The Fundamental Disorder Unit in (Si, P)-(O, N) Networks.

This study presents the synthesis and characterization of oxonitridosilicate phosphates Sr 3 SiP 3 O 2 N 7 , Sr 5 Si 2 P 4 ON 12 , and Sr 16 Si 9 P 9 O 7 N 33 as the first of their kind. These compounds were synthesized under high-temperature (1400 °C) and high-pressure (3 GPa) conditions. A unique structural feature is their common fundamental building unit, a vierer single chain of (Si, P)(O, N) 4 tetrahedra. All tetrahedra comprise substitutional disorder which is why we refer to it as the fundamental disorder unit (FDU). We classified four different FDU motifs, revealing systematic bonding patterns. Including literature known Sr 5 Si 2 P 6 N 16 , three of the four patterns were found in the presented compounds. Common techniques like single-crystal X-ray diffraction (SCXRD), elemental analyses, and 31 P nuclear magnetic resonance (NMR) spectroscopy were utilized for structural analysis. Additionally, low-cost crystallographic calculations (LCC) provided insights into the structure of Sr 16 Si 9 P 9 O 7 N 33 where NMR data were unavailable due to the lack of bulk samples. The optical properties of these compounds, when doped with Eu 2+ , were investigated using photoluminescence excitation (PLE), photoluminescence (PL) measurements, and density functional theory (DFT) calculations. Factors influencing the emission properties, including thermal quenching mechanisms, were discussed. This research reveals the new class of oxonitridosilicate phosphates with unique systematic structural features that offer potential for theoretical studies of luminescence and band gap tuning in insulators.