The term photonic crystals appears because of the analogy between electron waves in crystals and the light waves in artificial periodic dielectric structures. During the recent years the investigation of one-, two-and three-dimensional periodic structures has attracted a widespread attention of the world optics community because of great potentiality of such structures in advanced applied optical fields. The interest in periodic structures has been stimulated by the fast development of semiconductor technology that now allows the fabrication of artificial structures, whose period is comparable with the wavelength of light in the visible and infrared ranges.

http://ieeexplore.ieee.org/iel5/6354/16969/00781867.pdf

Photonic crystals

Oxide pyrochlores — A review

This review article aims to provide an updated and comprehensive description of the development of the Electric Current Activated/assisted Sintering technique (ECAS) for the obtainment of dense materials including nanostructured ones. The use of ECAS for pure sintering purposes, when starting from already synthesized powders promoters, and to obtain the desired material by simultaneously performing synthesis and consolidation in one-step is reviewed. Specifically, more than a thousand papers published on this subject during the past decades are taken into account. The experimental procedures, formation mechanisms, characteristics, and functionality of a wide spectrum of dense materials fabricated by ECAS are presented. The influence of the most important operating parameters (i.e. current intensity, temperature, processing time, etc.) on product characteristics and process dynamics is reviewed for a large family of materials including ceramics, intermetallics, metal–ceramic and ceramic–ceramic composites. In this review, systems where synthesis and densification stages occur simultaneously, i.e. a fully dense product is formed immediately after reaction completion, as well as those ones for which a satisfactory densification degree is reached only by maintaining the application of the electric current once the full reaction conversion is obtained, are identified. In addition, emphasis is given to the obtainment of nanostructured dense materials due to their rapid progress and wide applications. Specifically, the effect of mechanical activation by ball milling of starting powders on ECAS process dynamics and product characteristics (i.e. density and microstructure) is analysed. The emerging theme from the large majority of the reviewed investigations is the comparison of ECAS over conventional methods including pressureless sintering, hot pressing, and others. Theoretical analysis pertaining to such technique is also proposed following the last results obtained on this topic.

Consolidation/synthesis of materials by electric current activated/assisted sintering

Along with extensive research on the three-dimensional (3D) printing of polymers and metals, 3D printing of ceramics is now the latest trend to come under the spotlight. The ability to fabricate ceramic components of arbitrarily complex shapes has been extremely challenging without 3D printing. This review focuses on the latest advances in the 3D printing of ceramics and presents the historical origins and evolution of each related technique. The main technical aspects, including feedstock properties, process control, post-treatments and energy source–material interactions, are also discussed. The technical challenges and advice about how to address these are presented. Comparisons are made between the techniques to facilitate the selection of the best ones in practical use. In addition, representative applications of the 3D printing of various types of ceramics are surveyed. Future directions are pointed out on the advancement on materials and forming mechanism for the fabrication of high-performance ceramic components.

3D printing of ceramics: A review

New microproducts need the utilization of a diversity of materials and have complicated three-dimensional (3D) microstructures with high aspect ratios. To date, many micromanufacturing processes have been developed but specific class of such processes are applicable for fabrication of functional and true 3D microcomponents/assemblies. The aptitude to process a broad range of materials and the ability to fabricate functional and geometrically complicated 3D microstructures provides the additive manufacturing (AM) processes some profits over traditional methods, such as lithography-based or micromachining approaches investigated widely in the past. In this paper, 3D micro-AM processes have been classified into three main groups, including scalable micro-AM systems, 3D direct writing, and hybrid processes, and the key processes have been reviewed comprehensively. Principle and recent progress of each 3D micro-AM process has been described, and the advantages and disadvantages of each process have been presented.

/pdf/a-review-on-3d-micro-additive-manufacturing-technologies-1kbpeb2xb5.pdf

A review on 3D micro-additive manufacturing technologies

Fully densified silicon nitride without additives was fabricated by means of hot isostatic pressing. The sintering process of highly pure powder was investigated with special interest in the evolution of α–β phase transformation, densification, and microstructure development. It was observed that the transformation occurred without a liquid phase below 1730°C, which corresponds to the melting point of SiO2. Above 1730°C, the densification and β-grain elongation accelerated concurrently because of the appearance of liquid SiO2. However, full densification was attained at 1950°C together with marked grain growth. Flexural strength, microhardness, fracture toughness, and Young's modulus of sintered bodies were measured as a function of temperature. In the sintered body started from highly pure powder, excellent MOR behavior was found up to 1400°C. Impurity content of a few hundred ppm was found to be sufficient to make densification easy and to degrade high-temperature strength.

Hot Isostatic Press Sintering and Properties of Silicon Nitride without Additives

The dense polycrystalline Ti3SiC2 has been synthesized by reactive HIPing of Ti, SiC and C powders The bulk material with the highest Ti3SiC2 content about 97 vol % was obtained when treated at 1500°C, 40 MPa for 30 min The density was 99% of the theoretical value The Ti3SiC2 grains had the columnar and plate-like shapes The grains were well boned to form a network structure Many stacking faults were observed along the (001) plane of Ti3SiC2 The Vickers hardness, Young's modulus, flexural strength and fracture toughness were 4 GPa, 283 GPa, 410 MPa and 112 MPa m1/2, respectively The Ti3SiC2 was stable up to 1100°C in air The electrical resistivity was 27 × 10−7 Ω·m at room temperature The resistivity increased linearly with the increasing temperature It may be attributed to a second order phase transition The Seebeck coefficient was from 4 to 20 μV/K in the temperature range 300–1200 K It seems that Ti3SiC2 is semi-metallic with hole carriers from this small positive value

Dense Ti3SiC2 prepared by reactive HIP

A new superconductor Sr 1- x La x CuO 2 ( x =0.1) was prepared applying high pressure synthesis. It has an infinite-layer structure and its T c equals 43 K. It is probably an electron-doped superconductor because the reductive atmosphere was critical for its preparation under high pressure.

Superconductivity in the infinite-layer compound Sr1-xLaxCuO2 prepared under high pressure

Ti3SiC2 was rapidly synthesized and simultaneously consolidated from the starting mixture of Ti/Si/2TiC by spark plasma sintering (SPS) An intensive reaction leading to the formation of Ti3SiC2 occurred at the measured temperature of around 1200 °C, which is several hundreds degrees lower than that of conventional reactive hot pressing The phase composition of the product could be tailored by adjusting the process parameters An axisymmetric preferred orientation of the Ti3SiC2 grains with well-developed (008) planes was formed, resulting in an anisotropic hardness in respect to the textured product

Rapid synthesis of dense Ti3SiC2 by spark plasma sintering

Perovskite-type (La 1-x Sr x )MnO 3 (0≤x≤0.3) was synthesized through the sol-gel process at low temperature (400 o to 500 o C). Poly(acrylic acid) (PAA) was used to make a gel from an aqueous solution of lanthanum, strontium, and manganese nitrates. The particle-diameter distribution of the manganites had a maximum value of 0.3 to 0.7 μm, and a specific surface area of about 17.5 to 23.5 m 2 /g

Yoshinari Miyamoto

Papers

Hot Isostatic Press Sintering and Properties of Silicon Nitride without Additives

Dense Ti3SiC2 prepared by reactive HIP

Superconductivity in the infinite-layer compound Sr1-xLaxCuO2 prepared under high pressure

Rapid synthesis of dense Ti3SiC2 by spark plasma sintering

Synthesis of Perovskite‐Type (La1−xSrx)MnO3 (O X 0.3) at Low Temperature