A₅Sn₂As₆ (A = Sr, Eu). Synthesis, Crystal and Electronic Structure, and Thermoelectric Properties

Two new ternary Zintl phases, Sr₅Sn₂As₆ and Eu₅Sn₂As₆, have been synthesized, and their structures have been accurately determined through single-crystal X-ray diffraction. Both compounds crystallize in orthorhombic space group <i>Pbam</i> (No. 55, <i>Z</i> = 2) with cell parameters of <i>a</i> = 12.482(3)/12.281(5) Å, <i>b</i> = 14.137(3)/13.941(5) Å, and <i>c</i> = 4.2440(10)/4.2029(16) Å for Sr₅Sn₂As₆ (R1 = 0.0341; wR2 = 0.0628) and Eu₅Sn₂As₆ (R1 = 0.0324; wR2 = 0.0766), respectively. Their structure belongs to the Sr₅Sn₂P₆ type, which can be closely related to the Ca₅Ga₂As₆ type. Electronic band structure calculations based on the density functional theory reveal an interesting electronic effect in the structure formation of these two types of Zintl phases, which substantially affect their corresponding electronic band structure. Related studies on the thermal stability, magnetism, and thermoelectric properties of Eu₅Sn₂As₆ are presented as well