Sept. 20, 1960
2,953,617
R. R. HEIKES EI‘AL
THERMOELEMJSNTS AND DEVICES EMBODYING THEM
Original Filed April 16, 1957
Fig.l.
sale"?
‘20
2.5 '
.035 -
.03 -
.02'5 .02 '
.Ol5 -
OI
005
.
T24
3O
I80 -
28
I60
I40
26v——%lllh—r( -
IOO -
so -
so
55 x lo-l»
30
25
20'
2.5
.04 ~
.03
'
7.02
.Ol5
.Ol .005 '
I00
260 abo 400 soo e00
Temperature "K
PI’OPGI‘TIBS of Li_°3Mn_97Se
700
860
INVENTORS
Robert R. Heikes 8»
William D. Johnston
BY
United States Patent ‘0
CC
2,953,617:
Patented Sept. 20, 1960:
1
2
where T is the absolute temperature, 1r is the Peltier co
2,953,617
e?icient in calories per coulomb for the thermoelement,
p is the electrical resistivity, K is the thermal conductivity
THERMOELEMENTS AND DEVICES
EMBODYING THEM
for the thermoelement member and a is the Seebeck co~
efficient in volts per ° C.
Robert R. Heikes, Wilkinsburg, and William D. Johnston,
Pittsburgh, Pa., assignors to Westinghouse Electric Cor
poration, East Pittsburgh, Pa., a corporation of Penn
sylvania
Where two thermoelement ‘
members having differing resistances and thermal C0111
ductivities and Peltier coefficients are employed in pairs,
the index of el?ciency of the combination may be com
puted from the following equation:
10
Continuation of application Ser. No. 653,245, Apr. 16,
1957. This application Oct. 3, 1958, Ser. No. 765,026
6 Claims. (Cl. 136-45)
in which p1 and p2 are the electrical resistivity of each
of the thermoelement members, a is the thermoelectric
The present invention relates to thermoelements and 15 power
in volts per ° C., K is in watts per cm./deg. C.,
thermoelectric devices embodying the same.
and p is in ohm centimeters.
This application is a continuation of our application
In some cases, another parameter often employed to
Serial No. v653,245, ?led April 16, 1957.
describe the merit of a thermoelectric material is the
It has been regarded as highly desirable to produce
?gure of merit, Z as de?ned by the following equation:
thermoelectric devices wherein either an electric current 20
is passed therethrough whereby to provide for cooling
applications or alternatively a source of heat is applied
to one junction of the thermoelectric device to bring this
T
junction to a given elevated temperature while the other
where M is the index of efficiency.
junction is kept at a lower temperature, whereby an 25 a For the best presently available thermoelectric ele
electrical voltage is generated in the device. For refrig
ments for power generation the 'maximum index of
eration applications in particular, one junction of the
efficiency is approximately 0.05 to 0.1 (5% to 10%)
thermoelectric device is disposed within an insulated
and for the vast majority of thermoelectric elements
chamber and electrical current is passed through the
it is substantially below 0.05. Commercially accept
junction in such a direction that the junction within the 30 able thermoelectric elements should have an index of
chamber becomes cooler while the other junction of the
efficiency of M equal to at least 0.1 for the tempera
thermoelectric device is disposed externally of the cham
tures to be applied to the junctions, and preferably 0.15
ber and dissipates heat to a suitable heat sink such as the
atmosphere, cooling water or the like.
_ Previously, available materials for thermoelectric de
vices have been experimented with extensively. The best
possible combinations of materials known heretofore have
and higher. While in substantially all ordinary metals
the product of pK is reasonably small, V is of the order
35 of 30 microvolts per ° C. and as a consequence the in
dex of e?iciency is much less than ‘0.1 usually being less
than 001..
This invention is directed to the preparation of mixed
been ine?icient and relatively unsatisfactory for one or
more of the following reasons:
'
valence inorganic compounds having relatively low pKH
(1) The maximum veri?ed temperature drop in the 40 coe?icients and having a thermoelectric power (often,
cold junction of the thermoelement is approximately
called the Seebeck coe?icient) V of the order of 100 to
32.5 ° C.-—such temperature drop is inadequate for most
1000 microvolts per °C. The electrical resistivity of
practical refrigeration apparatus. While in the litera~
this material is of the order of 10*2 ohm centimeters.
ture there have been made claims for temperature drops
The thermal conductivity is of the order of 0.02 watt per'.
of up to 60° C. to 80° ‘C. with individual elements the 45 cm. per degree ‘C.
materials and the structures have not de?ned.
The object of this invention is to provide thermoelec
(2) The efficiency of the thermoelectric device based
tric devices comprising a thermoelement of which at least
on'the electrical energy supplied thereto is quite low, at
best amounting to approximately 1%: of the e?iciency ob-V
tainable with a common compression refrigeration unit.
, The passage of an electrical current througha thermo
electricdevice results in the absorption of heat at one
junction and evolution of heat at the other junction there
of.’ In‘ addition thereto, the passage of an electrical
one member is a homogeneous solid of a mixed valence
transition metal chalcogenide.
5.9I
A further object of the invention is to provide thermo-'
electric devices embodying non-stoichiometric inorganic.
compounds suitable for use in thermoelectric devices‘
having a high index of e?iciency or ?gure of merit. '
Another object of the invention is to provide a thermo
current through the elements produces Joule heat which 55 electric device in which an inorganic compound ‘forms
isv proportional to the second power of the electrical
one element and a metal forms the other element of av
current ?owing therethrough. Any heat generated in the
thermoelement pair.
thermoelements will ?ow toward the cold junction as
well _as toward the hot‘junction of the thermoelectric de
vice,
The electrical resistivity of the thermoelement
members of the device and the thermal conductivity
should be as small as possible.
Thermoelectric devices may be ‘tested and a number
A still further object is rto provide a thermoelectric
device in which one element comprises the sul?de, sele-v
60 nide or telluride of lithium manganese.
I
‘Other objects of the invention will in part be obvious‘
and will in part appear hereinafter. For a better under?"
standing of the nature and objects of this invention, ref-hi
indicating its relative effectiveness, called the “index of
erence should be had to the following detailed description‘;
e?iciency” (which sometimes has been called ?gure of 65 and drawing in which Figure 1 comprises graphs plotting
merit) may be computed from the test data. The higher ~ - temperatures against various properties and ‘Figure 2 is‘
the index of ei?ciency the more e?icient is the thermo
electric device. The index of e?‘iciency M for a thermo
element member may be de?ned as follows:
(1)}
'
'
"70
a schematic view partly in cross section of
a therrn0—_
electric cooling device.
Highly useful thermoelements are single phase mixed:
valence compounds having the formula LimT(1_‘m)X'
‘ where T represents at least one transition metal “from the;
group consisting of manganese, iron, nickel, cobalt, "cop?
"2,953,617
3
.
compound.
.001. When 7X 7 represents oxygen, especially suitable
transition metals are copper and nickel. The homoge
neous solids of this formula may be employed as the
V.
a
4
.
duce the desired lithium substituted transition metal
m has a value not exceeding about 0.1 and not less than
-
.
from 600° C. to 1200° C. for a period of time to pro
consisting of oxygen, sulfur, selenium and tellurium and
positive element of a thermoelement pair.
.
in a sealed container and heated to a temperature of
7 pier and zinc’, ‘X represents a chalcogenide from the group
>
The inorganic compounds LimMn(1_m)Se, LimMn(1_m)S
and LimMn(1_m)Te where’ m has a value of from 0.001
to.O.1l, have proven to have exceptional merit as a thermo
'
electric element. These respective. selenide, sul?de and
telluridecompounds may be prepared by thefollowing
*A suitable negative element to cooperate with the posi
tive element may be composed ofva homogeneous solid ‘
having the formula AlnT(1_n)X, where T represents one 10 reaction :
or more transition metals, X has the value previously
A
7 given and n has a value offrom 0.1 vto 0.001.
speci?c composition of this compound has the formula
AlnCll(1__n__p)ZI1pO
15
wherein n has a value of from 0.1 to 0.001 and p has a
value not exceeding (1—n).
~
_
> Other suitable positive and negative thermoelement
components may comprise compounds having the form
ula MZME) where M represents an element from the 20 where m has the value of from 0.001 to 0.11. ' The upper
group consisting of'chromium, iron, nickel, copper, cobalt
limit value for x is the point where a second phase forms.
In preparing the respective compounds, the several rc
and manganese and Z represents an element selected from ’
thegroup consisting of sulfur, selenium, tellurium, arsenic,
actant matenials are powdered under a protective atmos
phere, such as argon or helium, and admixed in the de;
'sired mol proportions. The mixture is pressed at a pres
antimony and bismuth and has a positive value of less
than 0.1.
'
,
‘When the compound has the formula MZ(l+a>,'homo
sure, for example, of up to 10,000 p.s.i., into pellets.
geneous members thereof may function as the positive
The pellets are supported on a refractory, for example;
a plate of magnesia or graphite, and disposed in an
evacuated chamber of quartz or ceramic, the vacuum be
element. Conversely, when theqinorganic compound has
the formula MZ(1_,,), homogeneous members thereof will
function as the negative element. Thermoelement pairs 30 ing below 0.1 mm. of mercury,and ?red above 500°‘ C.,
but below the decomposition temperature of the com~
'of these groups‘ and joining the terminals-of a positive.
pounds, i.e. not above about 850° C. for the selenides.
to a negative element. Furthermore members of the ' A'suitable ?ring schedule is 550° C. for 12 hours and
compound having the formula MZ(1+a) may be paired
then at 650° C. for 24 hours. This produces a single
'with members of the compound having the formula 35 phase solid material having rock salt crystal structure
AlnTugmX' to form satisfactory thermoelements. Mem
where m does not exceed 0.11 for the selenide.
bers of the compound having the formula MZ(1_,,) may
In preparing the ?red pellets, it has been, discovered
be paired with members of the compound having form
that the magnesia support. will absorb or react with any
'ula LimT(1_m)X to provide satisfactory thermoelements.
second phase Li2Se that may be present as a liquid dur
It will be understood that all of these inorganic com 40 ing the higher ?ring temperatures. Therefore, if there
pounds are homogeneous for the purpose of this invention.
is inadvertently added an excess of the Li2Se above the
It has been discovered that highly satisfactory thermo
amount that forms a single phase product, i.e. beyond
elements may be prepared by combining a metal member . > the value of m=0.ll in the reactant selenide mixture,
with a member of any of the homogeneous inorganic com
the magnesia will effectively remove it from the pellet
45
may be prepared by employing members of from each
‘ pounds, either positive or negative elements.
during ?ring. Consequently magnesia supports are de
Examples
ofrsuitable metals are copper, silver, copper base alloys,
sirable for contact with the pellets.
Ina similar way, the sul?de and telluride analogues.
silver base alloys and molybdenum. Any metal which
is solid under conditions of use and non-reactive with the
of the LimMn(1_m)Se may be prepared. Lithium tellu-'
' inorganic compound or the atmosphere or surrounding
50 ride (LizTe) and lithium sul?de (LiZS) may be ?rst pre
medium can be employed in such thermoelement devices.
pared by a vapor reaction as indicated for the selenide.
' The following. example illustrates the practice of the
Copper will give excellent results when associated with
a member ‘of the compounds MZQH), LimT(1_m)X or
invention.
'
.
'
Example I
Speci?c potentially useful thermoelement members may
be prepared from‘ compounds of chromium or manganese.
55 ' While lithium selenide may be'prepared by several
reacted with tellurium, arsenicgantimony'and bismuth
wherein there is either a slight-excess or deficiency of
methods known in the art, it has been found that they
following method is particularly satisfactory. A quantity
of lithium metal is placed in‘ a stainless steel or magnesia
tellurium, arsenic, antimony" or bismuth over the metal “ boat,
and placed within a large vessel of quartz or Vycor
cation. Examples of compounds of this type are'chromi 60
glass
in
which an excess of selenium was disposed ina
um telluride, manganese arsenide, manganese telluride,
second
boat.
The large vessel was sealed, evacuated to
,' manganese bismuthide and manganese antimonide. In
. all cases the anion preferably does not exceed 0.1 mol
' excess
or
de?ciency.
These nonstoichiornetr-ic 7 com
1 micron pressure, and heated to 300° 'C. whereby sele
nium vapors were freely evolved. After 24 to 48 hours,
all'of the lithium had been converted by the selenium .
pounds are readily prepared by, admixing the manganese 65
vapors into LiZSe. No polyselenides were found. The
or chromium with the desired amount of the anion and
. ?ring the mixture within a protected atmosphere. .The
reaction product may be compressed into a’ pellet and
sintered at elevated temperature to produce a relatively
product is of cream color, and may be either of amor
phous or dendritic physical shape; It is extremely re->
active with air and'must be protected from contact with
the atmosphere.
solid member.
7
. '
-
70 ‘ Manganese selenide may be readily prepared from’
_ The lithium substitutedtransition metal chalcogenides
may be prepared as disclosed in our-copending patent ap
plication Serial No. 580,856, ?led April 26, 1956. Brie?y;
this comprises preparing a transition metal oxide and
then admixing "it intimately with lithium peroxide. The 7
intimate‘ mixture compressed'into a pellet placed with:
powdered electrolytic manganese, or other pure‘mangam
nese, and selenium. The powdered manganese and sele+
nium are admixed in equimolor proportions; and pressed
into pellets. The pellets are placed in a sealed tube and
5 ?red. A suitable ?ring‘schedule is 2 hours at 200° (2.,
2,953,617‘
6
2"ho'urs at 300° C. and '12 hours at 550° 0. and ‘24
hours at 650° C.
crushedqto a ?ne powder and sufficient zinc oxide added’
thereto to provide :1, to 10 mol percent of zinc oxide‘ and
from 0.1 to 10 mol percent of the aluminum, and not
less than 80 mol percent of copper. This mixture of
The manganese selenide pellets are crushed in a pro
tective atmosphere to a ?ne powder, the desired amount
of powdered lithium selenide and selenium is added there
to and the three components admixed. The mixture is
handled in a dry box ?lled with argon, for example, and
oxides is then melted and solidi?ed to form a solid homo
geneous member. -
’ Referring to the ?gure of the drawing, there is illus
trated a thermoelectric device suitable for ,e?lecting re
pelleted at 10,000 p.s.i. into pellets of 0.5 inch diameter.
The pellets are placed on a magnesia plate disposed with
frigeration. A thermally insulating wall 10 so formed‘
in a vessel of Vycor glass which can be sealed, and 10 as to'provide a suitable chamber, is perforated to permit
?lled with argon,‘ for‘example. The pellets are heated
passage therethrough of a positive thermoelement mem
for. 12 hours at 550°' C. and then for 24 hours at 650°
ber l2 and a negative thermoelement member 14. An
C., which results "in'a' product having the formula
LimMn(1;,,,,se. ‘These ?red pellets are stable in air. By
this procedure ‘several pellets were prepared wherein
lithiumjcompri's'ed002,0.05, 0.08 and 0.1 mole the re
specftive'. ‘formulae being ' Li_0"2Mn;9ase; Li0_05Mn_95Se;
electrically conducting strip‘ '16 of metal, for example, is
joined to an" end face 18‘ of the member 12 and end face‘
15
20'of the'member 14 within‘ 'the chamber so as 'tofproi‘
vide‘ good electrical and thermal contact therewith. 7 The
end, faces 18 and ,20 may be coated with a thin layer'v
of 'rnetal,,for example, by vacuum evaporation or by use
The attached Figure 1 was derived from tests made on
of ultrasonic brazing,,_whereby good electrical contact
a ?red pellet prepared as ‘in Example ‘I. of the compound 20 angle-thermal adherence thereto is obtained. The metal
Li_0,M1i~_;,',se. ‘The-thermal conductivity, electrical re
strip-16 of eoppensilver or the like may be brazed or
Li5_'o8Mn_9§Se'and LijMnQSe'.
"‘
sistivity and Seebeck coel?cient were evaluated ‘at tem
solderedi'to/the metalcoated' end faces 18 and 20. The
peratures of up to 825° C., and the curves A, B, and C
metal strip '16 may be provided with suitable ?ns or other
were plotted from data obtained in tests. Tabulations
means for conducting heat thereto from the chamber in
from these test values were then employed for deter 25 which it is disposed. At the end of the member 12 lo
mining the index of e?’iciency and ?gure of merit of this
cated on the other side of wall 10 is attached a metal
compound and plotted as curves D and E in Figures 1.
plate or strip 22 by brazing or soldering in the same man
Extra polation of curve D indicates that the index of
ner as was employed in attaching strip 16 to end face
e?’iciency at 1000° C. will attain a value of 15%.
18. Similarly a metal strip or plate 24 may be con
Suitable negative members for a thermoelement pair 30 nected to the other end of member 14. The plates 22
to associate with the LimMn(1_m)Se, as well as the cor
and 24 may be provided with heat dissipating ?ns or
responding sul?des and tellurides, are stoichiometric com
other cooling means whereby heat generated thereat may
pounds of groups III and V of the periodic table—for
be dissipated. An electrical conductor 26 attached to a
example, indium arsenide.
source 28 of direct current is ai?xed to the end plates
35
A positive thermoelement member may be prepared
22 and 24, A switch 30 is interposed in the conductor
by admixing ?nely divided copper oxide and zinc oxide
26 to enable the electrical circuit to be opened and closed
in proportions providing 0.92 mol of zinc oxide and 0.07
as desired. When the switch 30 is moved to closed
mol of copper oxide, and 0.01 mol of lithium peroxide
position, electrical current from the source 28 ?ows
is added 0t this mixture. A pellet formed by compress
through the thermoelements 12 and 14 whereby cooling
ing the mixture is placed within a sealed container of 40 is e?ected within the metal strip 16 and heat is generated
at plates 22 and 24.
platinum and then hetated at an elevated temperature of,
for example, 900° C. for a period of several hours until
It will be appreciated that a plurality of pairs of the
a homogeneous reaction product is produced. The reac
positive and negative members may be joined in series
tion product is in the form of a sintered pellet, which is
in order to produce a plurality of cooperating thermo
inhomogeneous in density and has a relatively high in 45 elements. The cold junctions of each of these joined
ternal resistance and consequently is not suitable for the
thermoelements will be placed within a suitable cham
purpose of producing satisfactory thermoelectric devices.
ber to be cooled while the hot junctions will be so dis
posed that they will reject heat to a suitable heat sink.
This sintered pellet, therefore, is fused at an elevated
temperature and recrystallized into a solid homogeneous
In a similar manner the thermoelements of the present
body, preferably a single crystal, by withdrawing it at 50 invention may be disposed with one junction in a furnace
or other source of heat while the other junction is cooled
a slow rate from the furnace whereby during cooling
by applying Water or blowing air thereon or the like.
controlled solidi?cation results. Single crystals will have
Due to the relative difference in the temperature of the
a resistivity of the order of 0.01 ohm-cm. The thermal
junctions, an electrical voltage will be generated in the
conductivity of the sintered pellet is not signi?cantly
di?'erent from the thermal conductivity of the single crys 55 thermoelements. By joining a plurality of the thermo—
tal or other solid homogeneous body. Consequently, the
elements, direct current at any suitable voltage will be
generated.
formation of a recrystallized or single crystal body re
It will be appreciated that the above description and
sults in a marked reduction of the factor pK. The re
drawing are only exemplary and not exhaustive of the
sulting single crystal may be cut to produce a suitably
shaped positive thermoelement member.
60 invention.
We claim as our invention:
For a negative thermoelement member an alloy is pre
1. A thermoelement device comprising one member of
pared from aluminum and copper in an amount equal
a homogeneous solid having the formula LimT(1_m)X
to less than 10 atom percent of the aluminum. The alloy
where T represents at least one transition metal from the
may be in the form of thin sheets, powder, wire or the
like. The alloy is then heated in an oxidizing atmos 65 group consisting of manganese, iron, nickel, cobalt, cop
per and zinc, X represents a chalcogenide from the group
phere under conditions wherein oxidation proceeds very
consisting of oxygen, sulfur, selenium and tellurium, and
slowly. To this end the atmosphere may comprise a
in has a value not exceeding about 0.1 and not less than
very low partial pressure of oxygen of the order of one
micron or less, and the temperatures should be relatively 70 0.001, and another member comprising a negative thermo
element material electrically connected to one portion
low, for example, below 500° C.‘ ‘After several hours
of the said one member.
of oxidation under these conditions the oxygen partial
2. A thermoelement device comprising one-member
pressure may be increased and the temperature raised
of a homogeneous solid having the formula LiMn(1_m)X
whereby the entire aluminum-copper alloy is rapidly com
where X represents a chalcogenide from the group con
pletely oxidized. Thereafter the resulting mixed oxide is 75 sisting of oxygen, sulfur, selenium and tellurium, and m
2,953,617
7
7
V
hasfa valuenot‘ exceeding about 0.11 and'not less than,
0.001, and another memberelectrically connected to, one
portionof the‘ said one member,_ said another member
composed of a homogeneous solid comprising a stoichi
ometriccompound'of at least one element of group 'III
selected from the group consisting of indium, aluminum
and' gallium, and at least one element from group V
selected from the group consisting of antimony, phosphor
us. and arsenic.
'
I
,
-
'
_
8
, 6.1A thermoelement device comprising one memberrof‘
homogeneous solid lithium manganese telluride having;
from about 0.1 to 0.001 mol of lithium, and the-other"
member comprises, a ‘negative thermoelement material, electrically connected to. one portion of the said ‘one . '
member.
7References Cited in the ‘?le of this patent
UNITED STATES PATENTS
'
IS. The thermoelement device of'claim 2 wherein the 10v
said another’ member comprises indium arsenide.
'
286,288
685,471
Frasch .._._'_ _______ __,____ Oct. 9, 1883
Hermite et‘al. __; ______ __ Oct. 29, 1901
.4. A thermoelement device comprising one member of
775,188
homogeneous solid lithium manganese sul?de having from ‘
2,232,960
about-0.1 to v0.001 mol of lithium, and therother mem
2,397,756
bergcomprises a negative theremoelement material elec 15' 2,602,095
. Milner __________ _;..._._.. Feb.‘ 25, 1941
Schwartz ____ ..;_ _____ .._ 'Apr. 2,‘ 1946
Faus _______'_...._' _______ __. July 1, 1952
2,685,608
Justi' ____________ __'____._ Aug.‘3, 1954
2,798,989
Welker __..;.'.___'__' _____ __ July 9, 1957
' trically, connected to ‘one portion ,ofthe said ‘one mem- .
ber.
.135. VA thermoelement
" g ,'
, device comprising one member
of_ ‘homogeneous solid lithium manganese selenidehaving
from about 0.1 tov 0.001 mol of lithium, and the other; 20.
member-- “comprises a negative thermoelement material
electrically connected, tovione portion ,of the said one
member.
'
'
'
1
-'
~
Lyons et a1 ________ _.._..__ Nov. 15, 1904
OTHER'REFERENCES >
Journal of Applied Physics, vol. 18, No. 6, December"
1947, pp. 1124-5‘.