Enhanced thermoelectric performance of Mg2Si1−xSnx codoped with Bi and Cr

Abstract

Magnesium silicides are favorable thermoelectric materials considering resource abundance and cost. Chromium (Cr) doping in magnesium silicides has not yet been explored. Using first-principles calculations, we have studied the stability of Mg2Si with chromium (1.85, 3.7, 5.55 and 6.25%Cr) and tin (12.5 and 50%Sn). Three Mg2Si compounds doped with Sn, (Sn+Bi), and (Sn+Bi+Cr) are used to explain doping effects on thermoelectric performance. Notably, Cr behaves non-magnetically for ≤ 2%Cr, after which ferromagnetic ordering is favored (≤12.96%Cr), despite its elemental antiferromagnetic state. With alloying of Sn (70.4%), Mg2Si remains an indirect-bandgap semiconductor, but adding small amounts of Bi (3.7%) increases the carrier concentration such that electrons occupy conduction bands, making it a degenerate semiconductor. Mg2Si0.296Sn0.666Bi0.037 is found to give the highest thermoelectric figure of merit (ZT) and power factor (PF) at 700 K, i.e., 1.75 and 7.04 mW m −1 K −2 , respectively. Adding small %Cr decreases ZT and PF to 0.78 and 4.33 mW m −1 K −2 , respectively. Such a degradation in TE performance is attributed to two factors: (i) uniform doping acting as an electron acceptor, decreasing conduction, and (ii) the loss of low-lying conduction band degeneracy with doping, decreasing the Seebeck coefficients. A study of configurations of Cr doping suggests that Cr has a tendency to form clusters inside the lattice which play a crucial role in tuning the magnetic and TE performance of doped-Mg2Si compounds.

Thermoelectric and Mechanical Properties of Environmentally Friendly Mg2Si0.3Sn0.67Bi0.03/SiC Composites

“…The search for improved thermoelectric materials, TE, has recently accelerated because of advances in materials synthesis and processing. − Magnesium silicide based materials have shown high potential as thermoelectrics, a consequence of their large Seebeck coefficient, high electrical conductivity, thermal stability, and last but not least their low toxicity and abundance of their constituent elements. − However, their relatively poor mechanical properties, such as hardness, tensile, and compression properties, so far restricted their applications.…”

Recent Progress in Multiphase Thermoelectric Materials

“…(2) introduce a magnetic dopant in a non-magnetic material [46][47][48][240][241][242][243]; (3) introduce a magnetic secondary phase in a non-magnetic material [49,50].…”

Magnetic Properties of 3d Transition Metal Atoms (V, Cr, Mn, Fe, Co, or Ni)‐Doped Mg2Si

“…To improve these properties, especially the thermoelectric property, different elements were doped into Mg 2 Si, such as Ag, [ 6 ] B, [ 7 ] Bi, [ 8,9 ] Cu, [ 10 ] Li, [ 11 ] P, [ 12 ] Sb, [ 13,14 ] Y, [ 15 ] rare earth elements, [ 16 ] and codoped strategy. [ 17,18 ] Undoped Mg 2 Si is well known as a nonmagnetic semiconductor. [ 19 ] However, as far as we know, there are few studies on the magnetic properties of doped Mg 2 Si, except for Kim, [ 20 ] Vikram, [ 17 ] Ahmar, [ 21 ] and our group.…”

“…[ 17,18 ] Undoped Mg 2 Si is well known as a nonmagnetic semiconductor. [ 19 ] However, as far as we know, there are few studies on the magnetic properties of doped Mg 2 Si, except for Kim, [ 20 ] Vikram, [ 17 ] Ahmar, [ 21 ] and our group. [ 22 ]…”