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High-pressure chemistry of carbon nitride materials

机译：碳氮化物质的高压化学

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The composition and properties of the sp~2-bonded carbon nitride precursor paracyanogen (pCN) has been studied at high pressures and temperatures. Paracyanogen decomposes to carbon and molecular nitrogen with the decomposition temperature increasing with pressure over the range of 3 to 19 GPa. Prior to decomposition, pCN can be transformed to an atmospheric-pressure quenchable phase that is more than 25percent higher in density and over an order of magnitude harder than the starting material. Structural analysis of this quenchable phase shows, however, that it consists of a sp~2-bonded network. In addition, the decomposition kinetics of paracyanogen have been studied in detail. Rapid, self-propagating decomposition occurs above a threshold temperature. Below this, decomposition rates exhibit an Arrhenius behavior with activation energy and volume of 2.7 eV and 3.9 A~3, respectively The decomposition rates depend on the nitrogen density and decrease significantly with lower nitrogen concentration. Kinetic effects favoring a graphite-like, sp~2-bonded structure may preclude the high-pressure synthesis of superhard, sp~3-bonded carbon nitride solids below their thermodynamic stability limit, unless an optimally designed precursor is employed.
机译：SP的组成和性质〜2键合的碳氮化物的前体paracyanogen（PCN）已经研究了在高的压力和温度。 Paracyanogen分解成碳和氮分子与分解温度与压力超过3至19 GPA的范围内增加。之前分解，PCN可转化为常压淬火阶段是超过25percent更高的密度和超过一个数量级比起始材料更硬。这一淬火阶段示出的结构分析，但是，它由一个SP〜2键合的网络。此外，paracyanogen的分解动力学进行了研究，详细。迅速，自传播发生分解阈值温度以上。低于此，分解率表现出与活化能和2.7电子伏特的体积和3.9 A〜3，分别分解速率取决于氮浓度和较低的氮浓度降低显著阿伦尼乌斯行为。有利于一类石墨，SP〜2键合的结构动力学效应可能排除超硬的高压合成，SP〜3键合的碳氮化物的固体低于它们的热力学稳定性的限制，除非使用最佳设计的前体。

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