Abstract
Thermoelectric materials were subjected to high fluence neutron irradiation in order to study the effect of radiation damage. This work is relevant to the NASA Radioisotope Thermoelectric Generator (RTG) program in which thermoelectric elements are exposed to radiation over a long period of time in space missions. It is also of interests to basic transport studies regarding the thermal and electrical properties of thermoelectrics after irradiation. Selected n-type and p-type bismuth telluride materials were irradiated at the High Flux Isotope Reactor (HFIR) with neutron fluence of 1.3 x 1018 n/cm2 (E > 0.1 MeV). The irradiated materials were activated, especially the Sb containing p-type materials. Transmutation from Bi to Po was also detected in both types of materials. The radiation levels of the samples were monitored and stored for more than three months before testing at the Low Activation Materials Development and Analysis (LAMDA) facility. The increase in Seebeck coefficient in the n-type material was partially off-set by an increase in electrical resistivity making the power factor higher at lower temperatures. For the p-type materials, although electrical properties were not affected by irradiation, the figure of merit, zT, showed a clear drop in 300-400 K range reflecting similar drops in thermal conductivity. Considering the p-type and n-type materials are connected in series in a module, the overall irradiation damages at device level were limited. These results at excessive neutron fluence than typical space missions are significant to ensure the radiation damages to thermoelectric are not going to affect the performances of RTGs. It also showed that bismuth telluride is highly resistance to irradiation and has the potential to be used in a reactor environment.
