Key Engineering Materials Vol. 566

Abstract: The piezoelectric response of [11-oriented, fine-grained BaTiO₃ ceramics was investigated. It was found that an exposure of the BaTiO₃ compacts to high-pressure, high-temperature steam in an autoclave promoted the orientation of the sintered ceramics. As temperature in the autoclave increased, the orientation increased. A large small-field piezoelectric constant of d₃₃ = 517 pC/N was observed for the oriented BaTiO₃ ceramics with the grain size of 1.76 μm and the Lotgering factor of 85.3 %.

Abstract: Grain-oriented 0.8(Bi_1/2K_1/2)TiO₃-0.2BaTiO₃ (BKT-BT20) ceramics were prepared by the Reactive Templated Grain Growth (RTGG) method. The BKT-BT20 ceramics sintered at 1070°C for 100 h. The grain-oriented BKT-BT20 exhibited relatively high orientation factor, F, of 0.87 and density ratio of 92%. A resistivity of textured BKT-BT20 was 1.29×10¹³ Ωcm. Piezoelectric strain constant, d₃₃, and the normalized strain, d₃₃^*, of the textured BKTBT20 ceramic in the direction parallel (//) to the tape stacking direction were 117 pC/N and 243 pm/V (at 80 kV/cm), respectively.

Abstract: Barium titanate (BaTiO₃, BT) nanoparticle accumulations were prepared by an electrophoresis deposition (EPD) method, and their dielectric properties were measured. The BTKK accumulation exhibited high dielectric constant of 100. To prepare the BT ceramic/polymer film capacitors, the polymer was injected into the accumulations in vacuum. Finally, dielectric properties were measured, and it was clarified that the dielectric constant of the ceramic/polymer film capacitors became smaller than those of the accumulation because of surfactant used as particle dispersion.

Abstract: Barium titanate (BaTiO₃, BT)-bismuth magnesium titanate (Bi (Mg_1/2Ti_1/2)O₃, BMT)-bismuth ferrite (BiFeO₃, BF) solid solution ceramics were prepared using a conventional solidstate synthesis, and their piezoelectric properties and microstructure were investigated. Strain electric field curves of the 0.3BT-0.1BMT-0.6BF ceramics with a single perovskite phase were ferroelectric butterfly-like curves. A strain maximum / electric field maximum (S_max/E_max) was 330 pm/V. Transmission electron microscopy revealed ferroelectric-like domain structure in the 0.3BT-0.1BMT-0.6BF ceramics.

Abstract: Single crystals of (K_,Na)Nb_1-xTa_xO₃ (KNNT) were grown by the top-seeded solution growth (TSSG) method under high oxygen pressure atmosphere (Po₂ = 0.9 MPa), and their dielectric properties were investigated along [10_cubic (the cubic notation). KNNT single crystals in a composition range of 0 x 0.65 were successfully obtained. Through the measurements of x-ray diffraction and dielectric properties, we propose a temperature (T)-composition (x) phase diagram in the KNNT system in which a successive phase transition from orthorhombic (Amm2), tetragonal (P4mm) to cubic (Pmm) occurs with increases in T and x.

Abstract: Li,Na,K)NbO₃ (LNKN) crystals were grown by an infrared convergence-type floating zone (FZ) method using SrTiO₃ seed crystals to control the crystallographic orientation. The crystals were grown along the [10 direction of SrTiO₃ seed crystal. It was a critical condition for the crystal growth that the descending speed of an upper shaft in the FZ furnace was faster than that of the lower shaft. The grown crystal sizes were about 10 mm in length and 5 mm in diameter. A relation between the Li content and T_c was investigated, and the result was compared with the case of polycrystalline ceramic samples.

Abstract: Recently, high performance lead-free piezoelectric materials are strongly demanded for environmental issues. (K0.5Na0.5)NbO3 (KNN) has been attracting interest as lead-free piezoelectric ceramics because of its high Curie temperature and excellent piezoelectric properties. In this study, we investigated effects of Li addition on piezoelectric properties of (Li,Na,K)(Nb+Ta)O3+CuO,BaTiO3 . We found that optimum Li ratio of A site and B site on the perovskite structure increases relative density and .

Abstract: Barium titanate (BaTiO₃, BT) - potassium niobate (KNbO₃, KN) nanostructured ceramics with artificial morphotropic phase boundary (MPB) structure were successfully prepared at temperatures below 230 °C by solvothermal method. Various characterizations suggested that the BT-KN nanostructured ceramics exhibited a porosity of around 30 % and heteroepitaxial interface between BT and KN. Their dielectric and piezoelectric properties were measured at room temperature, and the dielectric constant and apparent piezoelectric constant estimated from slope of strain and electric field curve was 370 and 136 pm/V, respectively.

Abstract: Aluminum substituted La₃Ta_0.5Ga_5.5O₁₄ (LTGA) single crystals were grown via a floating zone (FZ) method in N₂ or O₂ gas flows. Also, LTGA single crystals that were grown using the Czochralski method were annealed in N₂ or O₂ gas flows. The resistivity of these crystals was measured in a temperature range from 300 to 700°C. The LTGA crystals that were grown/annealed in the N₂ atmosphere showed higher resistivity by 1 order of magnitude as compared to those crystals grown/annealed in the O₂ atmosphere. Based on these results, we suggest that the difference in resistivity is due to the concentration of oxygen vacancy and interstitial oxygen ions.

Abstract: The structural, and dielectric and piezoelectric properties of 0.3BaTiO₃ - 0.1x (x= Bi (Mg_1/2Ti_1/2)O₃, Bi (Cu_1/2Ti_1/2)O₃, Bi (Cu_2/3Nb_1/3)O₃, (Bi_1/2K_1/2)(Cu_1/3Nb_2/3)O₃) 0.6BiFeO₃ ceramics were studied. The relative density of all the samples was more than 94 %. A single perovskite phase was obtained for the samples, and the crystal structure was pseudo-cubic. The Curie temperature of x=Bi (Mg_1/2Ti_1/2)O₃ and Bi (Cu_1/2Ti_1/2)O₃ system ceramics was higher than 400 °C. The apparent piezoelectric constant d₃₃* of x=Bi (Mg_1/2Ti_1/2)O₃, Bi (Cu_1/2Ti_1/2)O₃, Bi (Cu_2/3Nb_1/3)O₃ and (Bi_1/2K_1/2)(Cu_1/3Nb_2/3)O₃ system ceramics was 311, 212, 75 and 70 pm/V, respectively.