High Temperature Thermoelectric Properties of the Solid-Solution Zintl Phase Eu₁₁Cd_{6- x}Zn_xSb₁₂

Solid-solution Zintl compounds with the formula Eu₁₁Cd_6-xZn_xSb₁₂ 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 Sr₁₁Cd₆Sb₁₂ structure type (Pearson symbol mC58). There is a miscibility gap at 3 x_p 4 where the major product crystallizes in a disordered structure related to the Ca₉Mn₄Bi₉ structure type; otherwise, for all other compositions, the Sr₁₁Cd₆Sb₁₂ structure is the majority phase. Eu₁₁Cd₆Sb₁₂ shows lower lattice thermal conductivity relative to Eu₁₁Zn₆Sb₁₂ consistent with its higher mean atomic weight, and as anticipated, the solid-solution samples of Eu₁₁Cd_6-xZn_xSb₁₂ 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.