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Abstract Intensive efforts to engineer the microstructures of materials by utilizing atomic-scale defects have been made to overcome the current limitation on physical properties such as thermoelectric energy conversion performance levels (ZT). Here, we report that (i) internally dispersed strains are generated by a nano-diamond (ND) inserted into polycrystalline Bi-Sb-Te (BST) alloys, which thereby create point-defects clustered zones (PDZs) around the ND/BST interface; (ii) a local strain field is also generated, wherein many point defects are intensified; (iii) locally-strained interfaces result in an increase of the hole carrier concentration caused by the formation of cationic defects. From these results, strain-mediated point defects in ND particle-dispersed BST matrix (ND/BST) composites are assessed as artificial nanostructures, which can independently control transport properties of carriers and phonons. Our findings open new avenues for design and applications of favorable atomic-defect-structures in the area of energy or electronic materials through a classical solid-state sintering method. Graphical abstract fx1 Highlights • Dispersed nanodiamonds generate locally concentrated-strain fields in the matrix. • The locally strained interfaces are corresponding to point-defects clustered zones. • Nanoscale clustering of cationic defects results in hole carrier density. • PDZ independently controls thermal conductivity and power factors for improving ZT. [ABSTRACT FROM AUTHOR]

There have been technical limitations to manufacture microstructures due to difficulty of demolding during replication process of high aspect ratio microstructure in mass production technologies. In the present study, the fabrication of a novel sacrificial micro mold insert and powder injection molding process using such a micro mold insert is proposed and developed. It utilizes a synchrotron radiation to fabricate the shape of polymer based sacrificial mold inserts and then these mold inserts were exposed at X-ray once more to adjust its solubility. This second X-ray exposure facilitates dissolving of mold inserts instead of demolding process which have difficulties like pattern collapses or defects in case of precise replication process. In this manner, severe problems of demolding process in conventional mass production technologies can be efficiently overcome. To verify the usefulness of the proposed technique, polymer based micro mold inserts with several tens of micrometer sized structure for piezoelectric sensor applications were fabricated using X-ray micromachining process radiated synchrotron. The solubility of mold inserts were optimized by the second X-ray exposure without an X-ray mask and then subsequent powder injection molding process was utilized with a piezoelectric based material. Finally, piezoelectric ceramics with micrometer-scale and high aspect ratio of 5 were successfully fabricated, verifying that the present sacrificial mold system is useful for the precise replication process such as the fabrication of microstructure with high aspect ratio or complicated structure. [ABSTRACT FROM AUTHOR]

Abstract: To achieve the surface-orientation-controlled microstructure of K0.5Na0.5NbO3, not only the template must exhibit the high anisotropy like a plate-shape but the reactive stability as well as the crystallographic coherency between the template and the K0.5Na0.5NbO3 must be carefully considered. In this work, we focused on what kinds of ceramics are suitable for the fabrication of the surface-orientation-controlled K0.5Na0.5NbO3. First of all, BaTiO3, SrTiO3, Ba(Zr0.1Ti0.9)O3, KNbO3, NaNbO3, KTaO3 and NaTaO3 were chosen as the candidates in the regard of the crystallographic coherency. To verify the chemical stability between candidate ceramics and K0.5Na0.5NbO3, the prepared candidate ceramic bulks were embedded by the K0.5Na0.5NbO3 powder, they were annealed at 1100°C, and then the interface regions between candidate ceramics and K0.5Na0.5NbO3 were investigated using Secondary Electron Microscopy (SEM) equipped with Energy Dispersive Spectrometer (EDS). From these experimental results, BaTiO3, SrTiO3, Ba(Zr0.1Ti0.9)O3, KNbO3 and NaTaO3 were found to be not appropriate for the templates for the tailoring of K0.5Na0.5NbO3, while the NaNbO3 and KTaO3 showed a good crystallographic coherency and a chemical stability with K0.5Na0.5NbO3. [Copyright &y& Elsevier]

For its analysis and understanding, sintering has been conventionally assumed to occur in proportion to driving force [J. Appl. Phys. 36 (1955) 1205; Acta Metall. 13 (1965) 227; Mater. Sci. Eng. 48 (1981) 53; Ceramic Processing and Sintering, Marcel Dekker, New York, 2003, p. 470]. This investigation, however, shows for the first time that the conventional assumption does not apply to faceted boundaries and that the microstructure can be frozen for faceted boundaries. A structural transition from rough to faceted was induced in BaTiO3, by changing oxygen partial pressure. As long as the boundary was rough, continuous grain growth and densification occurred with sintering time, in agreement with the conventional assumption. With the onset of the structural transition from rough to faceted, however, grain growth and densification rates were reduced and became zero at the completion of the transition. This result demonstrates that critical driving forces are present for grain growth and densification for faceted boundaries, unlike the conventional understanding. The result also suggests that the formation or maintenance of faceted boundaries is crucial to inhibit grain growth and thus to produce ultrafine-structured materials. [Copyright &y& Elsevier]

Abstract: A solid solution Sr2FeReO6–xRe [SFRO–xRe] system with 0wt%≤ x ≤20wt% was synthesized by conventional solid state method. With increasing the amount of Re, crystallinity of SFRO was confirmed to increase, but the addition of large amount of Re induced the formation of the second phase (Re and unknown), resulting in the solubility limit of Re into SFRO. Compared to a sample by a muffle furnace, relative density of SFRO by SPS was relatively high and increased with increasing the amount of Re. Besides, with increasing the Re content, it was found that the dense microstructure was formed with large grains, which is probably due to the liquid phase related to Re inside the sample during sintering. The magnetic property was found as a function of Re content that saturation magnetization was increased while remnant magnetization was not significant. In addition, coercive magnetic field was slightly decreased as well, reflecting the typical soft materials. Therefore, the addition of Re is strongly effective to improve microstructure and magnetic property of SFRO. [Copyright &y& Elsevier]

A dense silicon carbide (SiC) ceramic with a very high flexural strength at 2000 °C (981 ± 128 MPa) was obtained by conventional hot-pressing with extremely low additive content (2000 ppm Y 2 O 3 ). Observations using high-resolution transmission electron microscopy (HRTEM) showed that (1) homophase (SiC/SiC) boundaries were clean without an intergranular glassy phase and (2) junction pockets consisted of nanocrystalline Y-containing phase embedded in an amorphous Y-Si-O-C-N phase. The excellent strength at 2000 °C was attributed to the clean SiC/SiC boundary and the strengthening effect of plastic deformation. [ABSTRACT FROM AUTHOR]