Nitriding synthesis and structural change of phosphorus nitrides at high pressures

Abstract

The phase stability of γ‐P3N5 and the possible formation of new phosphorus nitrides were investigated via high‐pressure in situ Raman spectroscopy, X‐ray diffraction measurements, and first‐principles calculations up to approximately 80 GPa. In this study, γ‐P3N5 was synthesized via the direct nitridation of black phosphorus at a pressure approximately above 12 GPa. The Raman spectrum, bulk modulus (K0 = 130.27(43) GPa), and compression behaviors (order of axial compressibility: βc > βa > βb) were experimentally measured for the first time. These experimental results were in good agreement with those of first‐principles calculations. Our high‐pressure in situ measurements and first‐principles calculations revealed that γ‐P3N5 persisted up to 80 GPa at room temperature. The compression of γ‐P3N5 proceeded with the folding of the layer consisting of the corner‐ and edge‐sharing PN4 and PN5. The present findings indicate that the P–N bonding with a low coordination number (PN4 and PN5) is preferable and stabilized for phosphorus nitride over a wide pressure range. However, laser heating between 67 and 70 GPa in the presence of nitrogen resulted in the formation of new PxNy, which included the possibility of a new high‐pressure P3N5 phase. The Raman scattering measurements along with the decompression demonstrated that the local structure of the newly synthesized PxNy metastably persisted at atmospheric pressure. The present experimental and theoretical studies on phosphorus nitrides offer new insights into the high‐pressure behaviors of covalent compounds consisting of highly coordinated polyhedra.

High-Pressure and High-Temperature Chemistry of Phosphorus and Nitrogen: Synthesis and Characterization of α- and γ-P3N5

“…Our lattice parameters are in agreement with those recently published by Niwa et al 27 for γ-P 3 N 5 recovered under ambient conditions after laser heating P and N 2 at a slightly higher pressure of 12 GPa (a = 12.8905(7) Å, b = 2.6153(3) Å, and c = 4.4056(3)), even though the laser-heating temperature is not reported in their paper, thus making unclear whether, according to their laser-heating pressure, reactivity in their case occurred in liquid or in crystalline p-sc P. 6,7 The different diffraction signal detected in the outer portions of the laser-heated area revealed instead, among diffuse scattering, reflections compatible with a 0kl layer of the α-P 3 N 5 phase (Figure 6). On the basis of the five most prominent reflections (010, 01̅ 0, 020, 012, and 012̅ ), two lattice parameters of α-P 3 N 5 (b and c) out of four (a, b, c, and β) were determined as a function of pressure by fitting the individual reflections.…”

“…Our lattice parameters are in agreement with those recently published by Niwa et al for γ-P 3 N 5 recovered under ambient conditions after laser heating P and N 2 at a slightly higher pressure of 12 GPa ( a = 12.8905(7) Å, b = 2.6153(3) Å, and c = 4.4056(3)), even though the laser-heating temperature is not reported in their paper, thus making unclear whether, according to their laser-heating pressure, reactivity in their case occurred in liquid or in crystalline p-sc P. , …”

“…The observed anisotropic compressibility of γ-P 3 N 5 is in agreement with previous calculations 21 and clearly emerges from the pressure evolution of the relative values of a, b, and c with respect to their ambient pressure values (Figure 8 lower panel). Also in this case the comparison with recent experimental data 27 highlights the higher experimentally investigated pressure range and the higher number of pressure points in our data. Concerning α-P 3 N 5 , the pressure variation of the c parameter, despite some data scattering, exhibits a clear monotonous decrease with pressure on compression at up to ∼20 GPa.…”

“…While this manuscript was in preparation, a paper on the same topic was published by a Japanese group led by Hasegawa . Whereas some findings of the recent paper are consistent with our previous results, , relevant differences apply, leading to contrasting conclusions, particularly concerning the comprehension of the reactive process and the characterization of the products.…”

Revealing Phosphorus Nitrides up to the Megabar Regime: Synthesis of α′‐P3N5, δ‐P3N5 and PN2

“…[17][18][19] This gap in our empirical understanding of non-metal nitrides is especially striking based on the significant efforts that were devoted to their synthesis, particularly in binary phosphorus nitrides. Still, the many experimental studies, [18][19][20][21] supported by theoretical calculations, [14,22,23] amounted to the synthesis of three P3N5 polymorphs, namely α-and β-P3N5, both formed at near ambient conditions, [18,20] and γ-P3N5 produced at 11 GPa and 1500 K. [19] The exact crystal structure of β-P3N5 is still unknown. [18,20] α-P3N5 can be represented by the Niggli formula [24] 𝑃 [ ] 𝑁 [ ] 𝑁 [ ] -where the coordination number of a given atom is provided in superscripted square brackets (i.e.…”