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Silica‐bonded porous SiC ceramics were fabricated using nano‐β‐SiC powder‐carbon black template compacts by sintering in air at 600°C‐1200°C. The intrinsic microstructures of the porous ceramics were characterized by high‐resolution transmission electron microscopy, which led to the following observations: (a) a core (SiC)‐shell (SiO2) structure was formed, owing to the partial oxidation of nano‐SiC particles during sintering; (b) a low‐temperature (800°C) β‐to‐α polytypic phase transformation was observed, owing to the oxidation‐induced residual thermal stresses; and (c) non‐graphitic carbons were precipitated inside the SiC core, owing to the segregation of C atoms emitted at the strained SiC‐SiO2 interface. [ABSTRACT FROM AUTHOR]

In this work, the influence of starting particle size and sintering conditions on the microstructures and dielectric properties of BaTiO3‐based ceramics coated with 0.3Bi(Zn1/2Ti1/2)O3‐0.7BaTiO3 were investigated to reveal the core‐shell structure by using high resolution transmission electron microscopy technique coupled with energy‐dispersive spectrometer analysis. The ion‐diffusion behavior plays a critical role in the formation and evolution of the core‐shell structure and, therefore, significantly influences the dielectric properties. When using starting powders containing BaTiO3 particles larger than 100 nm in size and sintering for shorter dwelling times (0.5‐2.0 hours), a core‐shell structure could be formed and retained owing to the limited diffusion behavior, enabling BaTiO3‐based ceramics to meet the X8R specification for multilayer ceramic capacitors applications at high temperatures. However, when using 80 nm BaTiO3 nanopowders and further extending the dwelling time to 6.0 hours, more driving energy was provided to prompt ion diffusion, which led to the compositional inhomogeneity becoming homogenized. [ABSTRACT FROM AUTHOR]

The sinterability of high-purity, nanocrystalline Y2O3 without any additives was investigated by spark plasma sintering (SPS) for a combination of low sintering temperatures (850°-1050°C) and low heating rates (2-50°C/min). At a sintering temperature of 950°C and a heating rate of 2°C/min, the SPS yielded a polycrystalline Y2O3 having a relative density of 99% and an average grain size of 190 nm. The Y2O3 bodies sintered at 950° and 1050°C for 1h at the heating rate of 2°C/min exhibited an in-line transmittance of 6%-46% in a wavelength range of 400-800 nm. A high-resolution transmission electron microscopy observation and chemical analysis by an energy-dispersive X-ray spectrometer revealed that the sintered Y2O3 bodies were single-phase materials without any grain-boundary amorphous layer or impurity contamination. An isothermal SPS experiment indicated that the grain-boundary mobility is significantly enhanced by the SPS. An electron energy loss spectrometry indicated that SPS changed atomic configuration of the grain boundaries. The improved sinterability of Y2O3 is attributed to the enhanced diffusion that arises from defect reactions activated by the SPS. [ABSTRACT FROM AUTHOR]

The low-temperature alkoxide-hydroxide precipitation synthesis of nanosized crystalline barium titanate (BaTiO3) in nonaqueous media is presented. In this report, we show the influence of the reaction medium on the nature of the product by investigating the reaction of titanium (IV) isopropoxide with barium hydroxide hydrates in 2-methoxyethanol and benzyl alcohol, respectively. A perovskite phase precipitated only in benzyl alcohol, but not in 2-methoxyethanol. One molar equivalent of water, present in barium hydroxide monohydrate, was sufficient to hydrolyze the alkoxide and form nanocrystalline BaTiO3. Depending on the water concentration, the process led directly to crystalline powder of particle sizes ranging from 3 to 10 nm, and with a clear correlation between particle size and amount of water. [ABSTRACT FROM AUTHOR]

FIB-nanotomography (FIB-nt) is applied to record high-resolution 3D pore networks from cementitious materials. Based on these data, it is examined as to why the pore size distribution (PSD), which is obtained from traditional analysis by mercury intrusion porosimetry (MIP), principally deviates from the findings that are achieved by common back-scattered electron image analysis. The paper does not reflect the vulnerability of the physical model assumptions, but merely focuses on the fundamental issues of the geometrical definition of a PSD. A computationally fast approach for the PSD assessment from 3D data as well as for the simulation of MIP is presented and the varying concepts for the definition of a PSD are compared with each other. [ABSTRACT FROM AUTHOR]

Cation ordering and domain boundaries in perovskite Ca[(Mg1/3Ta2/3)1− xTi x]O3 ( x=0.1, 0.2, 0.3) microwave dielectric ceramics were investigated by high-resolution transmission electron microscopy (HRTEM) and Rietveld analysis. The variation of ordering structure with Ti substitution was revealed together with the formation mechanism of ordering domains. When x=0.1, the ceramics were composed of 1:2 and 1:1 ordered domains and a disordered matrix. The 1:2 cation ordering could still exist until x=0.2 but the 1:1 ordering disappeared. Neither 1:2 nor 1:1 cation ordering could exist at x=0.3. The space charge model was used to explain the cation ordering change from 1:2 to 1:1 and then to disorder. A comparison between the space charge model and random layer model was also conducted. HRTEM observations showed an antiphase boundary inclined to the (111) c plane with a projected displacement vector in the 〈001〉 c direction and ferroelastic domain boundaries parallel to the 〈100〉 c direction. [ABSTRACT FROM AUTHOR]

This paper describes the evolution of a sol–gel-derived PbZr xTi1− xO3 film microstructure and ferroelectricity as a function of thickness in the 0.2–1.2 μm range. In particular, we concentrate on the pyrochlore (Py) content in the film studied by the quantitative analysis of HRSEM images and corresponding ferroelectric properties. We have found that the Py content decreases with increasing thickness and have explained this phenomenon by a different extent of lead loss during processing. The ferroelectric hysteresis and fatigue of the films are correlated with the Py content. This paper shows that the Py presence in the film is responsible for the thickness-dependence of the coercive field. [ABSTRACT FROM AUTHOR]

A series of undoped and doped barium titanate powders were prepared and examined by: X-ray diffraction, high-resolution scanning electron microscopy, transmission electron microscopy, particle size, ζ-potential, specific surface area, differential scanning calorimetry (DSC), impedance spectroscopy, and secondary-ion mass spectrometry. The doped samples were prepared by two different methods: (1) coating powders with chlorides and (2) mixing chlorides in a hydrothermal reactor. Different distribution profiles of the dopant atoms were observed for the two incorporation methods. Two TC peaks were detected by DSC for samples doped by coating. Analysis of electrical measurements revealed time constant distributions that were more spread in samples that had a core–shell structure. [ABSTRACT FROM AUTHOR]

The compositions of the grains and the grain boundaries in CaCu3Ti4O12 (CCTO) have been characterized by a high-resolution field emission transmission electron microscope equipped with a high-angle annular-dark-field detector and energy-dispersive X-ray spectroscopy (EDS). The excess ions and their clusters at grain boundaries led to the observed strain contrast. These ions are further clarified as Cu ions by Z-contrast (Z: atomic number) image and EDS. The quantitative EDS analyses further indicate that the grain boundaries of CCTO are Cu rich and the grains are Cu deficient. The Ca- or Ti-rich amorphous phases were observed at corners or edges of the grains of CCTO. [ABSTRACT FROM AUTHOR]