High temperature thermoelectric properties of the solid-solution zintl phase Eu₁₁Cd6-xZnxSb

Solid-solution Zintl compounds with the formulaEu₁₁Cd6-xZnxSb₁₂ 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–xp:xp:12:30 with xp = 0, 1, 2, 3, 4, 5, and 6, where xp 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 ≤ xp ≤ 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 Eu₁₁Cd6–xZnxSb₁₂ have effectively reduced lattice thermal conductivities relative to the end member compounds. Eu₁₁̣̣₀(1)Cd₄̣̣₅(2)Zn₁̣̣₅(2)Sb₁₂̣̣₀(1) exhibits the highest zT value of >0.5 at around 800 K which is twice as large as the end member compounds.