Reaction and diffusion phenomena in Ag-doped Mg₂Si

The Ag-doped Mg₂Si–based materials are known for unstable thermoelectric behavior; however, the reasons are not sufficiently understood. In this work a range of experiments, analytical tools and calculations was used to unravel some questions related to the reactivity and diffusion properties of the Ag–Mg–Si system, which might contribute to the variations of thermopower. Among these, the most informative appeared quenching and diffusion experiments, calculations of phase evolution by Fact Sage and x-ray tomography of Ag-doped materials produced from powders. - Highlights: • Ag-doped Mg₂Si was produced by combustion synthesis followed by hot pressing. • In-situ and ex-situ doped material contained AgMg intermetallic. • Exclusively grain boundary regions were enriched in silver. • Positive thermopower was repeatedly recorded over 300 °C. • Below 300 °C, thermopower was dependent on thermal history of material.