P3 N5 Research Articles

Please Mind the Gap: Highly Condensed P-N Networks in LiP4 N7 and Li3-x P6 N11-x (NH)x.

Alkali nitridophosphates AP4 N7 and A3 P6 N11 (A=Na, K, Rb, Cs) have been known for decades. However, their Li homologues have remained elusive. In this work, the highly condensed lithium (imido)nitridophosphates LiP4 N7 and Li3-x P6 N11-x (NH)x (x=1.66(3)) were synthesized from LiPN2 and P3 N5 in the multianvil press at 10 GPa. They constitute the first lithium nitridophosphates with 3D networks exhibiting a degree of condensation larger than 0.5 and high thermal stability. LiP4 N7 crystallizes in the orthorhombic space group P21 21 21 with a=4.5846(6) Å, b=8.0094(11) Å, and c=13.252(2) Å (Z=4). Li3-x P6 N11-x (NH)x crystallizes in the triclinic space group P with Z=2, a=4.6911(11) Å, b=7.024(2) Å, c=12.736(3) Å, α=87.726(11), β=80.279(11), and γ=70.551(12)°. Both compounds are stable against hydrolysis in air.

Finding Order in Disorder: The Highly Disordered Lithium Oxonitridophosphate Double Salt Li8+x P3 O10-x N1+x (x=1.4(5)).

The crystalline lithium oxonitridophosphate Li8+x P3 O10-x N1+x , was obtained in an ampoule synthesis from P3 N5 and Li2 O. The compound crystallizes in the triclinic space group P with a=5.125(2), b=9.888(5), c=10.217(5) Å, α=70.30(2), β=76.65(2), γ=77.89(2)°. Li8+x P3 O10-x N1+x is a double salt, the structure of which contains distinctive complex anion species, namely non-condensed P(O,N)4 tetrahedra, and P(O,N)7 double tetrahedra connected by one N atom. Additionally, there is mixed occupation of O/N positions, which enables further anionic species by variation of O/N occupancies. To characterize these motifs in detail, complementary analytical methods were applied. The double tetrahedron exhibits significant disorder in single-crystal X-ray diffraction. Furthermore, the title compound is a Li+ ion conductor with a total ionic conductivity of 1.2×10-7 S cm-1 at 25 °C, and a corresponding total activation energy of 0.47(2) eV.

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

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.

Coherent Sub-Nanometer Interface between Crystalline and Amorphous Materials Boosts Electrochemical Synthesis of Hydrogen Peroxide.

There are enormous yet largely underexplored exotic phenomena and properties emerging from interfaces constructed by diverse types of components that may differ in composition, shape, or crystal structure. It remains poorly understood the unique properties a coherent interface between crystalline and amorphous materials may evoke, and there lacks a general strategy to fabricate such interfaces. It is demonstrated that by topotactic partial oxidation heterostructures composed of coherently registered crystalline and amorphous materials can be constructed. As a proof-of-concept study, heterostructures consisting of crystalline P3 N5 and amorphous P3 N5 Ox can be synthesized by creating amorphous P3 N5 Ox from crystalline P3 N5 without interrupting the covalent bonding across the coherent interface. The heterostructure is dictated by nanometer-sized short-range-ordered P3 N5 domains enclosed by amorphous P3 N5 Ox matrix, which entails simultaneously fast charge transfer across the interface and bicomponent synergistic effect in catalysis. Such a P3 N5 /P3 N5 Ox heterostructure attains an optimal adsorption energy for *OOH intermediates and exhibits superior electrocatalytic performance toward H2 O2 production by adopting a selectivity of 96.68% at 0.4 VRHE and a production rate of 321.5 mmol h-1 gcatalyst -1 at -0.3 VRHE . The current study provides new insights into the synthetic strategy, chemical structure, and catalytic property of a sub-nanometer coherent interface formed between crystalline and amorphous materials.

Comprehensive Investigation of Anion Species in Crystalline Li+ ion Conductor Li27-x [P4 O7+x N9-x ]O3 (x≈1.9(3)).

The Li+ ion conductor Li27-x [P4 O7+x N9-x ]O3 (x≈1.9) has been synthesized from P3 N5 , Li3 N and Li2 O in a Ta ampoule at 800 °C under Ar atmosphere. The cubic compound crystallizes in space group I 3d with a=12.0106(14) Å and Z=4. It contains both non-condensed [PO2 N2 ]5- and [PO3 N]4- tetrahedra as well as O2- ions, surrounded by Li+ ions. Charge neutrality is achieved by partial occupancy of Li positions, which was refined with neutron powder diffraction data. Measurements of the partial ionic and electronic conductivity show a total ionic conductivity of 6.6×10-8 S cm-1 with an activation energy of 0.46±0.02 eV and a bulk ionic conductivity of 4×10-6 S cm-1 at 25 °C, which is close to the ionic conductivity of amorphous lithium nitridophosphate. This makes Li27-x [P4 O7+x N9-x ]O3 an interesting candidate for investigation of structural factors affecting ionic conductivity in lithium oxonitridophosphates.

Structural Influence of Lone Pairs in GeP2 N4 , a Germanium(II) Nitridophosphate.

Owing to their widespread properties, nitridophosphates are of high interest in current research. Explorative high-pressure high-temperature investigations yielded various compounds with stoichiometry MP2 N4 (M=Be, Ca, Sr, Ba, Mn, Cd), which are discussed as ultra-hard or luminescent materials, when doped with Eu2+ . Herein, we report the first germanium nitridophosphate, GeP2 N4 , synthesized from Ge3 N4 and P3 N5 at 6 GPa and 800 °C. The structure was determined by single-crystal X-ray diffraction and further characterized by energy-dispersive X-ray spectroscopy, density functional theory calculations, IR and NMR spectroscopy. The highly condensed network of PN4 -tetrahedra shows a strong structural divergence to other MP2 N4 compounds, which is attributed to the stereochemical influence of the lone pair of Ge2+ . Thus, the formal exchange of alkaline earth cations with Ge2+ may open access to various compounds with literature-known stoichiometry, however, new structures and properties.

Revealing Phosphorus Nitrides up to the Megabar Regime: Synthesis of α'-P3 N5, δ-P3 N5 and PN2.

Non-metal nitrides are an exciting field of chemistry, featuring a significant number of compounds that can possess outstanding material properties. These properties mainly rely on maximizing the number of strong covalent bonds, with crosslinked XN6 octahedra frameworks being particularly attractive. In this study, the phosphorus-nitrogen system was studied up to 137 GPa in laser-heated diamond anvil cells, and three previously unobserved phases were synthesized and characterized by single-crystal X-ray diffraction, Raman spectroscopy measurements and density functional theory calculations. δ-P3 N5 and PN2 were found to form at 72 and 134 GPa, respectively, and both feature dense 3D networks of the so far elusive PN6 units. The two compounds are ultra-incompressible, having a bulk modulus of K0 =322 GPa for δ-P3 N5 and 339 GPa for PN2 . Upon decompression below 7 GPa, δ-P3 N5 undergoes a transformation into a novel α'-P3 N5 solid, stable at ambient conditions, that has a unique structure type based on PN4 tetrahedra. The formation of α'-P3 N5 underlines that a phase space otherwise inaccessible can be explored through materials formed under high pressure.

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.

Ammonothermal Synthesis, Optical Properties, and DFT Calculations of Mg2 PN3 and Zn2 PN3.

The phosphorus nitrides, Mg2 PN3 and Zn2 PN3 , are wide band gap semiconductor materials with potential for application in (opto)electronics or photovoltaics. For the first time, both compounds were synthesized ammonothermally in custom-built high-temperature, high-pressure autoclaves starting from P3 N5 and the corresponding metals (Mg or Zn). Alkali amides (NaNH2 , KNH2 ) were employed as ammonobasic mineralizers to increase solubility of the starting materials in supercritical ammonia through formation of reactive intermediates. Single crystals of Mg2 PN3 , with length up to 30 μm, were synthesized at 1070 K and 140 MPa. Zn2 PN3 already decomposes at these conditions and was obtained as submicron-sized crystallites at 800 K and 200 MPa. Both compounds crystallize in a wurtzite-type superstructure in orthorhombic space group Cmc21 , which was confirmed by powder X-ray diffraction. In addition, single-crystal X-ray diffraction measurements of Mg2 PN3 were carried out for the first time. To our knowledge, this is the first single-crystal X-ray study of ternary nitrides synthesized by the ammonothermal method. The band gaps of both nitrides were estimated to be 5.0 eV for Mg2 PN3 and 3.7 eV for Zn2 PN3 by diffuse reflectance spectroscopy. DFT calculations were carried out to verify the experimental values. Furthermore, a dissolution experiment was conducted to obtain insights into the crystallization behavior of Mg2 PN3 .

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.

Li12 P3 N9 with Non-Condensed [P3 N9 ]12- -Rings and its High-Pressure Polymorph Li4 PN3 with Infinite Chains of PN4 -Tetrahedra.

Li12 P3 N9 was synthesized by solid-state reaction of Li3 N and P3 N5 at 790 °C. It is made up of non-condensed [P3 N9 ]12- dreier-rings of PN4 -tetrahedra. The corresponding high-pressure polymorph, Li4 PN3 , was synthesized under high-pressure/high-temperature conditions from Li12 P3 N9 or LiPN2 and Li7 PN4 at 6 or 7 GPa, respectively, using the multianvil technique. Li4 PN3 is the first lithium catena-nitridophosphate and contains PN3 zweier-chains of corner sharing PN4 -tetrahedra. To confirm the structure elucidated from single-crystal X-ray data, Rietveld refinement, 6 Li, 7 Li, and 31 P solid-state NMR spectroscopy, FTIR spectroscopy and EDX measurements were carried out. To examine the phase transition of Li12 P3 N9 to Li4 PN3 at 6 GPa and to corroborate the latter as the corresponding high-pressure polymorph, DFT calculations were conducted. Electronic band gap and electron localization function (ELF) calculations were carried out to elucidate the electronic properties and bonding behavior of both polymorphs.

Safer Pyrotechnic Obscurants Based on Phosphorus(V) Nitride.

The potential of phosphorus(V) nitride, P3 N5 , as a replacement for red phosphorus, PR , in pyrotechnic obscurants has been theoretically and experimentally investigated. P3 N5 can be safely mixed with KNO3 and even KClO3 and KClO4 . The corresponding formulations are surprisingly insensitive to friction and only mildly impact-sensitive. P3 N5 /KNO3 pyrolants with ξ=20-80 wt % P3 N5 burn 200 times faster than the corresponding mixtures based on PR and generate a dense smoke. Hence obscurants based on P3 N5 /KNO3 have a figure of merit that by far exceeds that of current state-of-the-art PR -based obscurants. Furthermore, unlike PR , which slowly degrades in moist air to phosphoric acids and phosphine (PH3 ), P3 N5 is stable under these conditions and does not produce any acids or PH3 . P3 N5 is hence a safe, stable, and powerful replacement for PR for use in insensitive munitions.

Experiment-Driven Modeling of Crystalline Phosphorus Nitride P3 N5 : Wide-Ranging Implications from a Unique Structure.

Nitridophosphates have emerged as advanced materials due to their structural variability and broad technical applicability. Their binary parent compound P3 N5 , a polymeric network of corner- and edge-sharing PN4 tetrahedra with N and N sites, is a particularly interesting example. We present a study of the band gap and electronic structure of α-P3 N5 by using soft X-ray spectroscopy measurements and DFT calculations. The band gap, which is crucial for all applications, is measured to be 5.87±0.20 eV. This agrees well with the calculated, indirect band gap of 5.21 eV. The density of states are found to show dramatic variation between the nonequivalent N sites and a high degree of covalency. Coupled to these results is what is, to our knowledge, the largest core hole shift reported to date for a soft X-ray absorption spectrum. We propose an intuitive bonding scheme for α-P3 N5 that explains the observed band gap and unique density of states, while providing a framework for predicting these properties in known and yet to be discovered PN compounds. We briefly consider the implications of these results for new low-dimensional P and PN materials, which alongside graphene, could become important materials for nanoelectronics.

Luminescent nitridophosphates CaP2 N4 :Eu(2+) , SrP2 N4 :Eu(2+) , BaP2 N4 :Eu(2+) , and BaSr2 P6 N12 :Eu(2.).

Nitridophosphates MP2 N4 :Eu(2+) (M=Ca, Sr, Ba) and BaSr2 P6 N12 :Eu(2+) have been synthesized at elevated pressures and 1100-1300 °C starting from the corresponding azides and P3 N5 with EuCl2 as dopant. Addition of NH4 Cl as mineralizer allowed for the growth of single crystals. This led to the successful structure elucidation of a highly condensed nitridophosphate from single-crystal X-ray diffraction data (CaP2 N4 :Eu(2+) (P63 , no. 173), a=16.847(2), c=7.8592(16) Å, V=1931.7(6) Å(3) , Z=24, 2033 observed reflections, 176 refined parameters, wR2 =0.096). Upon excitation by UV light, luminescence due to parity-allowed 4f(6) ((7) F)5d(1) →4f(7) ((8) S7/2 ) transition was observed in the orange (CaP2 N4 :Eu(2+) , λmax =575 nm), green (SrP2 N4 :Eu(2+) , λmax =529 nm), and blue regions of the visible spectrum (BaSr2 P6 N12 :Eu(2+) and BaP2 N4 :Eu(2+) , λmax =450 and 460 nm, respectively). Thus, the emission wavelength decreases with increasing ionic radius of the alkaline-earth ions. The corresponding full width at half maximum values (2240-2460 cm(-1) ) are comparable to those of other known Eu(2+) -doped (oxo)nitrides emitting in the same region of the visible spectrum. Following recently described quaternary Ba3 P5 N10 Br:Eu(2+) , this investigation represents the first report on the luminescence of Eu(2+) -doped ternary nitridophosphates. Similarly to nitridosilicates and related oxonitrides, Eu(2+) -doped nitridophosphates may have the potential to be further developed into efficient light-emitting diode phosphors.

Auger parameter measurements of phosphorus compounds for characterization of phosphazenes

X-ray generated photoelectron and Auger transition data for several phosphorus reference compounds, including PCl3, P3 N5, P2 O5, (C6 H5 )3 P(C5 H4 ), (C6 H5 )4 PBr, KH2 PO4 , NH4H2PO4, and NH4 PF6 are presented. These data have been used to determine the relative ionicity and polarizability of phosphorus in the chlorophosphazene trimer ([NPCl2 ]3 ) and polymer ([NPCl2 ]n ). The results support recent molecular-orbital calculations that predict a highly polarized backbone bond in the phosphazenes. Furthermore, the chlorophosphazene polymer was observed to have a greater value for the Auger parameter than the chlorotrimer, indicating that the bonding environment surrounding the polymer is more polarizable than that surrounding the trimer.