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

Abstract

We present the synthesis and characterization of oxonitridosilicate phosphates Sr3SiP3O2N7, Sr5Si2P4ON12, and Sr16Si9P9O7N33 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 Sr5Si2P6N16, three of the four patterns were found in the presented compounds. Single‐crystal X‐ray diffraction (SCXRD), elemental analyses, and 31P nuclear magnetic resonance (NMR) spectroscopy were utilized for structural analysis. Additionally, low‐cost crystallographic calculations (LCC) provided insights into the structure of Sr16Si9P9O7N33 where NMR data were unavailable due to the lack of bulk samples. The optical properties of these compounds, when doped with Eu2+, 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.

Super-Tunable LaSi3N5 Structure Type: Insights into the Structure and Luminescence of SrSi2PN5:Eu2+

“… 31 P NMR spectrum of SrSi 2 PN 5 with a signal at −9.7 ppm and a half-width of 3.8 ppm, which confirms the ordered nature of the (Si,P)–N network. Signals of the minor phase are marked by (*) and can be attributed to Sr 3 SiP 3 O 2 N 7 :(NH) 2– …”

“…Theoretically, there is also a fourth combination, in which all tetrahedra have a mixed occupancy of (Si 0.67 ,P 0.33 ), but we were able to rule out this possibility by prior 31 P NMR spectroscopy (Figure ). The 31 P spectrum shows a single narrow signal at −7.9 ppm with a half-width of 3.8 ppm, which indicates the ordered nature of our network, as has been discussed in previous work . The weak additional peaks match well with those of the previously published minor side phase Sr 3 SiP 3 O 2 N 7 :(NH) 2– .…”

“…Since the investigation and differentiation of these elements by X-ray diffraction are often considered insufficient, it must be complemented by other analytical methods. In a previous work, we have already proposed different approaches to distinguish Si 4+ and P 5+ , e.g., by exploiting their characteristic X-ray emissions in scanning transmission electron microscopy in combination with energy-dispersive X-ray spectroscopy at atomic resolution, better known as scanning transmission electron microscopy energy-dispersive X-ray (STEM-EDX) maps. , However, their discrimination is not limited to the interaction with their electron clouds, as we have shown by studying the 31 P solid-state NMR spectra of disordered oxonitridosilicate phosphates (SiPONs), Sr 3 SiP 3 O 2 N 7 and Sr 5 Si 2 P 4 ON 12 . While these methods provide reliable results, in this work, we were interested in further extending the analytical capabilities for this class of compounds by powder neutron diffraction (PND) and adding another method that interacts with the nuclei.…”

“…3,4 However, their discrimination is not limited to the interaction with their electron clouds, as we have shown by studying the 31 P solidstate NMR spectra of disordered oxonitridosilicate phosphates (SiPONs), Sr 3 SiP 3 O 2 N 7 and Sr 5 Si 2 P 4 ON 12 . 2 While these methods provide reliable results, in this work, we were interested in further extending the analytical capabilities for this class of compounds by powder neutron diffraction (PND) and adding another method that interacts with the nuclei. Not as a proof of principle, but due to the fact that we expected better scattering contrasts for Si 4+ /P 5+ and O 2− /N 3− when using neutrons compared to X-rays.…”

“…This chemical similarity is often associated with similar size and electron density, which reduces the X-ray contrast but makes it possible to occupy the same crystallographic sites. Prominent examples of this are the pairings O 2– and N 3– as well as the network-forming cations Si 4+ and P 5+ . , It is no coincidence that these elements make up the main component of the compound presented in this contribution, namely, SrSi 2 PN 5 , a new strontium nitridosilicate phosphate. Since the investigation and differentiation of these elements by X-ray diffraction are often considered insufficient, it must be complemented by other analytical methods.…”