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Title: The Hardest Superconducting Metal Nitride

Transition–metal (TM) nitrides are a class of compounds with a wide range of properties and applications. Hard superconducting nitrides are of particular interest for electronic applications under working conditions such as coating and high stress (e.g., electromechanical systems). However, most of the known TM nitrides crystallize in the rock–salt structure, a structure that is unfavorable to resist shear strain, and they exhibit relatively low indentation hardness, typically in the range of 10–20 GPa. Here, we report high–pressure synthesis of hexagonal δ–MoN and cubic γ–MoN through an ion–exchange reaction at 3.5 GPa. The final products are in the bulk form with crystallite sizes of 50 – 80 μm. Based on indentation testing on single crystals, hexagonal δ–MoN exhibits excellent hardness of ~30 GPa, which is 30% higher than cubic γ–MoN (~23 GPa) and is so far the hardest among the known metal nitrides. The hardness enhancement in hexagonal phase is attributed to extended covalently bonded Mo–N network than that in cubic phase. The measured superconducting transition temperatures for δ–MoN and cubic γ–MoN are 13.8 and 5.5 K, respectively, in good agreement with previous measurements.
Authors:
 [1] ;  [2] ;  [3] ;  [3] ;  [2] ;  [4] ;  [5]
  1. University of Nevada, HiPSEC & Physics Dept., Las Vegas, NV (United States); Sichuan University, Chengdu, (China). Inst. of Atomic and Molecular Physics; Los Alamos National Laboratory, Los Alamos, NM (United States)
  2. University of Nevada, HiPSEC & Physics Dept., Las Vegas, NV (United States)
  3. Los Alamos National Lab., NM (United States)
  4. Sichuan University, Chengdu, (China). Inst. of Atomic and Molecular Physics
  5. University of Nevada, HiPSEC & Physics Dept., Las Vegas, NV (United States); Los Alamos National Lab., NM (United States)
Publication Date:
OSTI Identifier:
1214836
Grant/Contract Number:
AC52-06NA25396; AC02-06CH11357; FC52-06NA27684; NA0001974; FG02-99ER45775
Type:
Accepted Manuscript
Journal Name:
Scientific Reports
Additional Journal Information:
Journal Volume: 5; Journal Issue: 09, 2015; Journal ID: ISSN 2045-2322
Publisher:
Nature Publishing Group
Research Org:
Advanced Photon Source (APS), Argonne National Laboratory (ANL), Argonne, IL (United States); Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)
Sponsoring Org:
USDOE National Nuclear Security Administration (NNSA); USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Country of Publication:
United States
Language:
ENGLISH
Subject:
36 MATERIALS SCIENCE; 75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY