High performance Bi2Te3 bulk materials with layered nanostructure have been prepared by combining melt spinning technique with spark plasma sintering, and their thermoelectric transport properties are investigated. The electrical conductivity increases greatly and the lattice thermal conductivity decreases significantly with the increase of the roller’s linear speed. These lead to a great improvement in the thermoelectric figure of merit (ZT). The maximum ZT value of 1.35 is obtained at 300K for the sample which is prepared by melt spinning with roller linear speed of 40m∕s. Compared with the zone melting sample, it increases by 73% at the same temperature.

Space planes require high-performance heat-resistant materials which can withstand ultrahigh temperatures and extremely large temperature gradients. To meet these needs, functionally gradient materials (FGMs) were proposed about 10 years ago in Japan.Figure 1 shows a conceptual diagram of functionally gradient materials, taking into account the relaxation of thermal stress. For the surface that contacts high-temperature gases at thousands of degrees, ceramics are used to provide adequate heat resistance. For the surface that provides cooling, metallic materials are used to furnish the necessary thermal conductivity and mechanical strength. In addition, the composition of these materials is formulated to provide optimum distribution of composition, structure, and porosity to effectively relax thermal stress.Since fiscal 1987, an R&D project entitled “Research on Fundamental Techniques to Develop Functionally Gradient Materials for Relaxation of Thermal Stress,” which aimed to develop ultra heat-resistant materials, had been carried out with special coordination funds from the Science and Technology Agency. The five-year project had two phases; Phase I was carried out from 1987 to 1989, and Phase II from 1990 to 1991.

Recently, spaceplanes such as "Orient Express" projected by the United States are attracting attention as newspace transportation media. In Japan also, the study for developing spaceplanes is recognized as one of the most infiuential programs among the various research and development projects.

Thermoelectric technology can be another direct way to convert solar radiation into electricity, using the Seebeck effect. Herein, a prototype concentration solar thermoelectric generator (CTG) and a discrete numerical model for the evaluation of the whole system are presented. The model takes into account the temperature dependence of the thermoelectric material properties by dividing the thermoelectric leg into finite elements and is proved to be more accurate for calculation of the conversion efficiency of the thermoelectric modules when large temperature gradients occur in the CTG system. Based on the best available properties of various bulk thermoelectric materials reported in the literature, the best possible performance of the CTG system is predicted, and the CTG system design, including the selection of the concentration ratio and the cooling method for different thermoelectric materials, are discussed in detail.

Single-phase CamCenFexCo4−xSb12 compounds filled by Ca and Ce were synthesized by using melting-quench-diffusion annealing reaction method. The structure and thermoelectric properties of double atoms filled skutterudite compounds were investigated. The results of Rietveld refinement indicate high reliabilities of filling fractions consistent with the inductively coupled plasma atomic emission spectrometry (ICP-AES) analysis, CamCenFexCo4−xSb12 compounds possess skutterudite structure, and Sb-icosahedron voids were filled with Ca or Ce. The thermal parameter BCa∕Ce (6.0) of Ca∕Ce is much larger than that of BSb (0.3) and BFe∕Co (0.3) of Sb and Fe∕Co. The specific chemical states of atoms were obtained from x-ray photoelectron spectroscopy quantitative analysis, which shows that Sb has five chemical states and the relative content is correlative with the total filling fraction; the filling atoms have three filling positions and tend to fill the center position of the Sb-icosahedron voids, preferentially. With the same filling fraction, carrier concentration and electrical conductivity of p-type CamCenFexCo4−xSb12 are intervenient between that of single atom filled compounds CamFexCo4−xSb12 and CenFexCo4−xSb12, and decreased with increasing Ca and Ce, especially Ce, filling fraction. The Seebeck coefficients are increased with increasing total filling fraction, and the influence of Ce filling fraction to the Seebeck coefficients is more notable than that of Ca, and with the same filling fraction, the lattice thermal conductivity of CamCenFexCo4−xSb12 is smaller than that of CamFexCo4−xSb12 and CenFexCo4−xSb12; furthermore, when the total filling fraction (m+n) is about 0.3 and the respective filling fraction of Ca and Ce is approximately identical, the lattice thermal conductivity reached the minimum value. The greatest ZT value of 1.2 was obtained at 750K for p-type Ca0.18Ce0.12Fe1.45Co2.55Sb12 compound.