Contact Systems for Thermoelements with Operating Temperatures up to 1200 K

To increase the efficiency of thermoelectric devices, nanostructured thermoelectric materials for operation in the temperature range from 170 to 1200 K having high values of thermoelectric figure of merit were obtained. Thermoelectric materials have the following maximum values of ZT: Bi
₂
Te
_2.8
Se
_0.2
- 1.15; Bi
_0.5
Sb
_1.5
Te
₃
- 1.17; Bi
₂
Te
_2.4
Se
_0.6
- 1.16; Bi
_0.4
Sb
_1.6
Te
₃
- 1.18; PbTe - 1.31; GeTe - 1.41; SiGe - 1.23 for n-type and 1.21 for p-type. Parameter ZT is determined for the operating temperature range of each material. Increase of the figure of merit for nanostructured TEMs in comparison with the usual structure is determined by the decrease of thermal conductivity by 10-15% due to the phonon heat transfer.In order to increase the efficiency of thermoelectric generators by increasing the temperature difference between hot and cold thermoelement junctions, multisection thermoelements are used. For such a thermoelement with operating temperatures up to 1200 K, the structures and technology of contact systems obtained by vacuum deposition of thin films have been proposed and justified. The influence of the preparation of thermoelectric material surface and the structure of contact systems on their thermal stability, contact resistance and mechanical strength has been established. Effective contact systems are proposed for the temperature range from 300 to 1200 K: Ni; Mo/Ni and Mo/Ta-W-N/Ni, having an adhesive strength of at least 16.0 MPa and a contact resistance of not more than 4.9·10
^-9
Ohm·m
²
.