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

摘要

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 (Ksub0/sub?=?428(10) GPa), and very hard (nanoindentation hardness 36.7(8) GPa) rhenium nitride pernitride Resub2/sub(Nsub2/sub)(N)sub2/sub. Unlike known transition metals pernitrides Resub2/sub(Nsub2/sub)(N)sub2/sub contains both pernitride Nsub2/subsup4-/sup and discrete Nsup3-/sup anions, which explains its exceptional properties. Resub2/sub(Nsub2/sub)(N)sub2/sub 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, NHsub4/subNsub3/sub, in a large-volume press at 33?GPa. Although metallic bonding is typically seen incompatible with intrinsic hardness, Resub2/sub(Nsub2/sub)(N)sub2/sub turned to be at a threshold for superhard materials.