SOLID STATE and CLUSTER PHYSICS Annual Report 2001 Universität Konstanz
- Fachbereich Physik
The Tl5Te3 related compounds have recently been discovered as very efficient materials for thermoelectric applications [Wolfing00]. In this work, techniques have been investigated to further optimize materials in this group. The compound Tl9SbTe6 was characterized and found to exhibit very good thermoelectric performance, although it stays behind Tl9BiTe6, which still has to be considered as the best ternary compound in the Tl5Te3 group. Investigations on the Tl9SbTe6–Tl9BiTe6 alloy system have been carried out in order to optimize the electronic properties and lower the lattice thermal conductivity. Measurements and theoretical estimations show that an optimized material must be at or close to the Tl9BiTe6 end of the system. The expected improvement due to a reduction of the thermal conductivity by alloy scattering, however, was not observed. A study on the effect of doping in Tl9BiTe6 was carried out. By doping with bismuth n-type Tl9BiTe6 could be prepared, which would be necessary for a thermoelectric device that is solely based on Tl9BiTe6. Unfortunately, n-type Tl9BiTe6 was found to have much weaker thermoelectric performance than its p-type counterpart. Doping experiments with HgTe showed that p-type doping can improve the performance of Tl9BiTe6. However, a significant embrittlement has been observed on this material, that limits its use in actual devices. Further optimization of the doping technique and/or the dopant itself are expected to solve these problems and enhance the performance of Tl9BiTe6. In additional investigations YNiSband Zr3Ni3Sb4-related compounds have been screened for their thermoelectric properties. The members of both groups exhibit high thermopowers and have low thermal conductivities. The high electrical resistivity, however, limits the thermoelectric performance. Nevertheless, further research in related systems seems promising.