Tetra-Face-Capped Octahedra in a Tetrahedra Network - Structure Determination and Scanning Transmission Electron Microscopy of SrAl5 P4 N10 O2 F3.

Abstract

Tetrahedra-based nitridophosphates show a rich structural chemistry, which can be further extended by incorporating cations in higher coordinated positions, for example, in octahedral voids or by substituting the nitrogen atoms in the network with other anions. Following this approach, SrAl5 P4 N10 O2 F3 was synthesized at high-temperature and high-pressure conditions using a multianvil press (1400 °C, 5 GPa) starting from Sr(N3 )2 , c-PON, P3 N5 , AlN, and NH4 F. SrAl5 P4 N10 O2 F3 crystallizes in space group with a=11.1685(2) and c=7.84850(10) Å. Atomic-resolution EDX mapping with scanning transmission electron microscopy (STEM) indicates atom assignments, which are further corroborated by bond-valence sum (BVS) calculations. Ten Al3+ -centered octahedra form a highly condensed tetra-face-capped octahedra-based unit that is a novel structure motif in network compounds. A network of vertex-sharing PN4 tetrahedra and chains of face-sharing Sr2+ -centered cuboctahedra complement the structure. Eu2+ -doped SrAl5 P4 N10 O2 F3 shows blue emission (λem= 469 nm, fwhm=98 nm; 4504 cm-1 ) when irradiated with UV light.