Enhanced Thermoelectric Performance in Mg2Si by Functionalized Co‐Doping

• Published in: Physica status solidi. A, Applications and materials science Applications and materials science, 2018-11, Vol.215 (21), p.n/a
• Main Authors: Mitra, Kunal, Goyal, Gagan K., Rathore, Ekashmi, Biswas, Kanishka, Vitta, Satish, Mahapatra, Suddhasatta, Dasgupta, Titas
• Format: Article
• Language: English
• Subjects: Bismuth; Carrier density; Carrier mobility; Composition; Current carriers; Density of states; Dopants; Figure of merit; Grain boundaries; Induction melting; Intermetallic compounds; Magnesium compounds; Magnesium oxide; magnesium silicide; Metal silicides; Microstructure; Scanning electron microscopy; single parabolic band model; Superconductors (materials); Temperature dependence; Thermal conductivity; thermoelectric; Thermoelectricity; X-ray diffraction
• ISSN: 1862-6300; 1862-6319
• DOI: 10.1002/pssa.201700829

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 (mD*), 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 mD* 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, κL. Functionalized co‐doping approach is found to be effective in improving the thermoelectric performance in magnesium silicide. The individual dopants Se and Al are found to enhance the density of states effective mass (mD*) and mobility μ respectively while the more traditional dopant Bi is found to be effective in reducing the lattice thermal conductivity as it populates the grain boundaries. All these effects combined, yields around 20% higher ZTeng. Multiple doping with individual dopants providing specific increments in ZT can be a way forward in increasing thermoelectric performance of different material systems.