High-pressure synthesis of ultraincompressible hard rhenium nitride pernitride Re2(N2)(N)2 stable at ambient conditions

Maxim Bykov,Ferenc Tasnádi,Anna Pakhomova,Natalia Dubrovinskaia,Hongzhan Fei,Georgios Aprilis,Patrick Feldner,Stella Chariton,Hanns‐Peter Liermann ,Michael Hanfland,Wolfgang Schnick,Eran Greenberg,Igor A Abrikosov,Sebastian Vogel,Timofey Fedotenko,A V Ponomareva ,Tomoo Katsura,Vitali B Prakapenka,Benoit Merle,Leonid Dubrovinsky

doi:10.1038/s41467-019-10995-3

Abstract

High-pressure synthesis in diamond anvil cells can yield unique compounds with advanced properties, but often they are either unrecoverable at ambient conditions or produced in quantity insufficient for properties characterization. Here we report the synthesis of metallic, ultraincompressible (K0 = 428(10) GPa), and very hard (nanoindentation hardness 36.7(8) GPa) rhenium nitride pernitride Re2(N2)(N)2. Unlike known transition metals pernitrides Re2(N2)(N)2 contains both pernitride N24− and discrete N3− anions, which explains its exceptional properties. Re2(N2)(N)2 can be obtained via a reaction between rhenium and nitrogen in a diamond anvil cell at pressures from 40 to 90 GPa and is recoverable at ambient conditions. We develop a route to scale up its synthesis through a reaction between rhenium and ammonium azide, NH4N3, in a large-volume press at 33 GPa. Although metallic bonding is typically seen incompatible with intrinsic hardness, Re2(N2)(N)2 turned to be at a threshold for superhard materials.

Highlights

High-pressure synthesis in diamond anvil cells can yield unique compounds with advanced properties, but often they are either unrecoverable at ambient conditions or produced in quantity insufficient for properties characterization
PtN212, PdN213, IrN214, OsN214, TiN215, RhN216, RuN217, CoN218, and FeN219, containing covalently bound dinitrogen units were recently synthesized in laser-heated diamond anvil cells (LHDACs) via reactions between elemental metal and nitrogen in a pressure range of 40–80 GPa
The search for suitable synthetic strategies, which would enable an appropriate reaction to be realized in a large volume press (LVP) instead of a LHDAC, is an important challenge for high-pressure chemistry and materials sciences

Summary

Introduction

High-pressure synthesis in diamond anvil cells can yield unique compounds with advanced properties, but often they are either unrecoverable at ambient conditions or produced in quantity insufficient for properties characterization. According to the approach formulated by Yeung et al.[1], the design of novel superhard materials should be based on the combination of a metal with high valence electron density with the first-row main-group elements, which form short covalent bonds to prevent dislocations. This conclusion was based on the synthesis of hard borides, such as OsB22, ReB23–5, FeB46, or WB47, whose crystal structures possess covalently bonded boron networks. In this study, focusing on the high-pressure synthesis of nitrogen-rich phases in the Re-N system and the development of new synthetic strategies, we resolved this problem for a rhenium nitride ReN2 with unusual crystal chemistry and unique properties

Methods

Results

Conclusion