystals (260 pm/V) with no preferential orientation.

Purification of Head-to-Tail-Type Regioregular Poly(3-hexylthiophene), HT-P3HexTh, and Investigation of the Effects of Polymer Purity on the Performance of Organic Field-Effect Transistors

Analytically pure head-to-tail-type poly(3-hexylthiophene-2,5-diyl), HT-P3HexTh, has been obtained by the slow reprecipitation of the polymer. A FET made of purified HT-P3HexTh yielded a typical FET I–V curve with saturation and showed a five fold higher FET mobility than that of conventionally used HT-P3HexTh.

Field-Induced Antiferroelectric-to-Ferroelectric Phase Transition of Lead Niobium Zirconate Titanate Stannate Ceramics

The elastic strain behavior associated with the field-induced antiferroelectric-to-ferroelectric phase transition has been investigated for Pb0.99Nb0.02[(Zr1-x Snx )1-y Tiy ]0.98O3 ceramics (PNZST) by means of dielectric, polarization and strain hysteresis measurements. As the applied electric field intensity increased, a sudden increase in the strain was observed along with a corresponding change in polarization that is attributable to the phase transition. PNZST ceramics with optimized composition exhibit a huge strain value of 0.44%, which may make the development of a new functional transducer device possible.