Multicationic Tetrahedra Networks: Alkaline-Earth-Centered Polyhedra and Non-Condensed AlN6-Octahedra in the Imidonitridophosphates AE2AlP8N15(NH) (AE=Ca, Sr, Ba)

A series of isostructural imidonitridophosphates AE2AlP8N15(NH) (AE=Ca, Sr, Ba) was synthesized at high-pressure/high-temperature conditions (1400 °C and 5-9 GPa) from alkaline-earth metal nitrides or azides Ca3N2/Sr(N3)2/Ba(N3)2 and the binary nitrides AlN and P3N5. NH4F served as a hydrogen source and mineralizing agent. The crystal structures were determined by single-crystal X-ray diffraction and feature a three-dimensional network of vertex-sharing PN4-tetrahedra forming diverse-sized rings that are occupied by aluminum and alkaline earth ions. These structures represent another example of nitridophosphate-based networks that simultaneously incorporate AlN6-octahedra and alkaline-earth-centered polyhedra, with aluminum not participating in the tetrahedra network. They differ from previously reported ones by incorporating non-condensed octahedra instead of strongly condensed octahedra units and contribute to the diversity of multicationic nitridophosphate network structures. The results are supported by atomic resolution EDX mapping, solid-state NMR and FTIR measurements. Eu2+-doped samples show strong luminescence with narrow emissions in the range of green to blue under UV excitation, marking another instance of Eu2+-luminescence within imidonitridophosphates.

High-Pressure Synthesis of Sc5 P12 N23 O3 and Ti5 P12 N24 O2 by Activation of the Binary Nitrides ScN and TiN with NH4 F

Multinary transition metal nitrides and oxonitrides are a versatile and intriguing class of compounds. However, they have been investigated far less than pure oxides. The compounds Sc5 P12 N23 O3 and Ti5 P12 N24 O2 have now been synthesized from the binary nitrides ScN and TiN, respectively, by following a high-pressure high-temperature approach at 8 GPa and 1400 °C. NH4 F acts as a mineralizing agent that supports product formation and crystallization. The starting materials ScN and TiN are seemingly an uncommon choice because of their chemical inertness but, nevertheless, react under these conditions. Sc5 P12 N23 O3 and Ti5 P12 N24 O2 crystallize isotypically with Ti5 B12 O26 , consisting of solely vertex-sharing P(O/N)4 tetrahedra forming two independent interpenetrating diamond-like nets that host TM(O/N)6 (TM=Sc, Ti) octahedra. Ti5 P12 N24 O2 is a mixed-valence compound and shows ordering of Ti3+ and Ti4+ ions.

Nitridophosphate-Based Ultra-Narrow-Band Blue-Emitters: Luminescence Properties of AEP8 N14 :Eu2+ (AE=Ca, Sr, Ba)

The nitridophosphates AEP8 N14 (AE=Ca, Sr, Ba) were synthesized at 4-5 GPa and 1050-1150 °C applying a 1000 t press with multianvil apparatus, following the azide route. The crystal structures of CaP8 N14 and SrP8 N14 are isotypic. The space group Cmcm was confirmed by powder X-ray diffraction. The structure of BaP8 N14 (space group Amm2) was elucidated by a combination of transmission electron microscopy and diffraction of microfocused synchrotron radiation. Phase purity was confirmed by Rietveld refinement. IR spectra are consistent with the structure models and the chemical compositions were confirmed by X-ray spectroscopy. Luminescence properties of Eu2+ -doped samples were investigated upon excitation with UV to blue light. CaP8 N14 (λem =470 nm; fwhm=1380 cm-1 ) and SrP8 N14 (λem =440 nm; fwhm=1350 cm-1 ) can be classified as the first ultra-narrow-band blue-emitting Eu2+ -doped nitridophosphates. BaP8 N14 shows a notably broader blue emission (λem =417/457 nm; fwhm=2075/3550 cm-1 ).

Nitridophosphates: A Success Story of Nitride Synthesis

Nitridophosphates and phosphorus nitrides are thoroughly investigated classes of nitrides. During thirty years of research, the methods for their synthesis evolved from the condensation of molecular precursors at moderate temperatures and ambient pressures to state-of-the-art high-pressure and high-temperature processes. Landmark breakthroughs made in recent years led to a comprehension-based proficiency in nitridophosphate synthesis that is illustrated by the large compositional and structural diversity of the nitridophosphates known today. Herein, we review the advances made in synthesis with regard to the prevalent problem of nitride synthesis: the susceptibility of nitride ions to oxidation.

Rivalry under Pressure: The Coexistence of Ambient-Pressure Motifs and Close-Packing in Silicon Phosphorus Nitride Imide SiP2 N4 NH

Non-metal nitrides such as BN, Si₃ N₄ , and P₃ N₅ meet numerous demands on high-performance materials, and their high-pressure polymorphs exhibit outstanding mechanical properties. Herein, we present the silicon phosphorus nitride imide SiP₂ N₄ NH featuring sixfold coordinated Si. Using the multi-anvil technique, SiP₂ N₄ NH was obtained by high-pressure high-temperature synthesis at 8 GPa and 1100 °C with in situ formed HCl acting as a mineralizer. Its structure was elucidated by a combination of single-crystal X-ray diffraction and solid-state NMR measurements. Moreover, SiP₂ N₄ NH was characterized by energy-dispersive X-ray spectroscopy and (temperature-dependent) powder X-ray diffraction. The highly condensed Si/P/N framework features PN₄ tetrahedra as well as the rare motif of SiN₆ octahedra, and is discussed in the context of ambient-pressure motifs competing with close-packing of nitride anions, representing a missing link in the high-pressure chemistry of non-metal nitrides.

SrH4 P6 N12 and SrP8 N14 : Insights into the Condensation Mechanism of Nitridophosphates under High Pressure

The (imido)nitridophosphates SrH₄ P₆ N₁₂ and SrP₈ N₁₄ were synthesized as colorless crystals by high-pressure/high-temperature reactions using the multianvil technique (5 GPa, ca. 1075 °C). Stoichiometric amounts of Sr(N₃ )_2, P₃ N₅ , and amorphous HPN₂ were used as starting materials. Whereas the crystal structure of SrH₄ P₆ N₁₂ was solved and refined from single-crystal X-ray diffraction data and confirmed by Rietveld refinement, the structure of SrP₈ N₁₄ was determined from powder diffraction data. In order to confirm the structures, ¹ H and ³¹ P solid-state NMR spectroscopy and FTIR spectroscopy were carried out. The chemical composition was confirmed with EDX measurements. Both compounds show unprecedented layered network structure types, built up from all-side vertex-sharing PN₄ tetrahedra which are structurally related. The structural comparison of both compounds gives first insights into the hitherto unknown condensation mechanism of nitridophosphates under high pressure.

SrP3 N5 NH: A Framework-Type Imidonitridophosphate Featuring Structure-Directing Hydrogen Bonds

Nitridophosphates and imidonitridophosphates show intriguing structural diversity, including unprecedented structure types. Highly condensed strontium imidonitridophosphate SrP₃ N₅ NH has been synthesized at 8 GPa and 1100 °C using a high-pressure high-temperature approach starting from stoichiometric amounts of Sr(N₃ )₂ , P₃ N₅ and NH₄ Cl. Herein, NH₄ Cl was used as a hydrogen source and as a precursor for in situ formation of SrCl₂ , which acts as mineralizer and facilitates growth of single-crystals with a diameter of ≤30 μm. SrP₃ N₅ NH (P2₁ /c (no. 14), a=5.01774(2), b=8.16912(4), c=12.70193(5) Å, β=101.7848(3)°, Z=4) adopts an unprecedented network structure, represented by the point symbol (3.4.5.6.7² )(3.4.5.7² .8)(3.6.7³ .8). This unique three nodal P/N(H) network is stabilized by moderately strong hydrogen bonds causing a structure-directing effect, which has not yet been reported for imidonitridophosphates.

Li+ Ion Conductors with Adamantane-Type Nitridophosphate Anions β-Li10 P4 N10 and Li13 P4 N10 X3 with X=Cl, Br

β-Li₁₀ P₄ N₁₀ and Li₁₃ P₄ N₁₀ X₃ with X=Cl, Br have been synthesized from mixtures of P₃ N₅ , Li₃ N, LiX, LiPN₂ , and Li₇ PN₄ at temperatures below 850 °C. β-Li₁₀ P₄ N₁₀ is the low-temperature polymorph of α-Li₁₀ P₄ N₁₀ and crystallizes in the trigonal space group R3. It is made up of non-condensed [P₄ N₁₀ ]^10- T2 supertetrahedra, which are arranged in sphalerite-analogous packing. Li₁₃ P₄ N₁₀ X₃ (X=Cl, Br) crystallizes in the cubic space group Fm3‾m . Both isomorphic compounds comprise adamantane-type [P₄ N₁₀ ]^10- , Li⁺ ions, and halides, which form octahedra. These octahedra build up a face-centered cubic packing, whose tetrahedral voids are occupied by the [P₄ N₁₀ ]^10- ions. The crystal structures have been elucidated from X-ray powder diffraction data and corroborated by EDX measurements, solid-state NMR, and FTIR spectroscopy. Furthermore, we have examined the phase transition between α- and β-Li₁₀ P₄ N₁₀ . To confirm the ionic character, the migration pathways of the Li⁺ ions have been evaluated and the ion conductivity and its temperature dependence have been determined by impedance spectroscopy. XPS measurements have been carried out to analyze the stability with respect to Li metal.

Li18 P6 N16 -A Lithium Nitridophosphate with Unprecedented Tricyclic [P6 N16 ]18- Ions

Li₁₈ P₆ N₁₆ was synthesized by reaction of LiPN₂ and Li₇ PN₄ at 5.5 GPa and 1273 K employing the multi-anvil technique. It is the first lithium nitridophosphate obtained by high-pressure synthesis. Moreover, it is the first example received by reaction of two ternary lithium nitrides. The combination of high-pressure conditions with a Li₃ N flux enabled a complete structure determination using single-crystal X-ray diffraction. The hitherto unknown tricyclic [P₆ N₁₆ ]^18- anion is composed of six vertex-sharing PN₄ tetrahedra forming one vierer- and two additional dreier-rings. To confirm the structure, Rietveld refinement, ⁷ Li and ³¹ P solid-state NMR spectroscopy, FTIR spectroscopy and EDX measurements were carried out. To validate the ionic properties, the migration pathways of the Li⁺ ions were evaluated, and the conductivity and its temperature dependence were determined by impedance spectroscopy measurements. In order to obtain a clearer picture of the formation mechanism of this compound class, different synthetic approaches were compared, enabling targeted syntheses of unprecedented P/N-anion topologies with intriguing properties.

An unusual nitride network of aluminum-centered octahedra and phosphorus-centered tetrahedra and structure determination from microcrystalline samples

Aluminum coordinated by six nitrogen atoms was realized in a new highly condensed network which was obtained via HP–HT synthesis at 5 GPa.

Recent progress in luminescence tuning of Ce3+and Eu2+-activated phosphors for pc-WLEDs

This review is devoted to several approaches to realize spectral tuning for improving the luminescence performance of Ce³⁺and Eu²⁺-activated pc-WLED phosphors.