High Temperature Thermoelectric Properties of the Solid-Solution Zintl Phase Eu_(11)Cd_(6–x)Zn_xSb_(12)

Abstract

Solid-solution Zintl compounds with the formula Eu_(11)Cd_(6–x)Zn_xSb_(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_6Sb_(12) 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 Ca_9Mn_4Bi_9 structure type; otherwise, for all other compositions, the Sr_(11)Cd_6Sb_(12) structure is the majority phase. Eu_(11)Cd_6Sb_(12) shows lower lattice thermal conductivity relative to Eu_(11)Zn_6Sb_(12) consistent with its higher mean atomic weight, and as anticipated, the solid-solution samples of Eu_(11)Cd_(6–x)Zn_xSb_(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.

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