Pure and SbI3 doped Bi2Te3 crystals were grown by the gas phase crystal growth technique. It was found that the source materials grew into crystals in the shape of a truncated rhombohedron, and that SbI3 acted as a transport agent. Laue back reflection experiment revealed that the crystals grew in the hexagonal c-direction and that the grown crystals includes a number of single crystal lattices grown in slightly different directions within 2°.
Homogeneous Pb1-xSnxTe crystals with x=0.10, 0.15, 0.25, 0.50 were successfully grown by a new method in that the furnace was being rocked during cooling down under a unidirectional temperature gradient as well as melting. Thermoelectric properties at room temperature were examined as a function of x. They were analyzed on the basis of the Kane model. It was found that reduced the Fermi energy and the effective mass were Proportional to x up to 0.25. Temperature dependence of the thermal conductivity was calculated from the measured value of thermal conductivity at room temperature, approximating that the lattice thermal conductivity is proportional to T-1. Temperature dependence of the figure-of-merit was estimated from the calculated value of thermal conductivity and the measured ones of resistivity and thermoelectric power. From these results, the optimum combination of Pb1-xSnxTe crystals for power generation were determined for the temperature range from 300 to 800K. The combination was x=0.15, 0.25 and 0.50 forming 3-step FGM. The maximum energy conversion efficiency was 27% larger than that of the homogeneous Pb0.50Sn0.50Te. It was also confirmed that sufficient FGM effects on power generation can be realized even by 2-step FGM.
Effects of Al or Cu addition on sintering behavior, phase transformation during sintering and thermoelectric properties of β-FeSi2 were investigated. Al addition narrowed down the temperature range where the β phase was stable. In the sintering of the samples with Al addition before mechanically ground (MG), liquid phase of Al was not formed. In the case of Al addition after MG, Al-Si eutectic liquid was formed around 850K. However, the liquid phase formation caused remarkable swelling of the compacts. When Cu was added to FeSi2 powder, Cu-Si eutectic liquid was formed around 1075K during heating. The liquid phase formation was quite effective for the compound densification. Cu addition caused a rapid transformation to the β phase around 1100K during cooling. From these results, it is evident that Cu addition enables a densely sintered β-FeSi2 compound to be synthesized through the sintering only, without a conventional heat treatment for the β phase formation. The thermoelectric power and electrical resistivity of the samples with Cu addition were improved with increasing Cu content. The maximum value of the figure of merit, which is almost same as the hot-pressed samples, was obtained for the sample with 4 mass% Cu addition.
Thermoelectric figure of merit of AgBiTe2 -Ag2Te composites is increased by scattering efficiently long-wavelength phonons1, 2 at the boundaries between AgBiTe2 and Ag2Te. We prepared AgBiTe2 alloys dispersed with Ag2Te grains of (AgBiTe2)1-x(Ag2Te)x(0<x<1). Electrical conductivity, Seebeck coefficient, and thermal conductivity of AgBiTe2-Ag2Te composites depended on contents, sizes and textures of Ag2Te grains. Comparing the experimental values with the calculated values based on conductivity equation3, 4, 5, 6 with no phonon and electron scattering at the boundaries, we have found that the thermoelectric figure of merit has the maximum when the Ag2Te grain size is around 10μm, when the phonon scattering is larger than electron scattering.
In order to reconstruct a three dimensional image such as MRI, CT and confocal image from series of cross-sectional images, it was desirable to set an objective threshold at each x-y image and along z-axis. However it was not so easy to set the adequate threshold from noisy or low contrast images. In this case it sometimes used to set the threshold manually by experienced eye. The manual operation was restricted in case of the numerous data. In this study, we applied the algorithm developed by Otsu (DTSM) for the selection of the objective threshold in combination with the algorithm of Maximum Intensity Projection (MIP) and/or Average Intensity Projection(AIP). As a result the combination of AIP-DTSM gave the reasonable threshold to provide the good 3-D images.