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

摘要

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 similar to 50% occupancy at the transition metal site and a disordered A(2)ZnSb(2) 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, CaZn0.360(1)-Cu0.28(1)Sb, EuZn0.25(3)Cu0.50(3)Sb and SrZn0.12(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 P6(3)mc (no. 186) space group with cell parameters: a = 4.5234(3)/4.5705(6)/4.5863(9) angstrom and c = 7.9562(10)/8.431(2)/8.698(3) angstrom for the Ca-, Sr- and Eu-containing compounds, respectively. Thermoelectric properties were systematically investigated by materials AZn(0.25)Cu(0.5)Sb (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. (C) 2019 Elsevier B.V. All rights reserved.