Li47 B3 P14 N42 -A Lithium Nitridoborophosphate with [P3 N9 ]12− , [P4 N10 ]10− , and the Unprecedented [B3 P3 N13 ]15− Ion

Nitride Synthesis under High-Pressure, High-Temperature Conditions: Unprecedented In Situ Insight into the Reaction

High-pressure, high-temperature (HP/HT) syntheses are essential for modern high-performance materials. Phosphorus nitride, nitridophosphate, and more generally nitride syntheses benefit greatly from HP/HT conditions. In this contribution, we present the first systematic in situ investigation of a nitridophosphate HP/HT synthesis using the reaction of zinc nitride Zn3N2 and phosphorus(V) nitride P3N5 to the nitride semiconductor Zn2PN3 as a case study. At a pressure of 8 GPa and temperatures up to 1300 °C, the reaction was monitored by energy-dispersive powder X-ray diffraction (ED-PXRD) in a large-volume press at beamline P61B at DESY. The experiments investigate the general behavior of the starting materials under extreme conditions and give insight into the reaction. During cold compression and subsequent heating, the starting materials remain crystalline above their ambient-pressure decomposition points, until a sufficient minimum temperature is reached and the reaction starts. The reaction proceeds via ion diffusion at grain boundaries with an exponential decay in the reaction rate. Raising the temperature above the minimum required value quickly completes the reaction and initiates single-crystal growth. After cooling and decompression, which did not influence the resulting product, the recovered sample was analyzed by energy-dispersive X-ray (EDX) spectroscopy.

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 P1 - ${\mathrel{\mathop{{\rm { 1}}}\limits^{{\rm -}}}}$ 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.

Structure Determination of the Crystalline LiPON Model Structure Li5+x P2 O6-x N1+x with x≈0.9

Non-crystalline lithium oxonitridophosphate (LiPON) is used as solid electrolyte in all-solid-state batteries. Crystalline lithium oxonitridophosphates are important model structures to retrieve analytical information that can be used to understand amorphous phases better. The new crystalline lithium oxonitridophosphate Li_5+x P₂ O_6-x N_1+x was synthesized as an off-white powder by ampoule synthesis at 750-800 °C under Ar atmosphere. It crystallizes in the monoclinic space group P2₁ /c with a=15.13087(11) Å, b=9.70682(9) Å, c=8.88681(7) Å, and β=106.8653(8)°. Two P(O,N)₄ tetrahedra connected by an N atom form the structural motif [P₂ O_6-x N_1+x ]^(5+x)- . The structure was elucidated from X-ray diffraction data and the model corroborated by NMR and infrared spectroscopy, and elemental analyses. Measurements of ionic conductivity show a total ionic conductivity of 6.8×10^-7  S cm^-1 at 75 °C with an activation energy of 0.52±0.01 eV.

(PNSiMe3 )4 (NMe)6 : A Robust Tetravalent Phosphaza-adamantane Scaffold for Molecular and Macromolecular Construction

Tetraarylmethanes and adamantanes are important rigid covalent connectors that play a four-way scaffolding role in molecular and materials chemistry. We report the synthesis of a new tetravalent phosphaza-adamantane cage, (PNSiMe₃ )₄ (NMe)₆ (2), that shows high thermal, air, and redox stability due to its geometry. It nevertheless participates in covalent four-fold functionalization reactions along its periphery. The combination of a robust core and reactive corona makes 2 a convenient inorganic scaffold upon which tetrahedral molecular and macromolecular chemistry can be constructed. This potential is demonstrated by the synthesis of a tetrakis(bis(phosphine)iminium) ion (in compound 3) and the first all P/N poly(phosphazene) network (5).

Supertetrahedral anions in the phosphidosilicates Na1.25Ba0.875Si3P5 and Na31Ba5Si52P83

Solid ionic conductors are one key component of all-solid-state batteries, and recent studies with lithium, sodium and potassium phosphidosilicates revealed remarkable ion conduction capabilities in these compounds. We report the synthesis and crystal structures of two quaternary phosphidosilicates with sodium and barium, which crystallize in new structure types. Na1.25Ba0.875Si3P5 contains layers of T3 supertetrahedra, while Na31Ba5Si52P83 forms defect T5 entities and contains Si-Si bonds and P3 trimers. Though T1-relaxometry data indicate a relatively low activation energy for Na+ migration of 0.16 eV, the crystal structures lack sufficient three-dimensional migration paths necessary for fast sodium ion conductvity.

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.

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.