Enhanced Thermoelectric Performance in Mg₂Si by Functionalized Co‐Doping

Abstract

Mg2Si specimens doped with Bi, Al, and Se are synthesized via induction melting followed by rapid compaction using an induction assisted hot‐uniaxial press. Phase formation, dopant solubility, and microstructure are studied using X‐Ray diffraction and scanning electron microscopy. Results indicate the presence of the dopants to varying extent in the Mg2Si matrix, which is reflected in the lattice parameter and charge carrier concentration values. Temperature dependent thermoelectric properties are measured between room temperature and 673 K. Se is observed to enhance the density of states (DOS) effective mass (mnormalD*), while Al increased the carrier mobility (μ). Best thermoelectric performance are obtained for co‐doped Bi,Se and Bi,Al compositions with ≈20% increase in engineering figure of merit, ZTeng (ΔT = 350 K) compared to only Bi doped specimen. This enhancement can be explained from the observed electronic (increased mnormalD* due to Se incorporation) and microstructural (μ increase in Al containing compositions due to lower grain boundary magnesium oxide layer)characteristics of the specimens. Also, grain boundary accumulation (of Bi) is observed in Bi doped samples which results in a lowering of the lattice thermal conductivity, κnormalL.

Systematic analysis of the interplay between synthesis route, microstructure, and thermoelectric performance in p-type Mg2Si0.2Sn0.8

“…Thermoelectric materials with high include, among others, nanostructured PbTe [3], CoSb 3 -based Skutterudites [4], half-Heusler compounds [5,6], Zintl phases [7] and Mg 2 Sibased solid solutions [8]. Thermoelectric materials are synthesized by various synthesis techniques such as melting of the elements followed by slow cooling and long-time annealing [9], multi-step solid-state reaction [10,11], self-propagating high temperature synthesis [12,13], mechanical alloying [14,15], induction melting [16][17][18], spark plasma sintering [19], melt-spinning, or combinations of these techniques followed by a compaction process [20,21]. The synthesis route affects the thermoelectric performance of a material in a complex fashion: temperature can govern carrier concentration through dopant solubility or temperature dependent loss mechanisms (evaporation, oxidation, precipitation); carrier mobility and lattice thermal conductivity are strongly influenced by the microstructure of the sample.…”

“…Using the well-established single parabolic band (SPB) model, we have systematically investigated the differences of Li-doped Mg 2 Si 0.2 Sn 0.8 fabricated by two popular synthesis routes: high energy ball milling (BM) and induction melting (IM) [14,18,42]. The composition was chosen because Li is the most efficient dopant for p-type Mg 2 Si 1-x Sn x and the samples with x = 0.8 have similar efficiency as the samples with x = 0.6 but a higher power factor [32,43]; they are also further outside the reported miscibility gap which is important for long term stability [44][45][46].…”

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.…”

Generic Approach for Contacting Thermoelectric Solid Solutions: Case Study in n- and p-Type Mg2Si0.3Sn0.7

“…Keeping this in mind, we propose a multilayer strategy wherein contacting can be achieved in a wide range of material compositions using the same contact material. The proposed strategy is also generic in the sense that it might be extended to other TE solid solution systems such as GeTe, , PbTe, Bi 2 Te 3 , and silicides. , The multilayer technique is discussed in the next section, and its applicability has been demonstrated in n- and p-doped Mg 2 Si 0.3 Sn 0.7 , which is a potential material for midtemperature power generation. − A well-bonded crack-free interface has been observed in both n- and p-doped materials with excellent contact resistance values (<20 μΩ cm 2 ).…”