United in Nitride: The Highly Condensed Boron Phosphorus Nitride BP 3 N 6

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.

Discovery of Two Polymorphs of TiP 4 N 8 Synthesized from Binary Nitrides

TiP₄N₈ was obtained from the binary nitrides TiN and P₃N₅ upon addition of NH₄F as a mineralizer at 8 GPa and 1400 °C. An intricate interplay of disorder and polymorphism was elucidated by in situ temperature‐dependent single‐crystal X‐ray diffraction, STEM‐HAADF, and the investigation of annealed samples. This revealed two polymorphs, which consist of dense networks of PN₄ tetrahedra (degree of condensation κ=0.5) and either augmented triangular TiN₇ prisms or triangular TiN₆ prisms for α‐ and β‐TiP₄N₈, respectively. The structures of TiP₄N₈ exhibit body‐centered tetragonal (bct) framework topology. DFT calculations confirm the measured band gaps of α‐ and β‐TiP₄N₈ (1.6–1.8 eV) and predict the thermochemistry of the polymorphs in agreement with the experiments.

High-Pressure High-Temperature Synthesis of Mixed Nitridosilicatephosphates and Luminescence of AESiP3 N7 :Eu2+ (AE=Sr, Ba)

Tetrahedra-based nitrides with network structures have emerged as versatile materials with a broad spectrum of properties and applications. Both nitridosilicates and nitridophosphates are well-known examples of such nitrides that upon doping with Eu²⁺ exhibit intriguing luminescence properties, which makes them attractive for applications. Nitridosilicates and nitridophosphates show manifold structural variability; however, no mixed nitridosilicatephosphates except SiPN₃ and SiP2N4NH have been described so far. The compounds AESiP₃ N₇ (AE=Sr, Ba) were synthesized by a high-pressure high-temperature approach using the multianvil technique (8 GPa, 1400-1700 °C) starting from the respective alkaline earth azides and the binary nitrides P₃ N₅ and Si₃ N₄ . The latter were activated by NH₄ F, probably acting as a mineralizing agent. SrSiP₃ N₇ and BaSiP₃ N₇ were obtained as single crystals. They crystallized in the barylite-1O (M=Sr) and barylite-2O structure types (M=Ba), respectively, with P and Si being occupationally disordered. Cation disorder was further supported by solid-state NMR spectroscopy and energy-dispersive X-ray spectroscopy (EDX) mapping of BaSiP₃ N₇ with atomic resolution. Upon doping with Eu²⁺ , both compounds showed blue emission under UV excitation.

Synthesis of Nitride Zeolites in a Hot Isostatic Press

The recently introduced nitridophosphate synthesis in a hot isostatic press (HIP) enabled simple access to large‐scale product quantities starting from exclusively commercially available starting materials. Herein, we show that this method is suitable for the synthesis of highly condensed functional nitridophosphates, as well. Hence, the syntheses of the nitridophosphate zeolites Ba₃P₅N₁₀X (X=Cl, Br) are presented as proof of concept for this innovative access. Furthermore, samples of unprecedented Sr₃P₅N₁₀X (X=Cl, Br) were prepared and characterized to demonstrate the advantages of this synthetic approach over commonly used methods. Luminescence investigations on Eu²⁺‐doped samples of AE₃P₅N₁₀X (AE=Sr, Ba; X=Cl, Br) were carried out and characteristics of observed emission bands are discussed.

Post-Synthetic Modification: Systematic Study on a Simple Access to Nitridophosphates

Nitridophosphates are a well‐studied class of nitrides with diverse materials properties, such as luminescence or ion conductivity. Despite the growing interest in this compound class, their synthesis mostly works through direct combination of starting materials. Herein, we present a systematic study on a promising method for post‐synthetic modification by treating pre‐synthesized nitridophosphates with halides under elevated pressures and temperatures. Herein, we focus on the applicability of this approach to P/N compounds with different degrees of condensation. Accordingly, BaP₂N₄, Ba₃P₅N₁₀Br, SrH₄P₆N₁₂, CaP₈N₁₄, and Ca₂PN₃ are investigated as model compounds for framework‐, layer‐, and chain‐type nitridophosphates. The formation of structurally related, as well as, completely unrelated compounds, compared to the starting materials, shows the great potential of the approach, which increases the synthetic possibilities for nitridophosphates significantly.

HIP to be Square: Simplifying Nitridophosphate Synthesis in a Hot Isostatic Press

(Oxo)Nitridophosphates have recently been identified as a promising compound class for application in the field of solid-state lighting. Especially, the latest medium-pressure syntheses under ammonothermal conditions draw attention of the semiconductor and lighting industry on nitridophosphates. In this contribution, we introduce hot isostatic presses as a new type of medium-pressure synthetic tool, further simplifying nitridophosphate synthesis. In a second step, phosphorus nitride was replaced as starting material by red phosphorus, enabling the synthesis of Ca₂ PN₃ as model compound, starting only from readily available compounds. Moreover, first luminescence investigations on Eu²⁺ -doped samples reveal Ca₂ PN₃ :Eu²⁺ as a promising broad-band red-emitter (λ_em =650 nm; fwhm=1972 cm^-1 ). Besides simple handling, the presented synthetic method offers access to large sample volumes, and the underlying reaction conditions facilitate single-crystal growth, required for excellent optical properties.

Boron Phosphorus Nitride at Extremes: PN6 Octahedra in the High-Pressure Polymorph β-BP3 N6

The high-pressure behavior of non-metal nitrides is of special interest for inorganic and theoretical chemistry as well as materials science, as these compounds feature intriguing elastic properties. The double nitride α-BP₃ N₆ was investigated by in situ single-crystal X-ray diffraction (XRD) upon cold compression to a maximum pressure of about 42 GPa, and its isothermal bulk modulus at ambient conditions was determined to be 146(6) GPa. At maximum pressure the sample was laser-heated, which resulted in the formation of an unprecedented high-pressure polymorph, β-BP₃ N₆ . Its structure was elucidated by single-crystal XRD, and can be described as a decoration of a distorted hexagonal close packing of N with B in tetrahedral and P in octahedral voids. Hence, β-BP₃ N₆ is the first nitride to contain PN₆ octahedra, representing the much sought-after proof of principle for sixfold N-coordinated P that has been predicted for numerous high-pressure phases of nitrides.

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.