Silver, thallium, copper and tellurium-based thermoelectrical se

Details Silver, thallium, copper and tellurium-based thermoelectrical se Silver, thallium, copper and tellurium-based thermoelectrical se

1988-04-19

1990-05-29

Nelson, Peter A.

Batteries: thermoelectric and photoelectric

Thermoelectric

Having particular thermoelectric composition

136241, 136201, H01L 3520

Patent

active

049292820

DESCRIPTION:

BRIEF SUMMARY
SUMMARY

The invention concerns silver, thallium, copper and tellurium-based thermoelectric semiconductor thermoelectric material, represented by the general formula (I): heating at about 500.degree. C., under vacuum or under inert atmosphere, slow cooling up to room temperature. in order to obtain an ingot, then
The invention concerns a new thermoelectric material with a high figure of merit, which can be used for thermoelectric conversion of energy, especially at room temperature, a preparation process, as well as the thermoelectric converter obtained from such material.
In a thermoelectric converter (or Peltier effect) an electrical current which flows through the junction at the two p type and n type semiconductors, induces a release or an absorption of heat, according to the direction of the current. That effect is used in various cooling, heating and temperature control devices. For instance, in a cooling device these semiconductor pellets are typically aligned electrically in series and thermally in parallel, making a series of p and n junctions that create a cooling effect when electrons flow from the p to the n pellet.
The coefficient of performance (COP) of a heat pump, in other words the ratio of the quantity of heat released at the hot source (or absorbed at the cold source) to electrical energy supplied at the pump, increases with Z, the thermo element figure of merit. That figure of merit Z depends on the thermoelectric power S (or Seebeck coefficient expressed in V/.degree.K), the electrical conductivity .sigma. (.OMEGA..sup.-1 cm.sup.-1) and conductivity X (W/cm..degree.K) of the material, by the relation of the thermal conductivity X:
The product ZT of the figure of merit by T=(T.sub.c.sup.+ F.sub.f)/2, average temperature of the hot and cold functions, expressed in .degree.K., determines the coefficient of performance and the efficiency of the thermoelectric converter. For a temperature T, close to the room temperature, the product ZT of an usual thermoelectric material such as bismuth telluride (Bi.sub.2 Te.sub.3) or alloys that derived from it, is usually less than or at most equal to the unit. Hence, the coefficient of performance of the heat pumps executed with these materials is low.
The figure of merit Z of a specific semiconductor material can be brought to its optimal value Zopt with adequate doping (if we know how to carry that out). The Zopt value of a material can be deduced from the values of the thermoelectric power, and electric and thermal conductivities, measured on a sample of the same material, not ideally doped. We can show for instance, with Simon curves (Adv. Energy Conv. Vol. 1, 81-92, 1961-Ibid, Vol. 3, 515, 1830-J. Appl. Phys., Vol. 33, 1830-41, 1962), that the optimal coefficient ZT of the materials which are currently known cannot exceed significantly the unit in the temperature ranges where they can be used.
It seemed desirable therefore to produce thermoelectric materials with a higher figure of merit, (ZT>1) of which the economic interest is especially significant for executions of static heat pumps which operate close to the room temperature. Various semiconductors have been studied, knowing that we can modify their figure of merit in doping or by stoichiometric deviation, in order to optimize their thermoelectric power and electrical conductivity.
French patent application 2,566,585 describes silver, thallium and tellurium-based thermoelectric semiconductor materials that can display a figure of merit close to 1 at room temperature, which can be used in the manufacturing of Peltier effect heat pumps.
The purpose of this invention is a new class of thermoelectric semiconductor compounds which possess a high figure of merit, that can be used for thermoelectric conversion of energy, especially in the Peltier effect heat pumps, within a temperature range from about -100.degree. C. to +100.degree. C., as well as a process for preparing those materials.
The new thermoelectric semiconductor materials according to the invention can be represented by the general f

REFERENCES:
patent: 3852118 (1974-12-01), Hampl, Jr.
patent: 3853632 (1974-12-01), Hampl, Jr.
patent: 3932291 (1976-01-01), Donohue
patent: 4589918 (1986-05-01), Nishida et al.

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