Seebeck coefficient variations of α-MgAgSb in crystalline Mg-Ag-Sb thin films

α-MgAgSb is a thermoelectric material exhibiting promising performances at room temperature, and thus, attracting wide attention for low-grade heat conversion. However, large variations of its Seebeck coefficient were reported by different authors. These variations were recently suggested to be related to the possible variation of α-MgAgSb stoichiometry. In this work, the Seebeck coefficient of α-MgAgSb was measured in Mg-Ag-Sb thin films deposited by magnetron sputtering and crystallized in situ or ex situ, considering the film microstructure as well as the experimental Seebeck coefficient of the additional secondary phases present in the films. Mg-Ag-Sb films with two different compositions were investigated: the Sb-rich solid solution MgAgSb1.12 and the Ag-poor solid solution MgAg0.17Sb. The Seebeck coefficient of α-MgAgSb is found to be independent of the phase proportions in the Mg-Ag-Sb films. However, α-MgAgSb displays different Seebeck coefficients in the films MgAgSb1.12 and MgAg0.17Sb, a lack of Ag leading to a significant decrease of the α-MgAgSb Seebeck coefficient. These results support α-MgAgSb stoichiometry variations leading to significant variations of the Seebeck coefficient. The present work gives new insights about α-MgAgSb thin films and provides a solid support for future improvement.