Compositionally graded structures

An alternative to the heterostructure is also shown. In this case, a compositionally graded structure is formed where the composition x of Hgi.xCdxTe varies with the distance from the passivation layer. Methods of manufacturing such structures are discussed. 

In this study FGM samples were prepared to prove the enhancement in output characteristics by introducing compositionally graded structure. Through the study on a compositional dependence of thermoelectric properties, segmentation structure of y = 0.80 / 0.825 / 0.9 was selected where y indicated the antimony telluride fraction in (BijICj), (SbjTej) system. 

An image of a FGM collector for a thermionic converter is shown in Fig. 12. The distinctive feature of the FGM collector is that the metal oxide materials with the compositionally graded structure is coated on the metal substrate by sputtering method. At the same time the electric insulation materials with the small columnar shape are placed uniformly dispersed on the collector to hold the gap of 10 jU m between the emitter and the... 

In addition to bilayered electrodes with a functional layer and a support layer, electrodes have also been produced with multilayered or graded structures in which the composition, microstructure, or both are varied either continuously or in a series of steps across the electrode thickness to improve the cell performance compared to that of a single- or bilayered electrode. For example, triple-layer electrodes commonly utilize a functional layer with high surface area and small particle size, a second functional layer (e.g., reference [26]) or diffusion layer with high porosity and coarse structure, and a current collector layer with coarse porosity and only the electronically conductive phase (e.g., reference [27]) to improve the contact with the interconnect. 

Although the electrode performance can be improved by the introduction of compositional and microstructural gradients into the anode or cathode, the processing required to produce such graded layers also increases in complexity as the number of discrete layers increases, particularly when separate deposition and firing steps are required for each increment in layer composition or structure. 

The combination of various SOFC component performance, microstructural, and property requirements has led to a variety of structures, such as the composite, graded, and multilayered electrodes and electrolytes described above. The need... 

Guidotti C. V., Herd H. H., and Tuttle C. L. (1973). Composition and structural state of K-feldspars from K-feldspars -I- sillimanite grade rocks in northwestern Maine. Amer. Mineral, 58 705-716. 

The imager of EP-A-0406696 is made up of a compositionally graded p-type base layer and a compositionally graded cap layer in which pn-junctions are formed. The structure has a small amount of leakage current and a large diode impedance. 

STRUCTURE AND STABILITY OF COMPOSITION-GRADED TRANSITIONAL BUFFERING PHASE... 

A functionally graded material (FGM) is a material in which the composition and structure gradually change resulting in a corresponding change in the properties of the material. This FGM coneept can be applied to various materials for struetural and funetional uses. 

Simulation of the Elasto-Plastic Deformations in Compositionally Graded Metal-Ceramic Structures Mean-Field and Unit Cell Approaches ... 

The elasto plastic behavior of a compositionally graded metal-ceramic structure is investigated. The deformation under uniaxial loading is predicted using both an incremental Mori-Tanaka method and periodic as well as random microstructure extended unit cell approaches. The latter are able to give an accurate description of the local microfields within the phases. Furthermore, the random microstructure unit cell model can represent the interwoven structure at volume fractions close to 50%. Due to the high computational costs, such unit cell analyses are restricted to two-dimensional considerations. 

The deformation behavior of a compositionally graded metal-ceramic structure has been investigated by numerical and (semi)analytical simulations. Random microstructure models are able to predict the response of an FGM-structure in a more accurate way than the other approaches. The interwoven structure in the middle of the FGM can be accounted for using this modeling strategy. For the extended periodic unit cell models the predicted stress strain response depends strongly on the micro-arrangement of the inclusions. Detailed information on the microfields of the stresses and strains can only be obtained by the extended unit cell models. The incremental Mori-Tanaka method... 

Lately, the spark plasma sintering has been used gradually in practical applications. The characteristics of this new sintering process are low- temperature and short- time sintering. The features of this process are expected to solve the above problems. Therefore, we tried to sinter- bond the composition graded cemented carbide powders on steel substrate by spark plasma sintering, and evaluated the structural and mechanical properties of this composite material. This paper reports the results of these evaluations. 

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