Synergetic effect of Zn substitution on the electron and phonon transport in Mg2Si0.5Sn0.5-based thermoelectric materials

Abstract

Mg₂Si_1−xSn_x alloys are a prospective material for thermoelectric generators at moderate temperatures. The thermoelectric properties of Mg₂Si_0.5Sn_0.5-based thermoelectric materials with only Zn substitution or Zn/Sb co-doping were investigated. Isoelectronic Zn substitution did not affect the carrier concentration, but improved the carrier mobility. Zn atoms incorporated into a Sb-doped Mg₂Si_0.5Sn_0.5 matrix simultaneously boosted the power factor and suppressed the lattice thermal conductivity, leading to an enhancement of the thermoelectric figure of merit ZT of the resulting bulk materials. The interplay between the electron and phonon transport of Mg₂Si_0.5Sn_0.49Sb_0.01 substituted with Zn at Mg sites results in an enhancement of the ZT by 25% at ∼730 K, from ZT ≈ 0.8 in Mg₂Si_0.5Sn_0.49Sb_0.01 to ZT ≈ 1.0 in Mg_1.98Zn_0.02Si_0.5Sn_0.49Sb_0.01. Solid solutions in the Mg₂Si–Mg₂Sn system appear to be more promising for thermoelectric applications.