Corrosion behavior of thermoelectric clathrates alpha- and beta-Eu8Ga16-xGe30+x in air

The corrosion of thermoelectric clathrates alpha- and beta-Eu8Ga16-xGe30+x is studied under static air (DSC/TG) up to 650 °C. Oxidation product layers with thicknesses of 10.5 µm (alpha-Eu8Ga16-xGe30+x) and 4.5 µm (beta-Eu8Ga16-xGe30+x) are formed. The oxidation begins at 360 and 380 °C, respectively. XRD pattern of the beta-Eu8Ga16-xGe30+x oxidized layer shows Ge and four Eu2O3 reflections; while alpha-Eu8Ga16-xGe30+x data (sample crushed and grinded) shows alpha-Eu8Ga16-xGe30+x reflections (majority phase), two EuGa2±xGe4minus-or-plus signx strongest reflections and Ge (minority phases). These results indicate the amount of oxides is very small or they are amorphous. High temperature powder XRD measurements on alpha-Eu8Ga16-xGe30+x under air confirm the oxidation onset temperature determined in DSC studies.