Thermoelectric performance enhancement of Mg₂Sn based solid solutions by band convergence and phonon scattering via Pb and Si/Ge substitution for Sn

Abstract

In this study, the thermoelectric properties of Mg2Sn0.98-xPbxSb0.02 were first studied, and then Mg2Sn0.93-xSixPb0.05Sb0.02 and Mg2Sn0.93-xGexPb0.05Sb0.02 were accordingly investigated. The results showed that the formation of Mg2Sn0.98-xPbxSb0.02 solid solutions effectively reduced the lattice thermal conductivity of Mg2Sn. The room temperature lattice thermal conductivity of Mg2Sn0.98Sb0.02 is ∼5.2 W m(-1) K(-1) but only ∼2.5 W m(-1) K(-1) for Mg2Sn0.73Pb0.25Sb0.02, a reduction of ∼52%. Further alloying Mg2Sn0.98-xPbxSb0.02 with Mg2Si or Mg2Ge to form Mg2Sn0.93-xSixPb0.05Sb0.02 or Mg2Sn0.93-xGexPb0.05Sb0.02 reduced the lattice thermal conductivity significantly due to enhanced phonon scattering by point defects as well as nanoparticles. Moreover, bipolar thermal conductivities were suppressed due to the larger bandgap of Mg2Si and Mg2Ge than Mg2Sn. Furthermore, similar to the pseudo-binary Mg2Sn-Mg2Si and Mg2Sn-Mg2Ge systems, band convergence was also observed in pseudo-ternary Mg2Sn0.93-xSixPb0.05Sb0.02 and Mg2Sn0.93-xGexPb0.05Sb0.02 materials. The convergence of conduction bands led to higher PFs at lower temperatures for Mg2Sn0.93-xSixPb0.05Sb0.02 and Mg2Sn0.93-xGexPb0.05Sb0.02 materials. As a result, higher peak ZTs of ∼1.3 for Mg2Sn0.63Si0.3Pb0.05Sb0.02 and ∼1.2 for Mg2Sn0.68Ge0.25Pb0.05Sb0.02 were achieved.

Control of the Thermoelectric Properties of Mg2Sn Single Crystals via Point-Defect Engineering

“…In the present study, we focus on Mg 2 Sn with the same crystal structure as Mg 2 Si. Mg 2 Sn has been studied extensively as a potential TE material [18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37] . Xin et al 31 reported that an Sb-doped n-type polycrystalline Mg 2 Sn, Mg 2.15 Sn 0.98 Sb 0.02 exhibited a zT value of 0.53 at 650 K (κ and PF are 4.7 W/mK and 3.9 W/mK 2 , respectively).…”

“…Despite these sufficiently high PF values, the κ values are also high, limiting the zT values lower than ~0.5. Although the importance of controlling point defects in Mg 2 Sn is highlighted in some literature 29,31 , quantitative analysis of point defects has not been performed so far.…”

Thermoelectric performance of Li doped, p-type Mg2(Ge,Sn) and comparison with Mg2(Si,Sn)

“…The Lorenz number is used to calculate the lattice thermal conductivity lat + bi = − e = − . For the calculations we have assumed a scattering parameter of = −0.5, corresponding to carrier scattering by acoustic phonons beingdominant, an assumption that is considered to be well fulfilled for the material at temperatures above 300 K [8,13,48,51].…”

Phonon scattering by nanoscale twin boundaries

“…Phonons can be effectively scattered by crystal defects and nanostructures, e.g., point defects [1][2][3][4][5][6][7][8][9][10][11][12], dislocations [13][14][15][16][17][18], grain boundaries [19][20][21][22][23], and nanoparticles/nanoprecipitates [24][25][26][27][28][29][30][31][32]. As one kind of defects, twins, which are often been observed in various material systems [33][34][35][36][37][38], its effect on phonon scattering is much less investigated comparing to other defects.…”