Phase Segregation and Superior Thermoelectric Properties of Mg₂Si_1–xSb_x (0 ≤ x ≤ 0.025) Prepared by Ultrafast Self-Propagating High-Temperature Synthesis

Abstract

A series of Sb-doped Mg2Si(1-x)Sb(x) compounds with the Sb content x within 0 ≤ x ≤ 0.025 were prepared by self-propagating high-temperature synthesis (SHS) combined with plasma activated sintering (PAS) method in less than 20 min. Thermodynamic parameters of the SHS process, such as adiabatic temperature, ignition temperature, combustion temperature, and propagation speed of the combustion wave, were determined for the first time. Nanoprecipitates were observed for the samples doped with Sb. Thermoelectric properties were characterized in the temperature range of 300-875 K. With the increasing content of Sb, the electrical conductivity σ rises markedly while the Seebeck coefficient α decreases, which is attributed to the increase in carrier concentration. The carrier mobility μ(H) decreases slightly with the increasing carrier concentration but remains larger than the Sb-doped samples prepared by other methods, which is ascribed to the self-purification process associated with the SHS synthesis. In spite of the increasing electrical conductivity with the increasing Sb content x, the overall thermal conductivity κ decreases on account of a significantly falled lattice thermal conductivity κ(L) due to the strong point defect scattering on Sb impurities and possibly enhanced interface scattering on nanoprecipitates. As a result, the sample with x = 0.02 achieves the thermoelectric figure of merit ZT ∼ 0.65 at 873 K, one of the highest values for the Sb-doped binary Mg2Si compounds investigated so far. A subsequent annealing treatment on the sample with x = 0.02 at 773 K for 7 days has resulted in no noticeble changes in the thermoelectric transport properties, indicating an excellent thermal stability of the compounds prepared by the SHS method. Therefore, SHS method can serve as an effective alternative fabrication route to synthesize Mg-Si based themoelectrics and some other functional materials due to the resulting high performance, perfect thermal stability, and feasible production in large scale for commercial application.

Hydrophilic Graphene Preparation from Gallic Acid Modified Graphene Oxide in Magnesium Self-Propagating High Temperature Synthesis Process

“…SHS represents an attractive alternative to conventional methods for materials synthesis 21 22 23 . This technique, which involves self-propagating reactions of either solid-solid or gas-solid type, is characterized by the fact that, once the starting mixture is ignited by means of external thermal sources for relatively short times, highly exothermic reactions propagate through the mixture in the form of self-sustained combustion wave, progressively leading to final products without requiring additional energy.…”

Multi‐Scale Microstructural Thermoelectric Materials: Transport Behavior, Non‐Equilibrium Preparation, and Applications

“…For example, zone melting, melting followed by slow cooling, melting combined with long‐time annealing, and multi‐step solid state reactions can be classified as equilibrium processes. In contrast, mechanical alloying, hot deformation, melt spinning (MS), and the self‐propagating high‐temperature synthesis (SHS) are typical examples of non‐equilibrium processes. In this section, we emphasize two non‐equilibrium synthesis approaches: melt spinning and SHS.…”

“…Combining SHS with subsequent PAS processing, several excellent bulk TE materials, including Cu 2 Se, Bi 2 Te 3 ‐based alloys, skutterudites, SnTe, ZrNiSn, Cu 2 SnSe 3 , and Mg 2 Si 1– x Sn x were prepared . Taking Cu 2 Se as an example, and as discerned from the infrared images shown in Figure a, the SHS process in Cu 2 Se can be classified into three main stages: i) local ignition, ii) combustion wave passing through, and iii) product cooling.…”

Microstructure investigations of Yb- and Bi-doped Mg2Si prepared from metal hydrides for thermoelectric applications

“…In addition to reducing the thermal conductivity in Mg 2 Si, the electrical transport also needs to be adjusted. The optimization of charge carrier concentration can be achieved by doping Mg 2 Si with group 15 th elements, such as Sb or Bi [12][13][14][15]. These dopants have a combined effect on the material, since doping with these heavy elements increases the scattering of heat carrying phonons due to point defect scattering and at the same time add excess electrons, which affects the carrier concentration.…”