High Temperature Thermoelectric Properties of the Solid-Solution Zintl Phase Eu₁₁Cd_6–xZn_xSb₁₂

Solid-solution Zintl compounds with the formula Eu 11 Cd 6– x Zn x Sb 12 have been synthesized from the elements as single crystals using a tin flux according to the stoichiometry Eu:Cd:Zn:Sb:Sn of 11:6– x p: x p:12:30 with x p = 0, 1, 2, 3, 4, 5, and 6, where x p is the preparative amount of Zn employed in the reaction. The crystal structures and the compositions were established by single-crystal as well as powder X-ray diffraction and wavelength-dispersive X-ray analysis measurements. The title solid-solution Zintl compounds crystallize isostructurally in the centrosymmetric monoclinic space group C 2/ m (No. 12, Z = 2) as the Sr 11 Cd 6 Sb 12 structure type (Pearson symbol mC 58). There is a miscibility gap at 3 ≤ x p ≤ 4 where the major product crystallizes in a disordered structure related to the Ca 9 Mn 4 Bi 9 structure type; otherwise, for all other compositions, the Sr 11 Cd 6 Sb 12 structure is the majority phase. Eu 11 Cd 6 Sb 12 shows lower lattice thermal conductivity relative to Eu 11 Zn 6 Sb 12 consistent with its higher mean atomic weight, and as anticipated, the solid-solution samples of Eu 11 Cd 6– x Zn x Sb 12 have effectively reduced lattice thermal conductivities relative to the end member compounds. Eu 11.0(1) Cd 4.5(2) Zn 1.5(2) Sb 12.0(1) exhibits the highest zT value of >0.5 at around 800 K which is twice as large as the end member compounds.