Key Engineering Materials Vol. 320

Abstract: The microstructural development of crystalline-oriented (K0.5Na0.5)NbO3 (described as KNN hereafter)-based piezoelectric ceramics during sintering was investigated. The addition of CuO as a sintering aid was found to be effective for fabricating highly oriented and dense KNN ceramics. KNN specimens with 0.5-1.0 mol% CuO sintered at 1100°C for 1 h have both a relative density and a pseudo-cubic {100} orientation degree of 95% or higher. In the early stages of sintering, KNN is formed in the reaction between complementary reactants NaNbO3 and KNbO3, after which oriented grain growth proceeds at a relative density of more than 90%. In addition, the results of TEM observation showed that textured KNN ceramics have a unique pectinate-like domain structure, in which the domain walls consist of {101} planes.

Abstract: Nanoparticles and thin films of potassium niobate KNbO3 were prepared using a unique solution reaction at room temperature. Precursor solutions and as-prepared samples were characterized by Raman spectroscopy. The data demonstrated that the niobate nanosheets consist of distorted Nb-O polyhedra.

Abstract: [BaO]m(Ti0.975Zr0.025)O2 ceramics with Ni electrodes were prepared by a firing in N2 atmosphere. The dielectric, ferroelectric and piezoelectric properties were examined in terms of the composition. The remanent polarization of 9.5μC/cm2 was obtained for m=1.01 by the addition of 0.5wt% SiO2. The longitudinal piezoelectric constant d33 calculated from a unipolar signal (8kV/cm,10Hz) was 430pC/N. Lead-free multi-layered piezoelectric actuators were fabricated using this material by the tape casting, screen-printing of Ni electrodes, laminating under heat and pressure, and firing in N2 atmosphere. The displacement of the actuator with 75μm x 9 active piezoelectric layers was 0.17μm at an applied voltage of 75V and a frequency of 10Hz.

Abstract: A study has been done for the piezoelectric properties in texured ceramics of SrBi2Nb2O9 (SBN) fabricated by the templated grain growth (TGG) method. Remanent polarization along to the stacking direction increased with the orientation degrees. That corresponds to the increases in electro-mechanical coupling coefficient with orientation degree. The temperature coefficient of the resonant frequency (TCF) in thickness sheer vibration mode changed from negative to positive with increasing orientation degrees, and an excellent TCF of -0.4 ppm/°C was obtained for the specimen with an orientation degree of 76%.

Abstract: Measurements of the leakage-current and polarization properties in bismuth titanate (Bi4Ti3O12) along the a axis show that the crystals grown in air followed by air annealing at 700oC had a superior remanent polarization of 48 μC/cm2 as well as a low leakage current density of the order of 10-9 A/cm2. The annealing at a high oxygen partial pressure of 35MPa (700oC) resulted in a higher leakage current, indicating that electron holes arising from the incorporation of oxygen at oxygen vacancies act as detrimental carriers for electrical conduction at room temperature. A crystal growth under high-pressure oxygen atmosphere and subsequent annealing at a moderate oxygen partial pressure is proposed to be advantageous for suppressing the vacancy formation and for attaining a large remanent polarization as well as a high insulating property of the Bi4Ti3O12 system.

Abstract: The piezoelectric properties of a solid solution based on the three components of bismuth sodium titanate, (Bi1/2Na1/2)TiO3 (BNT), bismuth potassium titanate, (Bi1/2K1/2)TiO3 (BKT), and barium titanate, BaTiO3 (BT), that is, x(Bi1/2Na1/2)TiO3-y(Bi1/2K1/2)TiO3-zBaTiO3 [BNBKy:z(x); x+y+z=1] are investigated. Fine piezoelectric properties in lead-free piezoelectric ceramics were obtained near the MPB composition, and the highest electromechanical coupling factors, k33 and kp, and piezoelectric constant, d33, were 0.58 and 0.36 for BNBK2:1(0.89) and 181 pC/N for BNBK2:1(0.88), respectively. In this study, we also measured the depolarization temperature, Td, from the temperature dependence of dielectric and piezoelectric properties.

Abstract: Influence of annealing on the domain structures of bismuth titanate (BiT) and rare-earth (La and Nd)-substituted BiT crystals (BLT or BNT) were investigated by optical microscope and piezoresponse force microscope (PFM). Annealing of BiT at 950°C in air significantly decreased the number of striped 90° domain walls, while charged 180° domain walls were still present in the crystals after the annealing. The annealing for the crystals of BLT and BNT at the same condition did not change their 90° domain structures. PFM observations indicated that antiphase domain boundaries in BLT play an important role in the formation of 90° domain structures.

Abstract: Vanadium-substituted strontium bismuth niobate, SrBi2Nb2-xVxO9 (SBNVx), ceramics were synthesized by a low-temperature ceramic fabrication process; their electric properties were characterized, and grain orientation effects on their electric properties were also investigated using a hot-forging (HF) method. Resonance characteristics of the (33) and (15) modes of grain-oriented SBNV0.1 (HF) showed relatively high electromechanical coupling factors of k33=0.272 and k15=0.151 as well as piezoelectric constants of d33=31.7 pC/N and d15=24.8 pC/N. The temperature dependences of the resonance frequency (TC-f) of the (33) and (15) modes of the SBNV0.1(HF) ceramics were -16.5 ppm/°C and –25.5 ppm/°C, respectively.

Abstract: Large Bi0.5Na0.5TiO3 (BNT) single crystals with 10 mm × 10 mm × 5 mm were successfully grown by a flux method using BNT powder and the mixed flux composed of Bi2O3 and NaF. Dielectric measurements show a dielectric-permittivity peak at 310°C, which is the result of the gradual phase transition from rhombohedral (R3c) to tetragonal (P4bm) structure. Electric-field induced strain measurements along [100]C reveal that the effective piezoelectric strain constant (d33 *) was estimated to be 130 pm/V in a multidomain state.

Abstract: The piezoelectric properties of Nd and V cosubstituted bismuth titanate ceramics, (Bi4-y,Ndy)1-(x/12)(Ti3-x,Vx)O12 [BNTV-y (x=0.01, y=0.00~1.00)] , are investigated. Furthermore, the grain orientation effects of BNTV-y ceramics on their piezoelectric properties are studied by the hot forging (HF) method. The electromechanical coupling factor, k33, of ordinarily fired (OF) BNTV-y0.75 ceramic was 0.21, which is one of the highest k33 values for bismuth layer-structured ferroelectrics (BLSFs). On the other hand, the k33 of the grain oriented (HF) BNTV-y0.25 ceramic was 0.30.