Electronic structure and thermoelectric properties of p-type Ag-doped Mg2Sn and Mg2Sn1-xSix (x = 0.05, 0.1)

Abstract

An experimental and theoretical study of p-type Ag-doped Mg2Sn and Mg2Sn1-xSix (x = 0.05, 0.1) is presented. Band structure calculations show that behavior of Ag in Mg2Sn depends on the site it occupies. Based on Bloch spectral functions and density of states calculations, we show that if Ag substitutes for Sn, it is likely to form a resonant level; if it substitutes for Mg, a rigid-band-like behavior is observed. In both cases, the doped system should exhibit p-type conductivity. Experimentally, thermoelectric, thermomagnetic, and galvanomagnetic properties are investigated of p-type Mg2Sn1−xSix (x = 0, 0.05, 0.1) samples synthesized by a co-melting method in sealed crucibles. Ag effectively dopes the samples p-type, and thermoelectric power factors in excess of 20 μW cm−1K−2 are observed in optimally doped samples. From the measured Seebeck coefficient, Nernst coefficient, and mobility, we find that the combination of acoustic phonon scattering, optical phonon scattering and defect scattering results in an energy-independent scattering rate. No resonant-like increase in thermopower is observed, which correlates well with electronic structure calculations assuming the location of Ag on Mg site.

Analyzing transport properties of p-type Mg2Si–Mg2Sn solid solutions: optimization of thermoelectric performance and insight into the electronic band structure

“…Previous works have reported on p-type Mg 2 Si 1-x Sn x using Ag [15][16][17][18][19][20], Li [21][22][23][24][25][26], Ga [27,28], and Na [29] as single dopants; a studying using double doping was also presented [30]. The highest of 0.7 has been reported for Li-doped samples [13,23], possibly because of the high solubility of Li [13,31].…”

Valleytronics in thermoelectric materials

“…In the framework of Boltzmann transport theory with the simple parabolic band model, the Seebeck coefficient enhancement at a given carrier concentration due to resonant levels can be intuitively understood by the increased m b * , 30 which are also found from the theoretically calculated band structure diagrams. 90,95 The influence of m b * on TE performance is discussed in more details in the next section. In short, the strategy by introducing resonant levels in TE materials to obtain better valley structures would inevitably bring a tradeoff on the mobility, as larger m b * not only benefits for α but also lowers μ.…”

Thermoelectric investigation of transition metal oxide NiO 2 : A first principles study

“…The Seebeck coefficient, which indicates the amount of voltage obtained by applying temperature gradient across a material, decreases with an increase in temperature due to bipolar effect or excitation of both types of charge carriers resulting in the increase of inverse hall effect 54 . As the Seebeck coefficient is inversely proportional to the chemical potential and carrier concentration according to Mott equation 55,56 S ꞊ ε ꞊ μ , its value decreases with increase in as shown in Figure 4A. The reason being the Seebeck coefficient depends on the asymmetry of distribution function which is maximum near the Fermi level.…”