DE1533328C - Alloy consisting of GeTe and AgSbTe deep 2 - Google Patents

Description

35 to illustrate the present invention. In each

The present invention relates to a trap where special care was taken to

GeTe and AgSbTe., Existing alloy. that only recognized and established assessment

A limited number of compositions drive and standards have been applied and that all

or alloys that were examined by the formula samples by the same method.

CAgSbTe) + CGeTe) ⁴ ° ^ ^{'e mer} g ^to g ^{e e} t> ^enes values were in Allen cases

^{2 l} ~ ^x by determining the mean value from at least

can be expressed are already known and four samples and in the cases; : in which GeTe with

were for use as. Thermocouples in a proportion of 80 to 85 ⁰ Zo of the alloy

proposed thermoelectric devices. In was to kick out by determining the mean value

of the formula, χ is equal to the parts with a molar fraction. 45 12 or 38 samples determined. The schematic diagram

As far as is known, however, none of this alloying was a thermoelectric device and the

wrestling applied in commercial facilities. comparative assessment of the invention in terms of

In technical reports one maintains the commercial on known facilities is in the drawings

Failure to apply to the fact that they contain. It shows.. .. ·

known alloys of the type described above 5 ° Fig. 1 the schematic representation (sectional view

in their thermoelectric performance and sees) 'a thermoelectric device for converting

their mechanical properties reflect the well-known conversion of thermal energy into electrical energy

Lead telluride thermocouples; the-about the same by using the Seebeck effect,

Temperature range are used, not over- F i g. Figure 2 shows a graph of a comparison put or are even inferior. '' 55 of the Seebeck coefficient (α) for the closest related thermoelectric Transducers have been used in the last known alloys and the alloys produced according to these years on the occasion of numerous applications in tempera earth and caused a stir in space. As for doors above the normal temperature gradient for Consequences of this are government agencies and the industrial and electrical facilities and under use substantial funds for research and development of the alloys of the invention for thermal winding purposes expended with the aim of creating suitable elements,

Neten substitute for the lead telluride thermocouples in FIG. 3 is a graphic representation analogous to FIG find, and in the opening, new elements with better- Fig. 2, but based on the specific resistance thermoelectric and mechanical property (/>),

and for the same temperature range to 65 Fig. 4 a graphical representation analogous to

discover. Despite these intensive efforts on Fig. 2, but based on the thermal conductivity

lead tellurid (K) remains in the field of thermoelectrics,

the substance that has the best electrical properties F i g. 5 is a graphic representation analogous to FIG

Fig. 2, which relates to the efficiency ZT . ' Where X = ⁰ K and, y. ■. ■■ '■■. ■,, ·. ·. i. ..- _:

K is equal to the thermal conductivity in watts / ° K cm, F i g. 6 is a graph of the efficiency · (E) of the energy conversion of thermoelectric devices using an alloy according to the present invention or - _; conventional lead telluride alloys; with sodium as the / p conductor. In all cases, commercially available lead telluride with lead iodide was used as the η conductor; In each case, the calculations were carried out according to the known formula for the degree of efficiency, namely

- 'E ■ == ■■

In the above formula, is

Temperature on the hot side, 7 * _t , === temperature on the cold side and / ZT = mit.tleier: efficiency of the tested thermocouple, determined from the entire ^ temperature range. . The ZT values given in FIG. 5 for. 100%> GeTe are known and based on the current state of the. Technology _: well founded. She. were .the book »Thermoelectricity; Science and Technology «by RR Heikes and; RW-Ure, Jr. (P. 435)> taken from 1961 by Interscience Publishers. ν? ·., -,., ':.:., ·. · ..-. ·. "· ...: .. ··; Λ · ...-.->

To supplement the graphical representation in Fig. 2. to, 5 data given is shown in Table I the Characteristic values from the above figures on the basis of this

Λ5 a Temperaturvon'750 ° .K ^ Table I also contains information on the thermoelectric properties of _t hypothetical substances, stöch.ipmetrischer composition, while not in -. Were added to 5 2, Fig ,, but with nevertheless Characteristic curves of the

so graphs shown there consistent

. ■ '■. .: ■ ·. /:■..·.·.- ^: "Table I-. '; · ■■ ' ^: - ^; ' · ■: ■ '■■ <■' ■■■ . Thermoelectric properties at. 750 ° K '.

, ".;'%' GeJe-, .. \ ' _f v : ', _iS ^ AgSbTe _2. ".,; . : «(Μψ ° Κ). ' e (m £ 2, cin). '. ₄ Ki; rnW / crri-? K) _i: '_; · - · .- ■>-Ό; 39 ^; " '50 -' '- ; ~ ^r 228 '^; ■■■ "·" - ■■ · - ^: - \ '4i00' - ^ ■ - ■ =; · ■> ·! 24.3- '■ ·> · ■ ·. - ■ · ■ 0.85 ' - ■■ · : '- "- 7S-- · - ; ■■■ · - ^; Q5 - '" ^: ■: ■" ■■ - --204- - ^:: • 1.72- - ' ^: "2i;5'' ^y - "■ · ■ - ■ 1.52 ^ ■■ · ■ ·· ■: 'SO ' ■■■■■■ '· <·· ' =' ^: 20 ^; : · ■■■■■ · ': - ■ ■ ^219:; V-.1J76 · ■■■ · ': ^; : - ■ - ■■ 13.4 - ·· ' ■ - <"-r; 04 --- ·· • - · ■■: .83 * "· ^; ■■ =" ·· ■ ■ * .i.-.-.: $ - j ·· ; ■■>. ·: * 197 ' ■■ - Ij57 - ^5. · .- -; ., ^: ; / i7.7 ^; ,; / ■■: ·; .- .: '■ ··: «■> :: ■, ··: -'^; i • ■■■ - --83Va ''" ^: - • ii ^ i- ·· i6ä / _s ·:. ·; - <: ■>'- 184 -. . - ^ y 1.35 "· ■" · ■ ' • ^ · · ί; 43 2 '- ^f · - * , - ■ · 85 ·. «Κ ι * -. -Γ _ilSf , _y; .r !, 198 · ■ · ■■ · 'T- ·· - ^:: -t; i9 '^; - ^; · ■■ 1.16 ■■ · ■■ - "855 / 7Λ ·· '■ ■ - ■: -; -M ^ '^; i.-. _: 194 .'X ^ 1.12 21.9 ,,,. ,,, _:! . _ij25 ^ ' -.:■:■; 87 * ^: ■ '■■■■■ ^? -167 ' ^: '0.87 ■ ·' ■ ' ^: ■; · - 20, Ό ^; · '- ■ ■ '?,' ■■■■■ :, :: ■■■ .-. ^ ■ · ■ - ■ ^: '87V ₂ ■■ ·· ^! v- ^ 12V ₂ o; = ■: 168 ■■■ · ' 0.95 ^: - ' ■ i; '/ - ^: "'" -, 'V ■ ··; ·. ·'■;■;' -; v. ■.>: ,, i; 24 ■ · ■■■ '- ■■ '■■■■ ■ 90 = ^v: - ^ .-.! - ο · - ';, ·; - ·: '■' 177 "· ■ - · - '0.82'>'- ^r "· -rs..iv: -23 ·;?) · -ν - :. · '* · * non-stoichiometric composition. ,; ..,.

Since the above-mentioned related alloys are not available, in order to: make a comparison of the alloys according to the invention with the alloys already known; all samples had to be made .; At first; attempted to manufacture thermocouples by cold processing and subsequent sintering. It was found, however, that this method produced completely unsatisfactory results with regard to the mechanical consistency, that is, the samples cracked and crumbled when pressed; B. a series of pegs made of finely divided particles of (AgSbTe ^;, ^ (GeTe) _{0 85} - and in a size conventionally used for cold pressing and sintering, first pressed at a series of pressures between 4000 and 9000 kp / cm and then pressed for * the duration of 4 hours in an atmosphere! ^{sintered at 1} 582; 604 or 627 ° G. The sintered Mäieriül showed in each case the above-mentioned defects That "this problem," ihsbesohdefe in the case of the new alloys composed according to the present invention, can be solved by using a casting process. For this purpose, the alloys were prepared in such a way that the four elements to be alloyed are placed in a Vycor tube in the correct quantities required .! 'would the ^f Dahn evacuated and ^1' was zuges'chmbizen the tube was 'would be heated at 750 °' C then heated 4n-a Rüttelofen ;, ie up; in: forming a melt: the tubes made MAN slowly to about .600 ° O a Cool - and held - at this temperature for the: duration of 16 hours. Then - let the tubes cool down to room temperature. "-

So · Additionally ^; a part of this ^r - casting material was further treated, and - indeed 'by' comminuting into -fine 'particles,' such as' e.g. B. by counting and Siebert with screen size '- * - 35, cold pressing "at 4p00kp / cm-" and subsequent hot pressing'

'55 525 ° e and '35 okp / cm ² for the ^r duration; from'; about 3.0 minutes to make a p-conductor type thermal element. Essentially, the cast samples had the same thermoelectric properties as the samples that were further treated. ^; '' V.

'The thermoelectric substances that are subject to the present invention are ',; were called "alloys" "denotes" because they provide solutions in solid Represent the state of aggregation, no indications of a chemical bond can be determined, and because

65. stoichiometric, compositions of. not stoichiometric seem to differ only by the concentration of the constituents. Basically the microanalysis shows a grid of

Ag —Sb-Ge —Te with a little, over the whole Sample distributed AgTe portion. For samples with a higher germanium content, a lower Ge phase to be available.

One would have to assume that such alloys, in addition to the formation of an actual melt, would not be feasible, because otherwise one would create a suspension of the higher melting metals or alloys in the lower melting metals or alloys.

X-ray diffraction studies showed that substances with a GeTe content of 90% or more have a rhombohedral crystal structure with a lattice angle of almost 90 °, while substances with a GeTe content of 75% or less have a face-centered cubic crystal structure. Both crystal structures were observed in substances with a GeTe content between 75 and 90%. Thus, there is reason to believe that both types of crystal structure are required for optimal results. Nevertheless, the optimal ZT values deviate from the mean observed value ZT and indicate that to achieve optimal results, the two types of crystal must also be present in unequal amounts, as can be seen from the peaks at about 80 and 85% GeTe, respectively. It should be noted that there are ZT values between 80 and 85 mol percent GeTe which are below the ZT values which can be derived on the basis of the prior art to date. The double peaks of the ZT curve is an extremely unusual phenomenon. Examination of alloys with 85 or 80% GeTe content under the electron microscope show that the former alloy has a less ordered crystal structure than the latter.

Preliminary investigations indicate that a slight shrinkage of the crystal lattice in the immediate Near the area with a GeTe content of 85% occurs, which to a certain extent the the alloy's exceptional mechanical stability is explained.

The graphs in FIG. 2, 3 and 4 are mainly used for a better understanding of the graphic representations in FIGS. 5 and 6. Therefore, the images 2, 3 and 4 are not explained in more detail here. The graphic representation of the efficiency, ie the generally customary evaluation of the thermoelectric performance in FIG. 5, clearly illustrates the peaks of the thermoelectric efficiency in the two ranges 80% GeTe to 20% AgSbTe ₂ and 85% GeTe to 15% AgSbTe ₂ . The peak formation in the efficiency at these two points clearly shows a clear and unexpected deviation from the curve of the previously known substances, which was extrapolated on the basis of a GeTe proportion of 50, 75, 90 and 100%. In addition, it should be noted that in the higher, preferred operating range ⁰ to 750 K, the largest deviation for substances with a GeTe-content of 80 to 85% is recorded. The measurement results from FIG. 5 were used to determine the values in FIG. 6 is based on. This figure illustrates the remarkable superiority of the new alloys of the present invention over p-type thermocouples made of lead telluride which have heretofore been widely used in thermoelectric devices.

Fig. 6 is characteristic because it shows the exceptionally high thermoelectric conversion of these alloys at conventional operating temperatures. So z. B. at a temperature of 428 ° C (900 ⁰ F) at the hot solder joint (measuring point) and a temperature of 38 ° C (100 ⁰ F) at the cold solder joint (reference point) the thermoelectric power approximately 10%. The efficiency is therefore significantly higher than the 4 to 8% achieved with the substances known up to now in conventional thermoelectric devices.

In view of the known inadequacies of thermocouples of conventional compositions Samples of the alloys according to the invention were produced from Ag, Sb, Te and Ge, according to which, The procedures given were comparative tests with samples of p-type lead telluride of the same size and subjected to shape. The lead telluride was obtained from a well-known manufacturing company that produces Manufacture of thermocouples using cold pressing and sintering processes.

The samples were subjected to compressive stress tests in accordance with the usual test methods.

These tests carried out on the two substances illustrate a considerable difference in the compressive strength of lead telluride on the one hand and the new alloy with a GeTe content of 85% on the other. All four lead telluride samples broke when the samples were subjected to a pressure of between 850 and 1000 kp / cm ² . On the other hand, the samples made from the alloy according to the invention by hot pressing withstood these compressive stresses, showed ^{only slight flaking at the edges at around 1000 to 2000 kp / cm 2} and only broke when subjected to a load of around 1400 to 2500 kp / cm ² . Cast samples of the alloy according to the invention showed flaking at about 1300 to 1500 kgf / cm. Complete destruction occurred at around 1400 to 1600 kgf / cm ² . This means that the compressive strength of the new alloy is roughly twice that of lead telluride.

Samples of the two fabrics were also subjected to impact testing using known methods subjected. The new hot-pressed alloy showed after ten blows on each specimen no effect, while the cast elements of the same material after six blows were destroyed. In contrast, all of the lead telluride samples showed the first one Impact cracks and completely broke apart on the second. The impact strength tests thus again demonstrated one significant superiority of the new alloy over the commercially available compositions of Lead telluride.

Experiments with other related compositions of Ag, Sb, Ge and Te have shown significant results mechanical damage to the elements in the event of periodically changing thermal loads. In addition it should be noted that damage due to thermal cycling in fabrics with a high linear thermal expansion coefficients are more likely. Using standard dilatometric methods measurements were made on samples both of the invention and of the corresponding ones known alloys. The results obtained are shown in Table II.

Table II

Average coefficient of the linear
Thermal expansion from room temperature to 300 ° C

Mole percent GeTe Expansion coefficient in the alloy ΙΟ- ⁸ cm / cm ⁰ C 75 21.3 80 18.5 83 15.6 85 14.1 87 16.1 90 17.9

It can be seen that the new alloy with a GeTe proportion of 80% has a somewhat higher efficiency ZT at certain operating temperatures than the other new alloy with a GeTe proportion of 85%. However, the latter fabric's better resistance to periodic thermal stress makes its use for many purposes more appropriate. So were z. B. Samples with a GeTe content of 85 mole percent and an AgSbTe ₂ content of 15 mole percent were heated and cooled more than 25 times at a rate of 50 ° C. per minute without any mechanical defects being revealed.

The hot and cold pole pieces of the thermocouple (Fig. 1) are to be selected from the substances which have good electrical and thermal conductivity and which are both chemically and physically with the p-conducting thermocouple described here and the η-conductive thermocouple to be used in connection therewith are compatible. When Pole shoe material is made up of substances contained in the lead telluride-based thermocouples Find uses, such as iron, molybdenum, tungsten and tantalum.

Thermoelectric devices employing a p-type element of the type described herein were able to use an η-type element made of lead-tin-telluride with a pole piece can be made from iron at the hot end with good success. Those made from the new alloy Thermocouples were soldered with bismuth tellurium solder and tin tellurium solder with the iron shoe and to Soldering the lead-tin telluride element to the A nickel solder was used for the iron shoe. Several of these facilities were longer than 1000 hours kept in operation and brought output powers that were significantly above those that result from the usual Let substances reach a temperature difference of 400 ° K and the hot side to about 750 ° K. The material for the pole pieces of these designs was made by the Crucible Steel Company of America ”in Pittsburgh, Pennsylvania, and bears the trade name“ Ferrovac E ”.

Furthermore, a thermoelectric device consisting of a p-type element composed of 85 mole percent GeTe and 15 mole percent AgSbTe ₂ and an η-type element made of lead-tin-telluride of a commercially available type, with another compatible hot pole piece for the duration of about Operated for 7000 hours without any deterioration in electrical performance.

Although the in F i g. 6 examinations shown as η-conductive element a lead-telluride alloy with lead iodide was used for the thermoelectric device because it was previously in contact with a p-type lead telluride element with sodium had been used, it was found that

ao the p-type thermocouple from the invention Alloy with good success in connection with other known η-conducting thermocouples can be summarized in thermoelectric devices. So the new alloy z. B.

can be used as a p-conductive branch of a thermoelectric device easily and with good success together with an η-conductive branch made of lead-tin telluride with lead iodide, which is known to be suitable for this application. Typically lead, tin, tellurium and the dopant lead iodide would have to be present in such an n-type branch in a molecular ratio of 0.85: 0.15: 1.0: 0.000625.
From the preceding statements it follows

before that so far nobody made an alloy

Ag -Sb -Ge-Te

with a crystal structure that contains both rhombohedral and face-centered cubic crystals. No alloy has been prepared, the at 75O ⁰ K a ΖΓ value of about 1.3 or higher such. B. 1.4 or 1.5 has. According to the previous state of the art, no such alloys are known whose expansion

coefficients, expressed as 10 ~ ^e cm / cm- ⁰ C, are less than 15.0 or 16.0, e.g. B. the expansion coefficient 14.1 for an alloy with a GeTe proportion of 85%, the expansion coefficient 21.3 for alloys with a GeTe proportion of 75% and the expansion coefficient 17.9 for alloys with a GeTe proportion of 90 % as the most similar known Ag-Sb-Ge-Te alloys of this type can be compared. Thermocouples with such properties have not yet been produced

has been presented.

For this purpose 2 sheets of drawings

309 618/151

Claims (5)

1 ■ '■'. ". ' 2 ■ '· ■' ■ '"■' '- ·' '■■■ patent claims: whose .application for commercial purposes ■ in this' temperature range is currently 1. Alloy consisting of GeTe _{and AgSbTe 2 is known.} ^ ₁ . tion, characterized in that it is the object of the present invention ^for 5 reasons to create new _{85 mol percent GeTe and alloys consisting of GeTe and AgSbTe 2} and alloys with superior mechanical and 15 mol percent AgSbTe ₂ or thermoelectric properties that they 80 mole percent GeTe and as superior thermocouples in thermoelectric 20 mole percent AgSbTe., Make devices acceptable whose resistance persists, ίο ability in the temperature range of their solid aggregate 2. Use of an alloy that is guaranteed together and its mechanical setting according to claim 1-. as p'-conducting, leg,. strength under physical stress, such as a thermoelectric element. e.g. thermal shock and periodically changing 3. Use of an alloy of the combined temperatures normally used during preparation according to claim 1 as p-conductive leg 15 turn of thermoelectric devices occur, a thermoelectric element whose n-line is not impaired. tender leg made of a known at sicji. This is according to the invention by means of an alloy Alloy of lead-tin-telluride with lead iodide, which is achieved from Doping or from lead telluride with lead iodide- o ^ »* ■ ^ m, Endowment University exists. . ,. ao »5 mole percent GeTe and,. 4. Process for the production of an alloy 15 Mo percent AgSbTe ₂ or from
the composition of claim 1, characterized by ^ O Mo percent GeTe and
characterized that the melt 1.6 hours at,,, ^ U mol percent Ag ^ bIe ₂ 600 ° C is annealed. consists. 5. The method according to claim 4, characterized in that there are advantageous uses of this alloy indicates that after tempering, the in the subclaims. rigid alloy crushed and a sintering The alloy obtained on the basis of this invention treatment consisting of a cold pressing wrestling belong to the same type of almost degenerate with a pressure of 4000 kp / cm ² and a semiconductor, such as the related known, alloy Hot pressing at 525 ° C with a pressure of 3 ° rungeri, namely to the p-conductors. 350 kp / cm ² over a period of 30 minutes, the properties of the alloy according to the invention is subjected. have been wrestled with the most analog ones so far known alloys compared to the. essential - ^; · Borrowed advancement in the art through the