US3530008A - Thermo-e.m.f. generator consisting of a single crystal anisotropic cadmium antimonide - Google Patents

Description

Sept. 22, 1970 A. G. SAMOILOVEQH 3,539fl08 THERMO-E.M.F. GENERATOR CONSISTING OF A SINGLE CRYSTAL ANISOTROPIC CADMIUM ANTIMONIDE Filed Jan. 26, 1967 PM. i

Patented Sept. 22, 1970 3,530,008 THERMO-E.M.F. GENERATOR CONSISTING OF A SINGLE CRYSTAL ANISOTROPIC CADMIUM ANTIMONIDE Anatoly Grigorievich Samoilovich, Ulitsa Universitetskaya 13, kv. 4; Izrail Moiseevich Pilat, Ulitsa Zankovetskaya 15, kv. and Lukyan Ivanovich Anatychuk, Ulitsa Russkaya 95, all of Chernovtsy, U.S.S.R.

Filed Jan. 26, 1967, Ser. No. 611,993 Int. Cl. H01v 1/06, 1/30; H02n 4/00 US. Cl. 136-200 2 Claims ABSTRACT OF THE DISCLOSURE This invention relates to devices for converting thermal energy into electrical energy and, more particularly, it relates to thermoelements.

In the known thermoelements (thermocouples) the availability of two conductors made from dissimilar materials and the existence of a temperature gradient are the prerequisites of thermo-E.M.F. generation. (cf. A.F. Ioffe Semiconductor Thermoelements, USSR Academy of Science Publ. House.)

However, prior art thermoelements comprised of either metals or semiconductors have a number of disadvantages which are inherent in all the thermoelements of this type and manifest themselves to a greater or lesser extent in every specific application. Among said disadvantages mention may be made of interdiffusion of conductors, of back thermo-E.M.F. due to mixed conductivity phenomena, and of transient resistances at conductor junctions (the phenomenon of thermoelements commutation).

The phenomena associated with said disadvantages decrease the efficiency of thermoelements and, sometimes hinder their use.

It is an object of the present invention to eliminate the aforementioned disadvantages.

It is another object of the present invention to provide a small-size thermoelement having high sensitivity.

It is a further object of the present invention to provide a thermoelement with enhanced reliability due to the absence of commutation junctions.

It is an additional object of the present invention to provide a thermoelement which is convenient in operation and will have along service life.

In accordance with these and other objects, the present invention provides a thermoelement made in the form of a single crystal noted for its anisotropic thermo-E.M.F. property at least in two directions at right angles, wherein the direction of anisotropy is selected so as to be oriented at an angle relative to the temperature gradient applied, said gradient being at right angles to the generated which depends upon the material and geometric dimensions of the crystal used, and also upon the temperature difference applied.

The present invention is illustrated hereinbelow by the description of an exemplary embodiment with reference to the appended drawing, wherein:

FIG. 1 is a cross-sectional view of a single crystal with denoted XY-axes and the direction of thermo-E.M.F. anisotropy, and

FIG. 2 illustrates the theoretical and experimental de pendence of the upon the temperature gradient applied for a thermopile comprised of single crystals.

Let us consider a single crystal having anisotropic thermo-E.M.F. properties. Generally, the tensor of thermo may consist of several components. For the sake of simplicity, we assume that the tensor of thermo-EM.F. is comprised of two different components, i.e., the thermois dilferent in two directions at right angles. The anisotropy of thermo-E.M.F. is conventionally associated with crystallographic directions. Let the components a and 0: of the tensor denote the thermo-E.M.F. that develops along the and [010] crystallographic directions (FIG. 1) respectively when a temperature gradient is maintained in these same directions. Discussed hereinbelow is the case when the temperature gradient in the crystal is arbitrarily directed in relation to the crystal-- lographic axes and is in the plane of these axes. The angle (p represents the angle between the X axis and the [001] direction.

The temperature gradient is directed along the Y-axis. It can be demonstrated that due to the anisotropy of thermo-E.M.F., there arises along the X axis the E.M.F., E given by the formula 6 2) where: T and T denote temperatures on the opposite crystal faces and b is the length of the crystal along the Y-axis (thickness).

It follows from the Formula 2 that the magnitude of generated thermo-E.M.F. depends not only on the properties of the material used and temperature difference, as is the case in ordinary thermoelements, but is proportional to the length a of the crystal and inversely proportional to the thickness b of the crystal. The desired magnitude of thermo-E.M.F. may, therefore, be obtained, all other conditions being equal, by selecting an appropriate size of the thermoelements in question, so that earlier limitations imposed on the magnitude of the thermoare eliminated and a high thermo-E.M.F. can be attained.

A thermoelement from a single crystal of cadmium antimonide, CdSb, has been prepared by following the principle disclosed hereinabove.

The thermo-E.M.F. of CdSb single crystals has been found to be anisotropic.

Investigations of thermo-E.M.F. in the [100] and [010] directions have been carried out in the temperature range of from 100 K. to 400 K. on specimens from two different ingots prepared by zone recrystallization. Maximum anisotropy is observed at temperatures above 300 K. at which eigenconduction commences. The maximum value of a a is as high as 150 V degf A series of anisotropic thermoelements has been prepared from CdSb single crystals grown so as to obtain a specified crystallographic orientation. Maximum at a temperature difference of T T K. is as high as 0.1 v. It is, therefore, feasible to construct from such thermoele'ments a pile which makes possible the generation of adequately high voltages at low temperature gradients and for relatively modest overall dimensions of the pile.

A pile was manufactured from 8 elements, each having the following dimensions in mm.: a=9, 12:0.7, and :12. The maximum total weight of the elements amounted to 0.5 g. The elements were mounted on a copper block which served to dissipate heat. The thermopile was tested under the following conditions: one face of the pile was maintained at a temperature of 296 K., while the temperature of the other face was determined by a heater and varied from room temperature to 410 C. To measure the temperature, use was made of copperconstantan thermocouples. Presented in FIG. 2 are the results of tests (curve A). At T -T =1l6 K. the maximum E.M.F. generated by the pile amounted to 1.1 v.

It is to be noted that appropriate doping of the starting material and selection of the pile size in conformity with specific applications are conducive to attaining better performance characteristics. In the pile disclosed hereinabove no exhaustive use was made of the potentialities offered by the present invention for the generation of high electromotive forces. For example, the temperature gradient applied may be increased. Another means of increasing the consists in decreasing the thickness and increasing the length of the elements.

The results obtained are in good agreement with the values calculated by the Formula 2 (FIG. 2, curve C). Some divergence between the observed and calculated values is due to the fact that the temperature dependence of the thermowas assumed to be constant (a u 150 v./ deg.) over the entire temperature range.

To manufacture thermoelements, recourse may be had to single crystals of the following materials exhibiting the anisotropy of thermo-E.M.F.: bismuth, bismuth-antimony solid solutions, graphite, zinc-antimony, and chromium silicides.

The anisotropic piles may be useful in diverse radio appliances requiring high voltages at low currents and low temperature gradients. The thermopiles of the present invention may likewise be employed as power sources in ionization tubes of elementary particle counters and as sensitive temperature difference transducers in various automatic instruments.

We claim:

1. A thermo-E.M.F. generator consisting of a single crystal of cadmium antimonide having thermo-E.M.F. anisotropy in at least two directions at right angles; means for applying a temperature gradient to said crystal at an angle with respect to one of the directions of anisotropy of the thermo-E.M.F. for generating an in a direction normal to the direction of the applied temperature gradient; and means for removing current in a direction perpendicular to the temperature gradient, said E.M.F. being given by the following formula:

dT E,= sin 2 --a M 11 22) dy wherein wherein:

T -T 1 is the temperature difference at the ends of the crystal in the Y-direction; and b is the length of the crystal in the Y-direction.

References Cited UNITED STATES PATENTS 2,685,608 8/1954 Justi l36240 2,990,439 6/1961 Goldsmid et al. 136236 3,090,207 5/1963 Smith et al. 136-240 3,136,134 6/1964 Smith 136240 FOREIGN PATENTS 1,088,764 10/1967 Great Britain.

OTHER REFERENCES Harman et al. (I): Journal of Applied Physics, vol. 34, January 1963, pp. 189-194.

Harman et al. (II) Journal of Applied Physics, vol. 34, August 1963. pp. 2225-2229.

Sausoilovich et al.: Phys. Stat. 801., vol. 16, 1966, pp. 459-465.

Anatychuk et al.: Uke. Fiz. Fh., vol. 11(9) pp. 971-7 (1966).

Boerdijk: Journal of Applied Physics, vol. 30(7), July 1959, pp. 1080-1083.

Ertl et al.: Brit. J. Appl. Phys., vol. 14, (1963) pp. 161 and 162.

Hruby et al.: Chem. Abs., vol. 63, No. 15665h.

Gusev et al. In. Thermoelectric Properties of Semiconductors, Kutasov (ed.) consultants Bureau New York, 1964, pp. 50-53.

Pilat et al.: Ibid pp. 47-49.

Wolf et al. Proc. International Conf. on Physics of Semic0nductors..Exeter. July 1962. pp. Title, 771-776.

WINSTON A. DOUGLAS, Primary Examiner A. M. BEKELMAN, Assistant Examiner US. Cl. XJR.

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