Nano thermoelectric materials

Synthesis and Characterisation of Thermoelectric Materials

Anirudha Karati

The search for newer and cleaner alternative energy sources are the need of the present day. Waste heat recovery and conversion of it into useful energy is the basis of thermoelectric materials. The efficiency of such materials is characterized by Thermoelectric figure of merit ZT=S2s/k where S=Seebeck Coefficient, s= Electrical Conductivity, k=Thermal Conductivity where k=ke + kl; ke due to electronic conduction and  kl due to lattice vibrations. For an effective thermoelectric material, the need for a material with a high S and s but low k is essential. It has been found that semiconductors are the best candidates for these materials. (Bi,Sb)2Te3, SnSe, PbTe are some of the best known thermoelectric materials. However limitations on mechanical properties, high temperature applications, toxicity and abundance are common issues that are faced by these materials and the search for newer materials is still on.

Our current research looks into Half heusler alloys for high temperature thermoelectric applications. The synthesis of these alloys are carried out by vacuum arc melting followed by ball milling to make them into nanomaterials. Nanostructuring improves the property by scattering heat carrying phonons which thereby decrease the net thermal conductivity and improves upon ZT. Research is underway to improve thermoelectric properties and correlate the properties with the microstructure in half heusler alloys. Additionally, we are also working on several antimonides and sulphides to synthesize thermoelectric materials with cheaper, less-toxic and more earth abundant elements.

XRD Pattern of TiFe0.5Ni0.5Sb

SEM image of as-cast Mg3Sb1.8Pb0.2 alloys (dark grey is Mg-Sb-Pb phase & light grey is Sb phase)