Metallic properties of Ba2Cu3P4 and BaCu2Pn2 (Pn=As, Sb)

We report the synthesis of ternary barium copper pnictides, Ba2Cu3P4 and BaCu2Pn2 (Pn=As, Sb), and their structural, magnetic, and transport properties. They all crystallize in different structures shown by X-ray diffraction, although their structures reveal close relations. The body-centered tetragonal BaCu2As2 adopts ThCr2Si2-type (I4/mmm) structure, whereas Ba2Cu3P4 is a copper-deficient derivative of this phase, crystallizing in the body-centered orthorhombic space group, Ibam. There are two polymorphs of BaCu2Sb2: α-BaCu2Sb2 that adopts CaBe2Ge2-type structure; β-BaCu2Sb2 that is a 2:1 combination of CaBe2Ge2- and ThCr2Si2-type structural segments. All phases are metallic and non-magnetic. The room temperature thermal conductivity for polycrystalline BaCu2As2 is ≈ 2 W/(m K) and the Seebeck coefficient is ≈ 15 μV/K, which result in a small (≈0.03) thermoelectric figure of merit.