The (1−x)NaNbO 3 -(x)NaTaO 3 solid solution was investigated for x ≤ 0.4 in terms of new high-temperature and high-permittivity dielectric system that is suitable for base metal inner electrode capacitor applications. The addition of Ta significantly enhanced the resistivity of the dielectric, resulting in superior resistivity than the dielectrics-formulated BaTiO 3 systems that dominate the multilayer ceramic capacitor dielectric devices. The voltage dependence of the permittivity was also superior to BaTiO 3 -based materials, providing higher capacitance at higher temperatures. A transmission electron microscopy study illustrated that the grains had so-called core-shell structure. According to the electron diffraction analysis, the core region had an inhomogeneous structure between antiferroelectric and ferroelectric phases, and shell region had an incommensurate ferroelectric-like structure. The core and shell region had Nb-and Ta-rich composition, respectively, and their interface was compositionally sharp, implying that shell region was formed via a liquid phase during the sintering process with an incongruent Ta dissolution reprecipitation. We anticipate that these or similar materials based on the alkali-niobate perovskites can be further enhanced to provide capacitor solutions from 150°C to 250°C, which is an important range for a number of new AC-DC invertor and engine control units.
The formation of iridium (Ir) wires of single-atom width during the contact and subsequent retraction of two nanometer-sized Ir tips was observed by in situ transmission electron microscopy with simultaneous measurements of conductance and force. The Ir wires, composed of a few atoms, grew straight along the retraction direction with an interatomic distance of 0.21–0.30 nm. The mechanical properties, i.e., elastic limit, Young's modulus and strength, of individual Ir wires were analyzed on the basis of the mechanics of materials on an atomic scale. It was found that in contrast to coarse-grained Ir crystals, the strength and elastic limit of the single-atom-width Ir wires increased to 25±17 GPa and 0.21±0.04, respectively, while Young's modulus decreased to 90±55 GPa. The conductance of the Ir wires at room temperature ranged from 0.2–3.0G
0 (G
0=2e
2/h, where e is the charge of an electron and h is Planck's constant), even for the same width, a single atom.
We investigated the mechanism of hydrothermal synthesis of BaTiO3 in the system of Ba(OH)2 and TiO2 in the early growth stage, based on model experiments using various single-crystal rutile TiO2 substrates with (001), (110), (100), and (101) orientations as starting reactants and a practical case study of widely utilized anatase TiO2 powder. The BaTiO3 products represented heterogeneous island growth directly on rutile TiO2 substrates and morphological features depending on the surface orientations of the substrates. Well-defined orientation relationships between BaTiO3 and the TiO2 substrate depended on the surface crystal planes of rutile TiO2 and were classified into four independent crystallographic types, including the unique topotaxial relationship already reported in barium diffusion-induced solid-state reactions. The hydrothermally treated anatase powder exhibited a dumbbell-like precipitation of BaTiO3 on the anatase TiO2 particles, preserving a crystallographic relationship of (001)[100] BaTiO3 ∥ (001)[100] anatase. The experimental findings revealed the heterogeneous dissolution–precipitation mechanism via surface orientation-dependent epitaxial growth of BaTiO3 directly on rutile and anatase TiO2 in the initial stage of hydrothermal reactions, suggesting the importance of controlling surface morphology and crystallinity of TiO2 as hydrothermal synthesis sources.
The oxygen diffusivity in BaTiO 3 thin films heteroepitaxially grown on SrTiO 3 substrates was investigated using a gas/solid exchange technique with 18 O-isotope-enriched gas. Deformation of the BaTiO 3 lattice and inhibition of the oxygen diffusivity occurred simultaneously when the YSZ layer, which is assumed to be catalytic for the 18 O/ 16 O exchange reaction, was deposited on BaTiO 3 . The mechanism for the reduction in oxygen diffusivity due to the YSZ cover layer is discussed in terms of residual stress in the strained BaTiO 3 layer.
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