First principles investigation of thermoelectric materials

Abstract

Thermoelectric TE materials have attracted particular attention in the last decade because they act as a 8216 green 8217 way of converting waste heat energy to electrical energy through the Seebeck effect The efficiency of a thermoelectric device is measured by the dimensionless figure of merit ZT which is directly proportional to the square of Seebeck coefficient electrical conductivity and inversely proportional to thermal conductivity Depending on the operational temperatures materials like bismuth telluride lead halides MgAgSb skutterudites and copper and tin chalcogenides are promising candidates for use in thermoelectric devices To the best of our knowledge the highest reported value of ZT is about 2 6 at 573 K which is observed for cadmium doped AgSbTe2 Hence there are still efforts to improve design novel materials with high ZT Improving ZT implies that one needs to increase the Seebeck coefficient and electrical conductivity and reduce thermal conductivity However the mechanisms that improve one of them deteriorate the other thereby making it challenging to design novel materials with improved ZT Over the last several years many strategies like nano structuring band structure engineering heterostructure formation dimensionality reduction etc have been developed to improve ZT In addition to experimental techniques computational materials design is also an important tool for the discovery of novel thermoelectric materials In this thesis using computational tools like density functional theory semiclassical Boltzmann theory and many body electron phonon coupling we have studied two aspects of computational research in thermoelectric materials In the first part of the thesis we have used computational tools to study the effect of structural modifications on transport properties of bulk and layered materials Amongst bulk materials we have studied how doping copper chalcogenides BaCu2Se2 with suitable dopants introduce resonant states band engineering to improve the power factor Be newline newline