Tunable β-FeSi2 – Si1-yGey nanocomposites by a novel React/Transform Spark Plasma Sintering approach for thermoelectric applications. (March 2018)

• Record Type: Journal Article
• Authors: Liu, Naiming; Jensen, Wade A.; Zebarjadi, Mona; Floro, Jerrold A.
• Is Part Of: Materials today physics. Volume 4(2017)
• Page Start: 19
• Page End: 27
• Publication Date: 2018-03
• Subjects: Thermoelectric -- β-FeSi2 -- Nanocomposite -- Thermal conductivity -- React/Transform Spark Plasma Sintering; Materials science -- Periodicals; Physics -- Periodicals; Electronic journals; 530.41
• DOI: 10.1016/j.mtphys.2018.02.004
• Languages: English
• ISSNs: 2542-5293

Abstract

Abstract: We developed a novel React/Transform Spark Plasma Sintering approach for nanocomposite synthesis, providing accelerated phase transformation and selective alloying. We synthesized compositionally tunable SiGe alloy particles, embedded within a β-FeSi2 matrix, both with nanoscale grain size. This is achieved simply by adding a few atomic percent of Ge into pre-cast α-FeSi2+δ via light ball-milling, followed by two-step spark plasma sintering. This processing approach is much more efficient than conventional β-FeSi2 synthesis methods, due to significantly accelerated eutectoid decomposition, α-FeSi2+δ → β-FeSi2 + Si, followed by a facile Ge incorporation into eutectoid Si, without mechanical alloying and post-annealing. Increasing the Ge content of the nanocomposite drives significant reductions in the overall thermal conductivity. We analyzed the temperature dependence of thermal conductivity of the nanocomposite system by including phonon-phonon scattering, alloying scattering (in SiGe) and boundary scattering (size effect) in each phase, and then average over the two phases. The modeling indicates that the reduction of κ L ( T ) results from both the nanostructuring and Ge alloying achieved by the processing route. Our approach offers a promising means for synthesizing self-assembled nanocomposite materials for thermoelectric applications. Graphical abstract: Highlights: Tunable β-FeSi2 – Si1-y Gey nanocomposites were synthesized by an efficient React/Transform SPS process without mechanical alloying and post annealing. Accelerated Fe-Si eutectoid phase transformation and facile Si-Ge selective alloying were achieved by SPS conditions. Nanostructuring and Ge incorporation by this process effectively suppressed the overall thermal conductivity.