Layered silicates are a very versatile class of materials with high importance to humanity. The new nitridophosphates MP6N11 (M=Al, In), synthesized from MCl3, P3N5 and NH4N3 in a high‐pressure high‐temperature reaction at 1100 °C and 8 GPa, show a mica‐like layer setup and feature rare nitrogen coordination motifs. The crystal structure of AlP6N11 was elucidated from synchrotron single‐crystal diffraction data (space group Cm (no. 8), a=4.9354(10), b=8.1608(16), c=9.0401(18) Å, β=98.63(3)°), enabling Rietveld refinement of isotypic InP6N11. It is built up from layers of PN4 tetrahedra, PN5 trigonal bipyramids and MN6 octahedra. PN5 trigonal bipyramids have been reported only once and MN6 octahedra are sparsely found in the literature. AlP6N11 was further characterized by energy‐dispersive X‐ray (EDX), IR and NMR spectroscopy. Despite the vast amount of known layered silicates, there is no isostructural compound to MP6N11 as yet.
Layered silicates are a very versatile class of materials with high importance to humanity. The new nitridophosphates MP6N11 (M=Al, In), synthesized from MCl3, P3N5 and NH4N3 in a high‐pressure high‐temperature reaction at 1100 °C and 8 GPa, show a mica‐like layer setup and feature rare nitrogen coordination motifs. The crystal structure of AlP6N11 was elucidated from synchrotron single‐crystal diffraction data (space group Cm (no. 8), a=4.9354(10), b=8.1608(16), c=9.0401(18) Å, β=98.63(3)°), enabling Rietveld refinement of isotypic InP6N11. It is built up from layers of PN4 tetrahedra, PN5 trigonal bipyramids and MN6 octahedra. PN5 trigonal bipyramids have been reported only once and MN6 octahedra are sparsely found in the literature. AlP6N11 was further characterized by energy‐dispersive X‐ray (EDX), IR and NMR spectroscopy. Despite the vast amount of known layered silicates, there is no isostructural compound to MP6N11 as yet.
Tetrahedra‐based nitridophosphates show a rich structural chemistry, which can be further extended by incorporating cations in higher coordinated positions, e.g., in octahedral voids or by substituting the nitrogen atoms in the network with other anions. Following this approach, SrAl5P4N10O2F3 was synthesized at high‐temperature and high‐pressure conditions using a multianvil press (1400 °C, 5 GPa) starting from Sr(N3)2, c‐PON, P3N5, AlN, and NH4F. SrAl5P4N10O2F3 crystallizes in space group I[[EQUATION]]m2 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 SrAl5P4N10O2F3 shows blue emission (λem = 469 nm, fwhm = 98 nm; 4504 cm–1) when irradiated with UV light.
RbGe 7 As 15 and CsGe 7 As 15 have been synthesized and their structures were determined by single-crystal X-ray diffraction and high-angle annular dark-field scanning transmission electron microscopy/energy-dispersive X-ray spectroscopy. They crystallize with a cubic sodalite-type structure in the space group I4̅ 3m isotypic to BaGe 8 As 14 . Rubidium and cesium are highly coordinated by 16 arsenic or germanium atoms and fit better into the sodalite cage due to their bigger ionic radii compared to barium, which is displaced from the center. The compounds are narrow-band p-type semiconductors with electrical conductivities of 1.2−3 × 10 4 S/m at 300 K and carrier densities of 1−2 × 10 20 cm −1 . First-principles DFT calculations give clear evidence of ultralow lattice thermal conductivity around 0.5 Wm −1 K −1 in BaGe 8 As 14 due to the position disorder of the barium atoms and the anharmonicity of its thermal movement. Frozen phonon calculations and heat capacity data indicate that rattling probably decreases the lattice thermal conductivity of BaGe 8 As 14 even further. These effects are chemically switched off in RbGa 7 As 15 with a parabolic potential and no signs of rattling, leading to a four times higher lattice thermal conductivity. All calculated transport properties agree with the measured data, and their combination predicts a thermoelectric efficiency ZT up to 2.7 for BaGe 8 As 14 , reaching the value of current record materials.
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