Germanide clathrates resistance to incorporation of trivalent rare earths

Abstract We performed elemental analysis and transport measurements (resistivity and Seebeck coefficient) in single crystal clathrate samples with starting compositions Ba 8 Ga y M z Ge 46 - y - z (M = Au, Ag) and Ba 8 - x R x Ga y Ag z Ge 46 - y - z (R = La, Ce, Eu). Electron-probe microanalysis (EPMA) indicated that no trivalent rare earths (La and Ce) were incorporated into the germanium clathrates, neither with gold or silver as acceptors; the former was included in large amounts, in contrast to the latter, which nonetheless allowed the inclusion of small amounts of Eu. Transport measurements did not show significant improvement in the thermoelectric properties in singlecrytalline Au-clathrate samples compared to their known polycrystalline correspondents. The Ag-clathrates showed very similar thermoelectric properties with or without the inclusion of Eu.