BaCu4/3Si2/3P2 and BaCu2-(x+ y)ZnxSiyP2: Expanding the Semiconducting Landscape in the ThCr2Si2-Type Family

Abstract

ThCr₂Si₂-type layered materials are a large family of compounds with applications ranging from thermoelectricity to magnetism, with the vast majority of the members exhibiting metallic behavior. In this study, we synthesized a new group of materials with Cu-Si and Cu-Zn-Si square nets with the general formula BaCu_1.33Si_0.67P₂ and BaCu_2-(x+y)Zn_xSi_yP₂ (0 ≤ x ≤ 0.9; 0.3 ≤ y ≤ 0.7). Several synthesized compounds are charge-balanced semiconductors, which are rare in the ThCr₂Si₂ family. All the reported compounds crystallize in the ThCr₂Si₂-type tetragonal I4/mmm space group, with Cu/Zn/Si jointly occupying the same 4d crystallographic site. In the Zn-free composition, BaCu_1.33Si_0.67P₂, Ba, and P each occupy a single crystallographic site. The introduction of Zn results in the expansion of the unit cell and splitting the Ba atomic sites along the [001] direction. Such structural displacement of the Ba atoms was confirmed by the heat capacity measurements. Band structure and density-of-states calculations on ordered hypothetical structural models reveal either a small bandgap (∼0.2 eV) or semimetallic band structures. The compounds reported here exhibit high Seebeck coefficients and ultralow thermal conductivity, making them promising candidates for the development of thermoelectric materials.