Structure transition and thermoelectric properties related to AZn(1-x)/2CuxSb (A = Ca, Eu, Sr; 0

Abstract

The copper-containing antimony compounds with the general formulae ACuSb (A = Ca, Sr, Eu) were reported to adopt the ZrBeSi structure type, which feature a planar CuSb layer composed of honeycomb-like Cu3Sb3 rings. The Zn-containing analogues can crystallize in such a structure type too, but with ∼50% occupancy at the transition metal site and a disordered A2ZnSb2 structure. Interestingly, phase transition was proven from the ZrBeSi type to the LiGaGe type when Cu and Zn were both incorporated in the anionic structure, which led to the discovery of a series of new Cu/Zn-mixed Zintl phases, CaZn0.36(1)Cu0.28(1)Sb, EuZn0.25(3)Cu0.50(3)Sb and SrZn0.17(3)Cu0.65(3)Sb. The crystal structures of these novel phases were accurately determined through the single-crystal X-ray diffraction method, which indicated the P63mc (no. 186) space group with cell parameters: a = 4.5234(3)/4.5705(6)/4.5863(9) Å and c = 7.9562(10)/8.431(2)/8.698(3) Å for the Ca-, Sr- and Eu-containing compounds, respectively. Thermoelectric properties were systematically investigated by materials AZn0.25Cu0.5Sb (A = Ca, Sr, Eu) with nominally the same compositions. Electronic band structure calculations were performed by various models constructed based on the Sr compounds, which suggested significant convergence of the valence bands with structure transition from the ZrBeSi type to the LiGaGe type.