Defect chemistry and enhancement of thermoelectric performance in Ag-doped Sn_{1+δ−x}Ag_xTe

다국어 초록 (Multilingual Abstract)

<P>We investigated the thermoelectric properties and electronic band structure calculation of Sn1−xAgxTe and Sn1.03−xAgxTe (<I>x</I> = 1, 3, 5, 7 mol%) compounds. From the formation energy calculation, the Sn vacancy by Ag doping gives rise to the increase of carrier density as well as the decrease of lattice parameters. There are several possibilities of polar point defects and various neutral Ag complex defects (linear, orthogonal, square type defects <I>etc.</I>) which compensate the increase of charge carriers. The carrier scattering by Ag-related complex defects reduces Hall mobility, resulting in the decrease of electrical conductivity in spite of the increase of Hall carrier density by Ag doping. We do not observe any resonant level formation from the electronic band structure calculation. The change of the scattering exponent by an Ag complex defect (AgSn-AgTe-AgSn) may be associated with the increase of the Seebeck coefficient. Even if the defect scattering reduces electrical conductivity, the increase of the Seebeck coefficient and reduction of lattice thermal conductivity by Ag complex defects result in the enhancement of <I>ZT</I> value 0.62 at 800 K for the Sn-excess Sn0.96Ag0.07Te compound. It indicates that the Sn vacancy and Ag complex defects are associated with the enhancement of thermoelectric figure-of-merit in SnTe based compounds.</P>