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 Ag1.7(1)Ge1.0(1)P14 and Ag1.4(1)Sn1.0(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 Pnma(0β0)s00 (No. 62.1.9.4). Ag1.7(1)Ge1.0(1)P14 (refined composition Ag2.2(1)Ge1.3(1)P18.7(1)) with the cell parameters a = 12.986(1) Å, b = 3.2648(4) Å, c = 10.841(1) Å, and a modulation wave vector q = (0, 0.39(1), 0), and Ag1.4(1)Sn1.0(1)P14 (refined as Ag1.9(1)Sn1.3(1)P18.7(1)) with a = 13.014(1) Å, b = 3.2602(4) Å, c = 10.905(1) Å, and q = (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 Ag1.4(1)Sn1.0(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 Ag1.7(1)Ge1.0(1)P14 (0.2 S/cm).