Thermoelectric material having crystal grains well oriented in certain direction and process for producing the same

Abstract

Thermoelectric material is produced through a process sequence including a liquid quenching, a primary solidification such as a hot pressing or extrusion and an upset forging; although the C-planes of the crystal grains are directed in parallel to the direction in which the force is exerted on flakes during the hot pressing / extrusion, the a-axes are randomly directed; the a-axes are oriented in a predetermined direction through the upset forging; this results in improvement of electric resistivity without reduction in the figure of merit.

Description

FIELD OF THE INVENTION [0001] This invention relates to thermoelectric material and, more particularly, to thermoelectric material and a process for producing the thermoelectric material. DESCRIPTION OF THE RELATED ART [0002] There have been known two processes for producing the thermoelectric material. The first process is illustrated in FIGS. 1A to 1C, and is hereinbelow referred to as “unidirectional solidification process”. The second process is called as “sintering process”. Description is firstly made on these two prior art processes. [0003] The prior art unidirectional solidification process starts with preparation of pellets 1 of raw material. The pellets 1 are put in a quartz cylinder, and are accumulated in one end portion of the quartz cylinder. Heat is applied to the other end portion 2a of the quartz cylinder. The other end portion 2a is melted, and is closed. The melted quartz is solidified so that the pellets 1 are sealed in the quartz capsule 2 as shown in FIG. 1A. [...

AI Technical Summary

Benefits of technology

[0019] It is therefore an important object of the present invention to provide thermoelectric material, which exhibits a large figure of merit in high-temperature ambience without increase of electric power consumption.

Problems solved by technology

A problem inherent in the thermoelectric material produced through the prior art unidirectional solidification process is brittleness.

Another problem is a low figure of merit.

However, the fine powder has reached the limit.

It is impossible to perfectly prevent the powder particles from the oxidation.

Thus, the small figure of merit is also the serious problem in the thermoelectric material produced through the prior art sintering process.

However, the crystal grains are randomly grown so that the crystal becomes much poorer than the crystal before the annealing / high-temperature shaping process.

Thus, the counter-measure proposed in Japanese Patent Application laid-open No. 10-178219 is less effective against the small figure of merit.

However, the prior art thermoelectric material is large in electric resistivity ρ. The electric resistivity ρ is sensitive to heat, and, for this reason, the users hesitate to use the prior art thermoelectric material in high-temperature ambiences.

This results in that the heat source raises the temperature.

Images