DE1170024B - Thermoelectric material - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

EDITORIAL

Boarding school Kl .: HOIm

Number: File number: Registration date: Display day:

German class: 21b - 27/03

W 31846 VIII c / 21b

March 14, 1962

May 14, 1964

The invention relates to a new, improved thermoelectric material with the crystal structure of thorium phosphide (Th ₃ P ₄ ) and to components produced therewith.

When evaluating a thermoelectric material, the experts have a compound Marks created with the name Effectiveness (Z). The effectiveness can be derived from values that are at Experiments obtained with the thermoelectric material can be calculated. The higher the Effectiveness Z, the more effective the material is. The effectiveness Z for a thermoelectric material is defined as follows:

It is
α the Seebeck coefficient (V / ⁰ C),

ρ is the specific electrical resistance (ohm cm),

K is the thermal conductivity (watt / cm ⁰ C).

From the above equation it can be seen that the effectiveness of a thermoelectric material is increased if the specific electrical resistance ρ is considerably reduced if the Seebeck coefficient or the thermal conductivity K do not change accordingly at the same time. The invention is directed to a method of obtaining this result in a thermoelectric material which has a high percentage of vacancies and which is semiconducting in some areas of its composition, but whose carriers have low mobility, such as thermoelectrics which have a thorium phosphide lattice (Th ₃ P ₄ ) own.

The invention relates to a thermoelectric material with a thorium phosphide structure. According to the Invention, the number of vacancies in the lattice is reduced by neutral doping, so that an increase the carrier mobility in the material without significantly changing the number of charge carriers is reached. The material for neutral doping can be monovalent or divalent from chalcogenides Metals exist. The thermoelectric material can consist of at least one element of lanthanum or Rare earth actinium series, composed of at least one element of the sulfur group, selenium or tellurium and consist of neutral dopant. The thermoelectric material can do a lot Thermoelectric material

Applicant:

Westinghouse Electric Corporation,

East Pittsburgh, Pa. (V. St. A.)

Representative:

Dr. jur. G. Hoepffner, lawyer,
Erlangen, Werner-von-Siemens-Str. 50

Named as inventor:
Forrest L. Carter, Monroeville, Pa.,
Robert C. Miller, Pittsburgh, Pa.,
Robert R. Heikes, Export, Pa. (V. St. A.)

Claimed priority:

V. St. v. America March 24, 1961 (98 020) - -

Doping material in the amount between 0.001 and (ix - - ■> -) can be added, where χ can run between 1.33 and a maximum at 1.5 if the metal of the halide is monovalent; however, an amount of doping material in the amount between 0.001 and (3 χ -4) can also be added to it, with χ being able to run between 1.33 and 1.5 if the metal of the chalcogenide is divalent. The thermoelectric material can according to the formula

■ A Af (O ₁ OOl to 2 y) Z _x 5 (0.001 to y)

be composed, where A at least one element of the lanthanum or actinium series of the rare earth elements, M, at least one of the monovalent metals lithium, sodium, potassium, copper, silver or gold, Z at least one element of the chalcogens sulfur, selenium or tellurium, B is at least one element of the chalcogens sulfur, selenium or tellurium and χ can run from 1.33 to a maximum of 1.5 and y according to the formula

3 4

is determined. The thermoelectric material can, however, also according to the formula

A Λ ^ ο, οοΐ to y) 2 ^ .8 (

to y) 2 ^ .8 (0.001 to y)

be composed, where A is at least one element

409 589/118

the lanthanum or actinium series of the rare earth elements, JV "at least one of the divalent metals barium, strontium, magnesium, indium, cadmium or zinc, Z at least one element of the chalogens sulfur, selenium or tellurium, B at least one element of the chalcogens sulfur, Selenium or tellurium and χ can run from 1.33 to a maximum of 1.5 and y according to the formula

y = 3.V - 4 ₁₀ '

is determined.

The thermoelectric material can according to the formula

Material, in particular one with a Th ₃ P ₄ structure; The number of vacancies in the atomic lattice structure is reduced by neutral doping, the mobility of the charge carriers increasing without essentially changing the number of charge carriers in the material.

According to a further object of the present invention, a thermoelectric material is provided with the general formula

and

AM ₂₁₁ Z _x By

ANyZ _x By

Q, ₀₀₁ to

15th

be composed, where χ can run from 1.33 to 1.5 and y from the formula

1 + y ₌ 3

~ ^x + y ^4th

is determined. The thermoelectric material can also according to the formula

CeS _{1) 39} (SrS) o _iO71

be composed. The thermoelectric material can also according to the formula

CeS ₁ 3g (SrS) ₀ , u

be composed. The thermoelectric material can also according to the formula

CeS ₁₄₂ (SrS) _{0, 09}

be composed. The thermoelectric material can also be according to the formula

25th

), 18

be composed.

In the description of the invention, the term "lanthanides" means combinations (alloys) the lanthanum series of rare earth elements. The lanthanum series includes lanthanum, cerium, Praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, Erbium, Thulium, Ytterbium, Lutezium (Cassiopeium).

The term "actinides" means combinations of the actinium series of the elements of the rare ones Earth. The actinium series includes thorium, pratactinium. Uranium, Neptunium, Plutonium, Americium, Curium, Berkelium, Californium, Einsteinium, Fermium and mendelevium. The last new elements are highly radioactive and are only used under certain conditions Precautions used.

Neutral doping is the addition of an element or composition (alloy) to one thermoelectric material to reduce the number of voids in the crystal lattice structure, without changing the number of load carriers.

Monovalent chalcogenides, as they are useful according to the teachings of this invention, are oxides, sulfides, Selenides and tellurides of monovalent metals.

Divalent chalcogenides according to the teachings of this invention are oxides, sulfides, selenides and tellurides divalent metals.

When the chalcogenide is a metal oxide, there is a possibility of phase transformation in some cases of the thermoelectric material.

The present invention relates to a method for improving the effectiveness of a thermoelectric created.
It is

A at least one element of the rare earths from the groups of the lanthanum and actinium series, M at least one monovalent metal, N at least one divalent metal, Z at least one element of the chalcogens

Sulfur, selenium and tellurium, B at least one element of the chalcogens sulfur, selenium and tellurium,

.v changes from 1.33 to a maximum 1.5, and

y varies from 0.001 up to a value y _ma x, where ymax χ in the first formula ₅ - and .v in the second formula 3 - is the fourth

The teachings of the invention are particularly directed to the manufacture and doping of thermoelectrics Materials made from sulfides, selenides, tellurides and phosphides of the lanthanum and actinium series of Rare earth elements applicable.

Substances that can be used for neutral doping are monovalent or divalent metal chalcogenides. These include BaS, SrS, PbS, SnS, MgS, CaS, ZnS, CdS, Ag ₂ S, Cu ₂ S, K ₂ S, NaS and LiS. However, this is not an exhaustive list. The corresponding selenides and tellurides of the metals can also be used.

In particular, the specific resistance ρ of a thermoelectric material is a function of the electron concentration «, a constant, the electron charge e, and the electron mobility μ. The relationship between them is:

_ 1

^ρ ~ en-μ '

From this relationship it can easily be seen that if one or more of the values η or μ increases without affecting the others in the opposite direction, the relative resistance will decrease.

Where e is a constant. It has now been found that by neutral doping of sulfides, selenides and tellurides of the rare earth elements of the lanthanum and actinium series with monovalent and divalent chalcogenides, it is possible to increase the electron mobility μ of the substance without the electron concentration η in the opposite direction to influence. This lowers the specific electrical resistance ρ of the substance. The neutral doping increases the electron mobility μ by reducing the number of vacancies in the lattice structure of the substance.

In addition to the considerable reduction in the value of the electrical resistivity ρ

The thermoelectric material can make other improvements to the thermoelectric material Material can be expected as a result of the neutral doping.

The elimination of the vacancies in the grid reduces the free energy because of local stresses provided, of course, that the charge balance is not disordered and that the vacancies are not filled by atoms that have a larger ionic radius than those that can be easily accommodated. Under these conditions the neutrally doped thermoelectric Material be more stable in a wider temperature range than non-doped material.

The elimination of vacancies in the atomic lattice by neutral doping also results in a reduction in size the diffusion rate in the material doped in this way, both for anions and cations as well as for neutral gases and other contaminants. Therefore, the lifespan should also be more thermoelectric Materials treated with neutral doping grow.

The elimination of the voids also results in an increase in the number of useful thermoelectric materials. a ₅

In certain other cases, the neutral doping can reduce the thermoelectric properties of Improve thermoelectric materials in that the grid of the substance is contracted or is widened; in some cases, e.g. B. when cerselenide is doped with magnesium sulfide, can reduce the lattice thermal conductivity of the fabric.

The neutral doped thermoelectric materials made according to the teachings of this invention have one of two general formulas, depending on whether the substance is a neutral doping agent Chalcogenide of a monovalent or divalent metal is. When a chalcogenide of a monovalent metal is used, the general formula can be as follows be given:

■ AM ( _iVmax ) Z _x B (y _max ).

When a divalent metal chalcogenide is used, the general formula can be as follows be written to:

From the general formulas described above it can be seen that y represents the amount of neutral dopant used. This can be explained well if one considers the chemical reaction for the production of cerium sulfide, which is neutrally doped with divalent strontium sulfide.

+ y

When calculating the value of y to determine the amount of divalent neutral dopant, the above formula gives the equation

1 +

X + ymax

3 4 '

where -: - the ratio of the cations to the anions

is when all places in the grid of the undoped material CeS _{2 are} filled. For two-valued neutral doping then y _ma x = 3x - 4; in doing so, χ changes from 1.33 to a maximum of 1.5. In the same way, y _max , ie the maximum amount of the dopant used, can be determined by the formula

4 5

AN (y _max ) Z _x B ( _Smax ) .

It is

A at least one element of the lanthanum or actinium series of the rare earths; these series were defined above,

M at least one monovalent metal from the group silver, sodium, potassium, lithium, copper or gold,

JV at least one bivalent metal from the group lead, tin, magnesium, barium, strontium, Cadmium, zinc, calcium or bivalent copper,

Z at least one element of the chalcogens sulfur, selenium or tellurium,

B at least one element of the chalcogens

Sulfur, selenium or tellurium, χ runs from 1.33 to a maximum

1.5 and
y is at least 0.001 and can be determined using the method described below.

when a monovalent neutral dopant is used.

In many cases, the best or optimal thermoelectric properties are obtained when less than the maximum amount of dopant is used in the doping of thermoelectric material. Good results have been obtained when CeS ₁₁₃₃ Ms _li5 with an amount of strontium sulfide in one amount

was endowed by about - ^ y max. The specified substance has a thorium phosphide lattice. Good results have been obtained when the amount of doping material was varied from 0.001 mol up to the maximum value given above.

The following examples illustrate the teachings of this invention.

example 1

A quantity of 11 g CeS _li39 and 0.786 g SrS are mixed in a dry argon atmosphere. After mixing, the substance is pressed into a pill about 25 mm in diameter with a total force of about 6800 kp. The pill is then placed in a graphite crucible and sintered in an argon atmosphere for 15 minutes at 1350 ° C.

After sintering, the pill is allowed to cool to room temperature; it is then placed in an argon atmosphere grind so that all of the material passes through a 150-mesh sieve (US standard sieve) passes through.

The finely ground material then becomes a pill approximately 31 9 χ 9 mm for a total force of about 6800 kp pressed in an argon atmosphere.

The newly formed pill is then placed in a molybdenum vessel, the vessel is filled with argon and

6g melted. The vessel is slowly heated to a temperature between 1400 and 1425 ° C and maintain the temperature for about 15 minutes. The jar will then slowly open in an hour

900 ⁰ C cooled, then allowed to cool down to room temperature.

The compact is then removed from the jar and placed in cylindrical pills about 8 mm in diameter and cut about 25 mm in length.

Each pill has a composition according to the formula

CeS _{1> 3e} (SrS) _{0) U.}

The material has a thorium phosphide lattice (Th ₃ P ₄ ).

Example 2

The procedure of Example 1 is _{repeated with 11 g CeS Ii39} and 0.507 g SrS.

The pills produced with this have a composition according to the formula

CeS _lj39 (SrS) _0j07 i.

20th

Without affecting the invention, undoped CeS _{li39 can be} produced.

The specific resistance ρ and the Seebeck coefficient λ of the three materials are at 300 ° K measured; the values are listed in the table below.

Table 1

_30th

35

From the above values is the strong reduction in the specific electrical resistance ρ, which is caused by the neutral doping is caused, can easily be seen. The slight decrease in the Seebeck coefficient, which also results from the neutral doping is insignificant with regard to the strong reduction of the specific electrical resistance.

EXAMPLE 4

The methods of Examples 1 and 2 are followed by similar ones, but in which the sintering in one Graphite crucible was made instead of in a molybdenum vessel. The result is pills with a composition

CeS _1>42; CeS _lf "(SrS) _o , _oe or CeS _lfU (SrS) _OflB .

The specific resistance ρ and the Seebeck coefficient λ of these substances are determined at 350 ^° K and are summarized in the following table.

example material More specific
electrical
resistance
(q) Seebeck
coefficient 1
2
3 CeSi. ₃₈ (SrS) _{0, 071} 38-10-1
l, 8-10-i
0.78-10-i -50
-50
-50

Table 2

material More specific
electrical
resistance
(e) Seebeck
coefficient
(«) CeS _{1> 42}
^ ^e ^ ^> i.42 (SrS) _{0) 09}
CeS _{1> 42} (SrS) _0il8 25.5 · IO- ³
5.1 · IO- ³
5.7 · IO- ³ -34
-36
-40

60

65 These values clearly show how great the reduction in the specific resistance ρ is due to neutral doping. In addition to the reduction in the specific resistance, the material produced with neutral doping shows a slight increase in the Seebeck coefficient, which, however, does not make any significant contribution to the increase in the effectiveness Z of the material.

Just as convincing results as those reported by Tables 1 and 2 can be achieved by the neutral doping of sulfides, selenides and tellurides of each element of the lanthanum and actinium series of the rare earths, which form the thorium phosphide crystal structure (Th ₃ P ₄ ) have, by substituting equimolar proportions in the examples for cerium sulfide.

Furthermore, satisfactory results can be achieved by the neutral doping of sulfides, selenides and / or tellurides of mixed rare earth elements, with thorium phosphide structure, such as. B. Cerium Samarium Sulphides. In Example 1, 11.5 g of Ce _0/5 Sm _0i5 S _{1> 39 can be used} instead of 11 g of CeS _{1> 39} . Corresponding results are obtained.

Thermoelectric materials made according to the teachings of this invention can be used as Legs are used in thermoelectric components and devices, for example in thermal generators, that work according to the Seebeck effect, and in cooling devices that work according to the Peltier effect work. The materials made according to the teachings of this invention can be used to make pills pressed and reduced. They are then provided with metallic contacts, with other thermocouple legs connected with the reverse conductivity and thus result in thermoelectric components.

The materials according to the invention are particularly useful in thermoelectric devices for high temperatures, especially those above 550 ^° C.

From the description and the examples it can be seen that the objects of this invention make it come true.

Claims (11)

Patent claims: 1. Thermoelectric material with thorium phosphide structure, marked thereby e t that the number of vacancies in the lattice is reduced by neutral doping, such that one Increase of the carrier mobility in the material without a significant change in the number of charge carriers is reached. 2. Thermoelectric material according to claim 1, characterized in that the material for neutral doping consists of chalcogenides of monovalent or divalent metals. 3. Thermoelectric material according to claim 1, characterized in that it consists of at least one element of the lanthanum or actinium series of the rare earths, made of at least an element of the chalcogens sulfur, selenium or tellurium and a neutral dopant consists. 4. Thermoelectric material according to one of claims 1 to 3, characterized in that that it has a lot of doping material in amount / 3 4 \
between 0.001 and \ -fx ~ -j is added, where χ can run between 1.33 and a maximum at 1.5 if the metal of the chalcogenide is monovalent, and that an amount of doping material in the amount between 0.001 and Qx-A) is added, with χ between 1.33 and 1.5 can run if the metal of the chalcogenide is divalent. 5. Thermoelectric material according to one of the preceding claims, characterized in that that he is according to the formula ■ "■ M (0.001 to 2! /) * ^ X " (0.001 to y) 15th is composed, where A at least one element of the lanthanum or actinium series of the rare earth elements, M at least one of the monovalent metals lithium, sodium, potassium, copper, silver or gold, Z at least one of the ao elements sulfur, selenium or tellurium, B at least one of the elements sulfur, selenium or tellurium is. 6. Thermoelectric material according to one of claims 1 to 4, characterized in that he according to the formula as A - ^ (ο, οοι to y) Ζχ -ßfo.ooi to y) is composed, where A at least one element of the lanthanum or actinium series of the rare earth elements, N at least one of the divalent metals barium, strontium, magnesium, indium, cadmium or zinc, Z at least one of the elements sulfur, selenium or tellurium, B at least is one of the elements from the group consisting of sulfur, selenium or tellurium. 7. Thermoelectric material according to claim 6, characterized in that it according to the formula is composed, where χ can run from 1.33 to 1.5 and y from the formula l + y ₌ 3
x HY 4 is determined. 8. Thermoelectric material according to claim ?, characterized in that it according to the formula CeS _ll39 (SrS) _{0 <071} is composed. 9. Thermoelectric material according to claim 7, characterized in that it according to the formula CeS _lj39 (SrS) _0ill is composed. 10. Thermoelectric material according to claim 7, characterized in that it according to the formula CeS _lf42 (SrS) _{0, 09} is composed. 11. Thermoelectric material according to claim ?, characterized in that it according to the formula CeS ₁₁₄₂ (SrS) ₀₁₁₈ is composed. 409 589/118 5.64 © Bundesdruckerei Berlin