Systematic analysis of the interplay between synthesis route, microstructure and thermoelectric performance in p-type Mg 2 Si 0.2 Sn 0.8 H. Kamila a *, G. K. Goyal c *, A. Sankhla a , P. Ponnusamy a , E. Mueller a,b , T. Dasgupta c and J. de Boor a a Institute of Materials Research, German Aerospace Center (DLR), 51147 Koeln, Germany b Institute of Inorganic and Analytical Chemistry, Justus Liebig University Giessen, 35392 Giessen, Germany c Department of Metallurgical Engineering and Materials Science, Indian Institute of Technology Bombay, Mumbai 400 076, India Corresponding Authors: hasbuna.kamila@dlr.de, Johannes.deBoor@dlr.de Abstract For thermoelectric materials, the synthesis route is – besides composition – the crucial factor governing the thermoelectric transport properties and hence the performance of the material. Here we present a systematic analysis of the influence of the synthesis technique on microstructure and thermoelectric transport properties in Li doped Mg 2 Si 0.2 Sn 0.8 . The samples were prepared using two wide-spread, but quite different synthesis methods: high energy ball milling and induction melting. Microstructural analysis (scanning electron microscopy, X-ray diffraction) reveals that ball milled samples are more homogenous than induction melted ones, which exhibit some Si-rich Mg 2 (Si,Sn) and MgO as secondary phases. On a first glance the thermoelectric properties are qualitatively similar with  max ≈ 0.4 for both routes. However, a systematic analysis of the high temperature transport data in the framework of a single parabolic band model points out that the induction melted samples have a systematically reduced mobility and increased lattice thermal conductivity which can be tied to the differences in the microstructure. The reduced mobility can be attributed to a further carrier scattering mechanism for the induction melted samples in addition to the acoustic phonon and alloy scattering that are observed for both synthesis routes while increased lattice thermal conductivity is due to the larger grain size and presence of secondary phases. In consequence this leads to significantly enhanced thermoelectric transport properties for ball milled samples (effective material parameter  is ~20% larger) and a predicted relative difference in device efficiency of more than 10%. Key words: Ball milling; Induction melting; Single Parabolic Band Model; Thermoelectrics; Thermoelectric transport properties analysis