Dong-Hi Lee

Characteristics of thin-film thermoelectric devices for power generation

The characteristics of flash-deposited and thin-film thermoelectric generators are described. The overall Seebeck coefficient for a single couple in the generator ( forming the n-type thermoelement and forming the p-type element) is . This value approaches the figures presented for these materials in bulk form. The results demonstrate how the parameters of the generator can be altered in order to maximize generation efficiency. For example, doubling the cross sectional area of the thermoelement can result in a two-fold increase in the output power. Extrapolation of the results indicates that a generator of dimensions can provide a voltage source sufficiently powerful to drive a microelectronic circuit (namely 3 - 5 V at about ). Hence, potentially, the generator could be used in place of a battery unit in small-scale generation applications, where a source of waste heat is available.

Thin film thermoelectric generator cell of Bi-Sb-Te-Se system

Thin film thermoelectric generator cells (TFTEGCs) of the Bi-Sb-Te-Se system were fabricated and their performances were investigated. The generator cells were composed of several layers of plate-modules, and each plate-module contained 15 p/n couples and was connected electrically in series or in parallel. Variations of the open circuit voltage, short circuit current and maximum output power as a function of temperature difference showed a linear relationship for the first two values, but there was a second-order relationship for the latter. The output power produced per couple and per unit temperature difference was a 3.5 nW/K couple.

Thermoelectric properties of Co-doped n-type iron silicides prepared by mechanical alloying

N-type thermoelectrics of Co-doped iron silicide have been fabricated and studied. The Fe:Co ratio was kept constant at 0.95:0.05 to achieve a composition of (Fe/sub 0.95/Co/sub 0.05/)/sub x/Si/sub 2/, where two values of x were chosen: 0.9 and 0.8 to observe the dispersion effect of the Si phase. For these, the mechanical alloying method for powdering and the pressure-resistance-sintering were employed. The sintering temperature, inherently controlling the size of dispersed Si phases, was varied from 760 to 880/spl deg/C. The sintered specimens of the present process showed a similar Seebeck coefficient (a/spl ap/183 /spl mu/V/K) compared to the ordinary ingot powdering method. The electrical and thermal conductivities, however, decreased with the reduction in interspacing of Si phases. The figure of merit was increased to Z=1.0/spl times/10/sup -4//K, which was believed to be enhanced by the phonon scattering effect of the dispersed Si phases.

Diffusion at p/n junctions of thin film Bi0.5Sb1.5Te3/Bi2Te2.4Se0.6 thermoelectrics

Whatever the methods for preparation of thin film thermoelectrics, a subsequent annealing is inevitable to reduce defects and residual stresses introduced during the fabrication processes and also to control the uniform carrier concentration of the film. The diffusion‐induced atomic redistribution and broadening of p/n junction region are expected to affect thermoelectric properties of thin film modules thereafter. In the present studies, it has been intended to investigate the diffusion at p/n junctions of thermoelectric thin films and to relate it with the property changes. For this, thermoelectric thin film junctions were prepared by the flash evaporation technique. P‐ and n‐type materials used were Bi0.5Sb1.5Te3 and Bi2Te2.4Se0.6, respectively. Aluminum thin layer employed as a diffusion barrier between p‐ and n‐type films of the junction was found to be an effective barrier by showing a negligible diffusion into both type films. Thermoelectric properties of p/n couples incorporated with aluminum barr...Whatever the methods for preparation of thin film thermoelectrics, a subsequent annealing is inevitable to reduce defects and residual stresses introduced during the fabrication processes and also to control the uniform carrier concentration of the film. The diffusion-induced atomic redistribution and broadening of {ital p}/{ital n} junction region are expected to affect thermoelectric properties of thin film modules thereafter. In the present studies, it has been intended to investigate the diffusion at {ital p}/{ital n} junctions of thermoelectric thin films and to relate it with the property changes. For this, thermoelectric thin film junctions were prepared by the flash evaporation technique. {ital P}- and {ital n}-type materials used were Bi{sub 0.5}Sb{sub 1.5}Te{sub 3} and Bi{sub 2}Te{sub 2.4}Se{sub 0.6}, respectively. Aluminum thin layer employed as a diffusion barrier between {ital p}- and {ital n}-type films of the junction was found to be an effective barrier by showing a negligible diffusion into both type films. Thermoelectric properties of {ital p}/{ital n} couples incorporated with aluminum barrier layer were accordingly retained without any deterioration, when compared with the ``virgin`` junctions. {copyright} {ital 1995} {ital American} {ital Institute} {ital of} {ital Physics}.

Effect of dispersed Si-phase on thermoelectric properties of FeSi/sub 2/ prepared by mechanical alloying and sintering

While melt-cast FeSi/sub 2/ requires careful heat-treatment of homogenization and phase transformation to achieve thermoelectric /spl beta/-phase, the mechanical alloying(M/A) and sintering method is expected to simplify the process, By using the M/A method with elementary Fe and Si coarse powders, very fine powders consisting of FeSi- and Si-phases were obtained. Especially when excess Si was deliberately introduced in the starting materials, the desired microstructure containing finely distributed Si-phase in the matrix of /spl beta/-FeSi/sub 2/ was produced by subsequent sintering. The volume fraction of dispersed Si-phase could be controlled within a range of 0.26-0.38 by varying the excess Si content. The shape of the dispersed the Si phase was something like the coral colony of fine finger-shaped protrusions (diameter /spl les/0.5 /spl mu/m and length /spl les/3 /spl mu/m). The size and volume fraction of the Si-phase in the /spl beta/-FeSi/sub 2/ matrix was analysed being effective in controlling the thermal conductivity of the sintered mass due to the phonon scattering.

Fabrication and characterization of Bi/sub 2/Te/sub 3/-Sb/sub 2/Te/sub 3/ based thermoelectric materials by powder-extrusion-sintering technique

Despite high thermoelectric performance, the commercial applications of Bi/sub 2/Te/sub 3/-Sb/sub 2/Te/sub 3/ based thermoelectrics are limited mainly because of production cost due to complicated processing steps. In this study, a new approach to the powder-extrusion-sintering method, which is intended to fabricate a sound sintered material by the simultaneous application of pressure and heat, was investigated. This method is expected to be suitable for low cost production of Bi/sub 2/Te/sub 3/-Sb/sub 2/Te/sub 3/ materials because of the possibility of semi-continuous fabrication processing. It was possible to achieve high density (/spl ges/95% of theoretical density) products by adjusting variables, such as; die angle, die hole length, powder size, extrusion pressure and temperature. Thermoelectric properties of sintered specimens were measured, and discussed to achieve optimum fabrication conditions.

Preparation and characterization of thermoelectric /spl beta/-FeSi 2 phase dispersed with Si

Heat treatment of a single phase of Fe-Si system produced eutectoid microstructures consisted of /spl beta/ and Si phases. The volume fraction of Si dispersoids, 0.1/spl sim/0.25 /spl mu/m in size, was controlled by varying Si content within the compositional range of /spl alpha/ single phase. The dispersed Si particles in the /spl beta/ matrix acted as effective scattering centers for carriers as well as phonons.