Prospective p-type magnesium-silicon compounds have been produced from mixed and sintered Mg2Si, Mg2Sr or Mg2Ba powders. The synthesis was carried out through the spark plasma sintering (SPS) process at 1123 K for 10 min at 50 MPa. p-Type thermoelectric performance was observed for samples prepared from sintered powder at nominal compositions (Mg2Si)0.7(Mg2Sr)0.3 and (Mg 2Si)0.7(Mg2Ba)0.3. The maximum dimensionless figure of merit, ZT, of the former sample reached 0.24 at 700 K. The crystal structures and chemical contents were carefully elucidated by powder and single-crystal x-ray diffraction (XRD) measurements, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) with the use of energy-dispersive x-ray spectroscopy (EDS). The SPS samples consisted of two new unknown phases. Based on the single-crystal XRD data, the crystal structures of two different A(Sr or Ba)-Mg-Si crystals are successfully determined. The two structures are hexagonal P63/m-type A2Mg 12Si7 and P6̄2m (no. 189)-type A2Mg 4Si3. The two structures consist of three-dimensionally interconnecting MgSi4 tetrahedron networks and alkaline-earth ion columns aligned parallel to the 4.3-Å axes. Both phases have identical [(A2+, Mg2+)]2[Si4-]-type chemical formulae, being identified as a kind of Zintl phase.
- Alkaline-earth metal
- p-type magnesium silicon semiconductor
- single-crystal structure refinement
- Zintl phase