High-temperature thermoelectric studies of A11Sb10 (A=Yb, Ca)

Large samples (6–8 g) of Yb11Sb10 and Ca11Sb10 have been synthesized using a high-temperature (1275–1375 K) flux method. These compounds are isostructural to Ho11Ge10, crystallizing in the body-centered, tetragonal unit cell, space group I4/mmm, with Z=4. The structure consists of antimony dumbbells and squares, reminiscent of Zn4Sb3 and filled Skutterudite (e.g., LaFe4Sb12) structures. In addition, these structures can be considered Zintl compounds; valence precise semiconductors with ionic contributions to the bonding. Differential scanning calorimetry (DSC), thermogravimetry (TG), resistivity (ρ), Seebeck coefficient (α), thermal conductivity (κ), and thermoelectric figure of merit (zT) from room temperature to at minimum 975 K are presented for A11Sb10 (A=Yb, Ca). DSC/TG were measured to 1400 K and reveal the stability of these compounds to ∼1200 K. Both A11Sb10 (A=Yb, Ca) materials exhibit remarkably low lattice thermal conductivity (∼10 mW/cm K for both Yb11Sb10 and Ca11Sb10) that can be attributed to the complex crystal structure. Yb11Sb10 is a poor metal with relatively low resistivity (1.4 mΩ cm at 300 K), while Ca11Sb10 is a semiconductor suggesting that a gradual metal–insulator transition may be possible from a Ca11−xYbxSb10 solid solution. The low values and the temperature dependence of the Seebeck coefficients for both compounds suggest that bipolar conduction produces a compensated Seebeck coefficient and consequently a low zT.

Large samples (6–8 g) of Yb11Sb10 and Ca11Sb10 have been synthesized from a Sn-flux method. Thermoelectric measurements from room temperature to 1075 K have been obtained. Both A11Sb10 (A=Yb, Ca) materials exhibit remarkably low lattice thermal conductivity (∼10 mW/cm K for both Yb11Sb10 and Ca11Sb10) that can be attributed to the complex crystal structure.Figure optionsDownload as PowerPoint slide