Key Engineering Materials Vol. 566

Abstract: The effects of adding Sb to a BiMnCoSiCrNiYZr-added ZnO varistor (with the same composition as a commercial varistor) on the varistor voltage, leakage current, and resistance to electrical degradation were investigated. Bi is incorporated in spinel particles, and δ-Bi₂O₃ eventually disappears with the addition of small amounts of Bi, especially as the amount of Sb₂O₃ added increased. Reduction in both the nonlinearity index and the amount of δ-Bi₂O₃ for small amounts of added Bi with the addition of more than approximately 1.25 mol% Sb₂O₃ demonstrates that Sb inhibits Bi₂O₃ from forming deep interfacial impurity levels at the grain boundaries. The sample containing 1.2 mol% Bi₂O₃, 1.0 mol% ZrO₂, 1.0 mol% Y₂O₃, and 1.5 mol% Sb₂O₃ added exhibits a high varistor voltage (approximately 630 V/mm), high resistance to electrical degradation and low leakage current.

Abstract: Synthesis of U-type hexaferrite was investigated in the various strontium-based systems (Sr-Me-Fe-O system, Me = Co, Zn, Cu, and Ni). Precursors of ferrites were prepared by polymerizable complex method. Sr₄Me₂Fe₃₆O₆₀ (Me = Co and Zn) U-type hexaferrites were synthesized at the temperature range between 1423 and 1483 K in air. Coercivity of obtained ferrite was decreased with increasing heat treatment temperatures. Cu substitution reduced formation temperature of U-type hexaferrite.

Abstract: Synthesis of Sr₃Zn₂Fe₂₄O₄₁ Z-type ferrite was investigated. Precursors of ferrite were prepared by polymerizable complex method. Identification of formed phases in the obtained samples and determination of lattice parameters of Z-type ferrite were performed by powder X-ray diffraction (XRD). Single-phase of Sr₃Zn₂Fe₂₄O₄₁ Z-type ferrite was synthesized by heating at 1463 K for 5hours in air. M-H curve of prepared single-phase Sr₃Zn₂Fe₂₄O₄₁ Z-type ferrite was measured by using vibrating sample magnetometer (VSM). It was revealed that Sr₃Zn₂Fe₂₄O₄₁ Z-type ferrite has larger saturation magnetization (23.5 μ_B/formula unit) than that of Sr₃Co₂Fe₂₄O₄₁ (22.7 μ_B/formula unit) and shows characteristic two-step saturation of magnetization as well as Sr₃Co₂Fe₂₄O₄₁ Z-type ferrite.

Abstract: Grain-oriented Bi₄Ti_2.92Nb_0.08O₁₂ (BITN) ceramics were prepared by hot-forging (HF) method. The grain orientation factor, F, of BITN ceramic determined by the Lotgering method were approximately 0.96. The resistivity, ρ, along the c-axis of HF-BITN ceramic is higher than that of the a,b-axis of HF-BITN and OF-BITN ceramics for the temperature range from 100 to 400°C. The ρ along the direction parallel to the c-axis is found to be about 10⁹ Ω·cm at 400°C, which is about ten times larger than that of OF-BITN ceramics. From resonance and anti-resonance characteristics, electromechanical coupling factor, k₂₄, was 0.026 at room temperature.

Abstract: Porous potassium niobate (KNbO₃, KN) system ceramics were prepared by spark plasma sintering (SPS) method using carbon black (CB, 5 μm). First, the powders of raw materials were mixed in ethanol by ball milling, and then calcined. Obtained KN powders with CB were sintered by SPS in argon atmosphere. Their piezoelectric properties were measured and a relationship between porosity, pore size, and sensor properties was studied. It was found that d₃₃ increased as pore size decreased. Thus, pore size was important for the improvement of value of g₃₃/ρ.

Abstract: The mechanism of pryoelectric-induced X-ray emission in LaTiO₃ crystals is discussed. It is suggested that electrons which contribute to the X-ray emission were generated around and close to the crystal and were emitted from the z surface. The poor reproducibility was found to be due to a creeping electrostatic discharge. It is speculated that one of the factors of the discharge is the accumulation of positive charges on the z surface.

Abstract: Transparent titania coating was formed onto a flexible polycarbonate plastic substrate by low-temperature fabrication process below 100 °C consisting of a sol-gel technique and a hot water treatment method. The titania coating with high transparency showed a good photocatalytic activity under ultraviolet (UV) light irradiation. Palladium metal acts as a catalyst for dissociative adsorption of hydrogen gas at room temperature under an atmospheric pressure. The palladium catalyst was deposited on the photocatalytic titania coating by a photodeposition process at room temperature under UV-light irradiation. The flexible polycarbonate plastic sheet with semitransparent palladium-deposited titania coating works as an optically readable hydrogen gas sensor which can operate at room temperature.

Abstract: Hollandite-type Mn oxides were synthesized by a co-precipitation (CP) and a hydrothermal (HT) method as the cathode catalysts for anion-exchange membrane fuel cells (AEMFCs), and their oxygen reduction reaction (ORR) activities and AEMFC single cell performances were evaluated. In this study, we prepared two kinds of hollandite oxides K_0.14MnO₂·0.12H₂O(KMO-CP) and K_0.12MnO₂·0.06H₂O(KMO-HT) and their partially Co-substituted ones K_0.11(Mn_0.88 Co_0.12)O₂・0.16H₂O(KMC_0.12-CP) and K_0.11(Mn_0.88Co_0.12)O₂· 0.08H₂O(KMC_0.12-HT), and examined the ORR activities with a rotating ring-disk electrode (RRDE) in 0.1 M KOH at 50°C. All the samples showed high onset potentials of ORR, ca. 0.9 V vs. reversible hydrogen electrode (RHE), and relatively high ORR currents at 0.75 V and high efficiencies for 4-electron reduction (Eff₄) of around 90% were obtained for the HT samples owing to higher crystallinity and higher specific surface area than those of the CP ones. The AEMFC single cells prepared with KMO-HT and KMC_0.12-HT cathode catalysts were operated stably and exhibited the maximum power densities of ca. 49 and 42 mW cm^-2, respectively, which were comparable to that of the single cell using a conventional 50 wt% Ag/C catalyst.

Abstract: Oxygen diffusivity in strontium titanate films with intentional non-stoichiometry, Sr_1+xTi_1+yO_δ with (1+x)/(1+y) = 0.71.5, was studied to reveal degradation behavior of Sr_1+xTi_1+yO_δ films. In order to utilize isotope tracer diffusion measurement, so-called gas/solid exchange method using ¹⁸O₂ gas, at relatively low temperature, very thin YSZ layer deposited on top of Sr_1+xTi_1+yO_δ film was used as catalyst for enhanced ¹⁸O[gas]/¹⁶O[solid] exchange at lower temperature. As a result, very high oxygen diffusivity at 673 K in Sr_1+xTi_1+yO_δ films with (1+x)/(1+y)>>1 was observed.

Abstract: We investigated the effect of Zr impurities on the oxygen diffusion pathway in BaTiO₃ ceramics by using an ion-imaging technique. Zr impurities were introduced into BaTiO₃ ceramics by a planetary ball milling process. The oxygen tracer diffused quickly from the surface up to the grain boundary and then appeared as discontinuous steps at the grain boundary. The results indicate that the grain boundary acted as a blocking layer against oxygen diffusion. The blocking for oxygen diffusion at the grain boundary is thought to originate during the formation and distribution of complex defects between the charged oxygen vacancies and the Ba vacancies near the grain boundary.