Phenakite‐Type BeP₂N₄—A Possible Precursor for a New Hard Spinel‐Type Material

Abstract

BeP(2)N(4) was synthesized in a multi-anvil apparatus starting from Be(3)N(2) and P(3)N(5) at 5 GPa and 1500 degrees C. The compound crystallizes in the phenakite structure type (space group R3, no. 148) with a=1269.45(2) pm, c=834.86(2) pm, V=1165.13(4) x 10(6) pm(3) and Z=18. As isostructural and isovalence-electronic alpha-Si(3)N(4) transforms into beta-Si(3)N(4) at high pressure and temperature, we studied the phase transition of BeP(2)N(4) into the spinel structure type by using density functional theory calculations. The predicted transition pressure of 24 GPa is within the reach of today's state of the art high-pressure experimental setups. Calculations of inverse spinel-type BeP(2)N(4) revealed this polymorph to be always higher in enthalpy than either phenakite-type or spinel-type BeP(2)N(4). The predicted bulk modulus of spinel-type BeP(2)N(4) is in the range of corundum and gamma-Si(3)N(4) and about 40 GPa higher than that of phenakite-type BeP(2)N(4). This finding implies an increase in hardness in analogy to that occurring for the beta- to gamma-Si(3)N(4) transition. In hypothetical spinel-type BeP(2)N(4) the coordination number of phosphorus is increased from 4 to 6. So far only coordination numbers up to 5 have been experimentally realized (gamma-P(3)N(5)), though a sixfold coordination for P has been predicted for hypothetic delta-P(3)N(5). We believe, our findings provide a strong incentive for further high-pressure experiments in the quest for novel hard materials with yet unprecedented structural motives.

Electronic structure and physical properties of the spinel-type phase of BeP2N4from all-electron density functional calculations

“…In this context, Ga 3 O 3 N 14 , c-Ge 3 N 4 15 and the hypothetical c-Fe 3 N 4 16 have been described in the literature. Another promising isoelectronic compound is BeP 2 N 4 which, under high pressure, might form a spinel-type phase with interesting properties as well 1 . Furthermore, spinel-type BeP 2 N 4 would contain an unprecedented coordination geometry for phosphorus atoms, namely PN 6 octahedra which have only been predicted in the hypothetical δ-P 3 N 5 17 .…”

“…Accordingly, it would be extremely exiting if the spinel-type phase of BeP 2 N 4 with P at the octahedral site could be synthesized and its physical properties could be explored. Recently, density-functional theory based ab initio calculations have supported the possible existence of a spinel-type phase of BeP 2 N 4 at pressures around 24 GPa which are attainable by state-of-the-art high-pressure experimental techniques 1 . High-pressure polymorphs of related polymeric and covalent nitrides (e. g. γ-Si 3 N 4 12, 13 or γ-P 3 N 5 18 ) which were typically synthesized at higher temperatures turned out to be quenchable.…”

“…The calculation of the physical properties for BeP 2 N 4 is based on the experimentally determined structure for the phenakite-type phase and the density functional theory [DFT] predicted structure for the spinel-type phase 1 . Because the experimentally determined structure for the phenakite-type phase using Rietveld refinement on powdered samples may be less accurate, the theoretically refined structure for the phenakite-type BeP 2 N 4 is also used for the electronic structure and bonding calculations 1 .…”

Nitridophosphate – eine Erfolgsgeschichte der Nitridsynthese

“…[25][26][27][28] Ein Doppelnitrid ist allerdings nicht direkt mit einem Doppeloxid vergleichbar, da sich Letzteres auf Kationen mit ähnlicher Elektronegativitätbezieht. [25][26][27][28] Ein Doppelnitrid ist allerdings nicht direkt mit einem Doppeloxid vergleichbar, da sich Letzteres auf Kationen mit ähnlicher Elektronegativitätbezieht.…”

Rivalry under Pressure: The Coexistence of Ambient‐Pressure Motifs and Close‐Packing in Silicon Phosphorus Nitride Imide SiP2N4NH

“…[15,16] Theo utstanding materials properties of non-metal nitrides are even surpassed by those of their respective high-pressure polymorphs such as c-BN, g-P 3 N 5 ,a nd g-Si 3 N 4 ,w hich feature improved mechanical properties such as increased hardness and bulk moduli. [19] Thus,t ransitions from ambient-pressure to high-pressure polymorphs involve fundamental changes in both the structural and materials properties and are of fundamental interest for high-pressure and materials sciences as well as inorganic chemistry. [19] Thus,t ransitions from ambient-pressure to high-pressure polymorphs involve fundamental changes in both the structural and materials properties and are of fundamental interest for high-pressure and materials sciences as well as inorganic chemistry.…”