Key Engineering Materials Vol. 485

Abstract: ANbO₃ – BaTiO₃ (A=K, Na, or K_0.5Na_0.5) system ceramics were prepared using a conventional sintering method, and their dielectric properties were investigated. It was found that the dielectric constant of KNbO₃-BaTiO₃ and (K_0.5Na_0.5) NbO₃- BaTiO₃ system ceramics did not strongly depend on temperature between 20 and 400 °C, making them useful for capacitor application.

Abstract: Re-oxidation is an important thermal process to minimize oxygen vacancies and produce high reliable Ni-MLCCs. The re-oxidation of these devices is then investigated with a series of “in-situ” impedance measurements between 400 and 500 °C in air. From the relative impedance change, chemical diffusion coefficients, associated activation energy and effective equivalent circuit model are determined. Those values were found to be reasonable compared with previous researchers’ data. Moreover, the proposed effective equivalent circuit model successfully represents the real Ni-MLCC morphology. From transmission electron microscopy (TEM) and electron energy loss spectroscopy (EELS), it is found that the electrical properties and reliabilities of the Ni-MLCCs re-oxidized under different conditions are identical.

Abstract: Electric potential mapping of degraded dielectric layers of multilayer ceramic capacitors (MLCCs) was carried out using Kelvin probe force microscopy in order to clarify their degradation mechanism under conditions of an accelerated lifetime test condition. In the cross sections of the degraded and as-prepared dielectric layers, a significant electric field concentration was found in the vicinity of the anode of the degraded dielectric layer, in contrast to a homogeneous concentration found throughout layers of the samples before the accelerated lifetime test.

Abstract: Na_0.5K_0.5NbO₃ (NKN) lead-free piezoelectric ceramics was synthesized by a mixed oxide reaction method. The ceramics was poled under an electric field of 3 kV/mm at 150 °C for 0.5 h. The thermally stimulated depolarization current (TSDC) measurement was carried out at the heating rate of 1 °C/min from room temperature up to 500 °C under an applied voltage of 0 and 0.5 V. The zero-bias TSDC pattern showed broad patterns around at 365 and 375 °C. These temperatures corresponded to the temperatures showing bending points in the Arrhenius plot of TSDC measured under 0.5 V. The oxygen vacancy related electrical conduction was changed at 313 °C at the heating step. The mobile oxygen vacancy in NKN ceramics was piled up under the poling field, and the oxygen vacancy was diffused at temperature higher than 313 °C.

Abstract: The Relationship between the Piezoelectric Properties and Crystal Lattice Deformation and Distortion Resulting from the Li Substitution in Li_XNa_0.52K_0.48-XNbO₃, Alkaline Niobate-Based Perovskite Ceramics of (Li, Na, K)NbO₃, Was Investigated. the Lattice Parameters of the Sample with a Li Content X = 0.05 and Having a Monoclinic System with Space Group PM Were a = 3.9789(6) Å, B = 3.9385(5) Å, C = 4.0134(6) Å, and B = 90.305(4)º. the E^T33/e0, Kr, and -D31 Values of the Sample by Poling in the Monoclinic System Were 450, 44.6%, and 57 PC/N, Respectively. on the other Hand, the E^T33/e0, Kr, and -D31 Values of the Sample by Poling in the Tetragonal System Were 600, 38.7%, and 56 PC/N, Respectively. the Remarkable Piezoelectric Properties of these Ceramics Can Be Attributed only to the Low Symmetry of their Monoclinic System, which Is a Subgroup of aMm2 and P4mm. Li_0.05Na_0.52K_0.43NbO₃ Ceramics with a Monoclinic System Were Observed to Have the Unique Piezoelectric Characteristics.

Abstract: Porous potassium niobate (KNbO₃, KN) system ceramics were prepared by a conventional sintering method using carbon black (CB) nanoparticles. First, KN nanoparticles with a size of 100 nm was mixed with CB nanoparticles and binder using ball milling with ethanol. The mixture was dried, and pressed into pellets using uniaxial pressing. After binder burnout, these ceramics was sintered in air. Their piezoelectric properties were measured and discussed a relationship between porosity and piezoelectric properties. As the results, with increasing porosity, piezoelectric g₃₃ constant increased significantly, which suggested that porous ceramics were effective for stress sensor application.

Abstract: The ZnO based glass was added to calcined K_0.5Na_0.5NbO₃ by ball milling for 20h. The addition of 1wt.% ZnO- based glass exhibited the following piezoelectric properties (kp=36%, Qm=236, e₃₃^T/e₀=464). By increasing the amount of glass powder ~5wt.%, kp was decreased to 24%. However, Qm and e₃₃^T/e₀ were observed slightly decreasing. Besides, the moisture-resistance of ZnO-based glass added K_0.5Na_0.5NbO₃ was enhanced considerably as compared to that of K_0.5Na_0.5NbO₃.

Abstract: In this study, the relationships between the electrical properties and polarization switching of lead-free (Li_0.06Na_0.94)NbO₃ (LNN6) ceramics were investigated. The electrical properties of stoichiometric LNN6 did not change with polarization switching. On the other hand, the frequency dependence of the impedance of Na-deficient LNN decreased with polarization switching, and the coupling factor k_p, the piezoelecric constant d₃₃ and the dielectric constant ε33T/ε0 decreased with polarization switching. Moreover, the dielectric curve of Na-deficient LNN6 after 10 switchings showed peaks at approximately 330, 400 and 500 °C

Abstract: High-performance single crystals of ferroelectric Bi₄Ti₃O₁₂ (BiT) have been successfully obtained via the top-seeded solution growth under high oxygen pressure (Po₂) atmosphere. Crystals grown at 960°C at a Po₂ of 0.9 MPa exhibited a well-saturated hysteresis loop with a remanent polarization of 48 mC/cm² and a coercive field of 29 kV/cm. The results of piezoresponse force microscopy indicate that polarization switching is accomplished throughout the BiT crystals obtained. Electric-field-induced strain measurements along the a axis yield a piezoelectric constant d₁₁* of 37 pm/V for BiT.

Abstract: The Barium titanate (BaTiO₃, BT) [110] grain-oriented ceramics along [110] direction were prepared by a templated grain growth (TGG) method. The [110] oriented BT platelike particles (t-BT) were used as template particles. The relationship between poling treatment program and piezoelectric constant was investigated. The change in the poling conditions did not greatly influence domain size and the piezoelectric constant. The relationship between piezoelectric properties and domain size in BT grain-oriented ceramics was investigated. The smaller domain size was required to increase the piezoelectric constant.