Low-Dimensional Semiconducting Silver (Germanium, Tin) Polyphosphides – Incommensurately Modulated Derivates of the HgPbP₁₄ Structure Type

Semiconductors with one-dimensional (1D) substructures are promising for next-generation optical and electronic devices due to their directional transport and flexibility. Representatives of this class include HgPbP₁₄-type materials. This study investigates the related semiconductors Ag_1.7(1)Ge_1.0(1)P₁₄ and Ag_1.4(1)Sn_1.0(1)P₁₄. Single-crystal X-ray diffraction indicates that their structure is unconventional due to its incommensurate modulation. Both compounds crystallize orthorhombically in the (3 + 1)D superspace group <i>Pnma</i>(0<i>β</i>0)<i>s</i>00 (No. 62.1.9.4). Ag_1.7(1)Ge_1.0(1)P₁₄ (refined composition Ag_2.2(1)Ge_1.3(1)P_18.7(1)) with the cell parameters <i>a</i> = 12.986(1) Å, <i>b</i> = 3.2648(4) Å, <i>c</i> = 10.841(1) Å, and a modulation wave vector <i>q</i> = (0, 0.39(1), 0), and Ag_1.4(1)Sn_1.0(1)P₁₄ (refined as Ag_1.9(1)Sn_1.3(1)P_18.7(1)) with <i>a</i> = 13.014(1) Å, <i>b</i> = 3.2602(4) Å, <i>c</i> = 10.905(1) Å, and <i>q</i> = (0, 0.42(1), 0) were investigated. Three structural models were generated, differing in modulation functions, site occupancies, and the split of one atomic position. Depending on the occupancy, the structure can be derived from Cu₂P₂₀, AgP₁₅, or HgPbP₁₄ -type materials. ¹¹⁹Sn Mössbauer spectroscopy confirms the +II oxidation state of tin in Ag_1.4(1)Sn_1.0(1)P₁₄. Additional characterization was performed by scanning electron microscopy with energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, angle-dependent Raman spectroscopy, and photoluminescence measurements. Single-crystal conductivity measurements revealed semiconducting behavior of Ag_1.7(1)Ge_1.0(1)P₁₄ (0.2 S/cm).