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We report on the detection of electric field-induced second harmonic generation (EFISHG) from the anode interfaces of reduced and oxidized Fe-doped SrTiO3 (Fe:STO) single crystals. For the reduced crystal, we observe steady enhancements of the susceptibility components as the imposed dc-voltage increases. The enhancements are attributed to a field-stabilized electrostriction, leading to Fe:Ti-O bond stretching and bending in Fe:Ti-O6 octahedra. For the oxidized crystal, no obvious structural changes are observed below 16 kV/cm. Above 16 kV/cm, a sharp enhancement of the susceptibilities occurs due to local electrostrictive deformations in response to oxygen vacancy migrations away from the anode. Differences between the reduced and oxidized crystals are explained by their relative oxygen vacancy and free carrier concentrations which alter internal electric fields present at the Pt/Fe:STO interfaces. Our results show that the optical SHG technique is a powerful tool for detecting structural changes near perovskite-based oxide interfaces due to field-driven oxygen vacancy migration. [ABSTRACT FROM AUTHOR]

This paper demonstrates that fine-grained (2–3 μm), transparent Nd:YAG can be achieved at SiO2 doping levels as low as 0.02 wt% by the sinter plus hot isostatic pressing (HIP) approach. Fine grain size is assured by sintering to 98% density, in order to limit grain growth, followed by HIP. Unlike dry-pressed samples, tape-cast samples were free of large, agglomerate-related pores after sintering, and thus high transparency (i.e., >80% transmission at 1064 nm) could be achieved by HIP at <1750°C along with lower silica levels, thereby avoiding conditions shown to cause exaggerated grain growth. Grain growth was substantially limited at lower SiO2 levels because silica is soluble in the YAG lattice up to ∼0.02–0.1 wt% at 1750°C, thus allowing sintering and grain growth to occur by solid-state diffusional processes. In contrast, liquid phase enhanced densification and grain growth occur at ∼0.08–0.14 wt% SiO2, especially at higher temperatures, because the SiO2 solubility limit is exceeded. [ABSTRACT FROM AUTHOR]

Microstructural control in thin-layer multilayer ceramic capacitors (MLCCs) is one of the present-day challenges for maintaining an increase in capacitive volumetric efficiency. The present paper continues a series of investigations aimed at understanding and controlling the microstructural stability of ultrathin Ni electrodes in MLCCs. Here, a kinetic approach based on the control of sintering profiles is used. Ni–BaTiO3 MLCC chips (0805-type with 300 active layers) are nonisothermally sintered up to 900°–1300°C with different heating rates in the range from 200° to 3000°C/h. In general, the continuity of the Ni electrodes increases with heating rate. However, a strong nonlinear dependence of Ni electrode continuity on sintering temperature is observed. It is concluded that a low-melting interfacial liquid (Ni,Ba,Ti) alloy layer initiates at temperatures between 1000° and 1100°C when the Ni electrodes are under tension. This interfacial liquid phase accelerates a stress-induced diffusion and is the key cause of the severe electrode discontinuities during heating. At higher temperatures (above 1100°C), where compressive stresses are active, the interfacial liquid alloy layer facilitates some recovery of the Ni electrode microstructure. The formation of the interfacial liquid alloy layer can be kinetically controlled using fast-heating rates, which improves the Ni electrode continuity. [ABSTRACT FROM AUTHOR]

A novel approach to pressureless sintering based on the combination of rapid-rate sintering, rate-controlled sintering, and two-step sintering under a controlled atmosphere is proposed. This combined sintering method facilitates control of grain and pore morphology. The application of this sintering approach for pure nanocrystalline barium titanate powder enables the suppression of grain growth during the intermediate and final stages of sintering and the production of fully dense ceramics with 108 nm grain size. The grain growth factor is 3.5, which is three and 17 times smaller than rate-controlled and conventional sintering, respectively. [ABSTRACT FROM AUTHOR]

Ceramic/metal interfaces have vast technological significance and are used in a variety of applications. This has prompted a concerted effort to develop fundamental structure/property relationships for these structures. This article critically reviews recent advances in complementary experimental and theoretical studies of ceramic/metal interfaces to provide an overview of progress made towards developing these relationships. In particular, the focus is on the structure, characterization, and modeling of non-reactive, bulk ceramic/metal interfaces. This includes determining interface atomic structure and chemistry and investigating impurity segregation to the interfaces. Additionally, the most important advances in the experimental and theoretical modeling of interfacial structure and chemistry are reviewed and comments are provided on the future outlook of this field. [Copyright &y& Elsevier]

Color center formation was studied in vacuum sintered Nd3xY3-3xAl5O12 transparent ceramics. The primary color centers were F- and F+-centers as evidenced by optical absorption in the 250-400 nm wavelength range and the presence of an electron spin resonance (ESR) line at g=1.9977. Annealing in air at 1600 °C for 10 h reduced the number of color centers to below the detection limit of ESR. Color center formation is controlled by oxidation and reduction of Fe2+/3+ impurities. [ABSTRACT FROM AUTHOR]

Abstract: Surface layers of the pseudo-binary eutectic comprised of boron carbide (B4C) and titanium diboride (TiB2) were directionally solidified via direct laser irradiation in an argon atmosphere. The resulting surface eutectic layers had highly oriented lamellar microstructures, whose scale (i.e. interlamellar spacing) was controlled directly by the laser scan rate, following an inverse square root dependence for lower solidification velocities. Higher velocities (>∼4.2mm/s) departed from this relationship, although well-ordered microstructures were still achieved. A concomitant increase in the Vickers hardness with decreasing interlamellar spacing was observed, although the trend did not correspond to traditional Hall–Petch behavior. The hardness of the eutectic composites became load-independent at indenter loads greater than 9.81N, indicating a potential transition from plastic to fractural deformation during indentation. A Vickers hardness of 32GPa was achieved in the highest solidification velocity samples (42mm/s) which had interlamellar spacings of 180nm. [Copyright &y& Elsevier]