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Previously, the Institute of Thermoelectricity has created Bi 2 Te 3 -based modules with an efficiency of $7% in the temperature range of 30°C to 300°C, with legs that employed homogeneous thermoelectric materials. Herein, we present the results of development of such modules with legs made of inhomogeneous materials. Based on the theory of optimal control and object-oriented computer technology, programs to determine the requirements for material properties in the inhomogeneous legs were created. It was established that introduction of inhomogeneity in the form of continuous and step changes in three-segment n-and p-type legs yields almost identical efficiency increases of about 15%. Use of two segments reduces this value of 10% to 12%. Modules with twosegment legs encapsulated in thin-walled metal cases filled with inert gas have been built, yielding improved efficiency of 7.8% to 8%.

The theoretical aspects of evaluating the electrical resistance of a thermoelectric leg–metal contact are considered. A physical model of such a contact and methods for calculating the main components of the contact resistivity, namely, the resistivity of the interfacial layer and the resistivity related to the transfer of charge carriers through a potential barrier at the boundary between a material of the thermoelectric leg and a metal, are proposed. The contact resistivity for thermoelectric legs made of Bi2Te3 based materials with deposited antidiffusion nickel layers is calculated. It was established that the contact resistivity in such thermoelements reaches a value from 0.25 × 10−6 to 2.5 × 10−6 Ω cm2 and depends on the temperature and interfacial layer thickness. It is demonstrated that the findings are in good agreement with the known experimental values of contact resistivity.

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