Development of Environmentally-Friendly High Power Density Thermoelectric Module by using Titanium Alloys

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The effectiveness of a material for thermoelectric applications is determined by the dimensionless figure of merit ZT, where T is the absolute temperature and Z=(S^2σ)/k (S is the Seebeck coefficient, a the electrical conductivity, and k the thermal conductivity). We have taken particular note of 18 electron half-Heusler compounds as new thermoelectric materials because of their semiconductor like band structure. In the present study, in order to develop an environmentally-friendly high-density thermoelectric module, we studied titanium-based half-Heusler alloys as advanced thermoelectric materials.For n-type materials, we have succeeded in developing high ZT materials by doping Nb on the Ti or Zr site of (Ti, Zr)NiSn half-Heusler compounds. The maximum ZT value is 0.7 obtained at 970 K. For p-type materials, Sn-doped (Ti, Zr)CoSb exhibited relatively high ZT values ; the maximum is 0.46 obtained at 960 K. It can be concluded that the titanium based half-Heusler compounds have a potential to be good thermoelectric materials at high temperature around 1000 K.