Phase stability and thermoelectric properties of alkali-metal doped group IV clathrate compounds

The relationship between phase stability and structure of alkali metal doped clathrate compounds of C, Si and Ge is investigated by a combination of first principles band structure calculations and qualitative tight binding theory. The current study of compounds of the general formula A _nX_m (A=alkali metal, X=group IV element) is to develop principles to design, via computer simulation, new and more efficient thermoelectric materials. It is found that X₄₀ and X₁₇₂ may also form stable compounds which are energetically similar to those for known materials. These new phases are characterized by calculation of Seebeck coefficient which indicates that favorable conditions for high thermoelectric efficiency exist in these phases at low dopant concentrations.