The Hardest Superconducting Metal Nitride.
The Hardest Superconducting Metal Nitride.
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DOI：
10.1038/srep13733
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发表时间：
2015-09-03
影响因子：
4.6
通讯作者：
Zhao Y
中科院分区：
文献类型：
--
作者：
Wang S;Antonio D;Yu X;Zhang J;Cornelius AL;He D;Zhao Y
过渡金属（TM）氮化物是一类具有广泛性质和应用的化合物。硬超导氮化物对于在诸如涂覆和高应力（例如，机电系统）。然而，大多数已知的TM氮化物以岩盐结构结晶，该结构不利于抵抗剪切应变，并且它们表现出相对低的压痕硬度，通常在10-20 GPa的范围内。本文报道了在3.5GPa下通过离子交换反应合成六方相δ-MoN和立方相γ-MoN。最终产物呈块状，微晶尺寸为50 - 80 μm。基于单晶的压痕测试，六方相δ-MoN具有约30 GPa的优异硬度，比立方相γ-MoN（约23 GPa）高30%，是迄今为止已知的金属氮化物中最硬的。与立方相相比，六方相硬度的提高主要是由于Mo-N共价键网络的扩展。测得的δ-MoN和立方γ-MoN的超导转变温度分别为13.8和5.5K，与以前的测量结果符合得很好。
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.