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In situ observation of quasimelting of diamond and reversible graphite-diamond phase transformations

机译：金刚石和可逆石墨-金刚石相变的准模拟的原位观察

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Because of technique difficulties in achieving the extreme high-pressure and high-temperature (HPHT) simultaneously, direct observation of the structures of carbon at extreme HPHT conditions has not been possible. Banhart and Ajayan discovered remarkably that carbon onions can act as nanoscopic pressure cells to generate high pressures. By heating carbon onions to similar to 700 degrees C and under electron beam irradiation, the graphite-to-diamond transformation was observed in situ by transmission electron microscopy (TEM). However, the highest achievable temperature in a TEM heating holder is less than 1000 degrees C. Here we report that, by using carbon nanotubes as heaters and carbon onions as high-pressure cells, temperatures higher than 2000 degrees C and pressures higher than 40 GPa were achieved simultaneously in carbon onions. At such HPHT conditions and facilitated by electron beam irradiation, the diamond formed in the carbon onion cores frequently changed its shape, size, orientation, and internal structure and moved like a fluid, implying that it was in a quasimelting state. The fluctuation between the solid phase of diamond and the fluid/amorphous phase of diamond-like carbon, and the changes of the shape, size, and orientation of the solid diamond, were attributed to the dynamic crystallization of diamond crystal from the quasimolten state and the dynamic graphite-diamond phase transformations. Our discovery offers unprecedented opportunities to studying the nanostructures of carbon at extreme conditions in situ and at an atomic scale.
机译：由于在同时实现极高压和高温（HPHT）方面存在技术困难，因此无法在极端HPHT条件下直接观察碳的结构。 Banhart和Ajayan显着发现碳洋葱可以充当产生高压的纳米压力电池。通过将碳洋葱加热到大约700摄氏度并在电子束照射下，通过透射电子显微镜（TEM）在原位观察到石墨到金刚石的转变。但是，在TEM加热支架中可达到的最高温度低于1000摄氏度。在此我们报告，通过使用碳纳米管作为加热器，将碳洋葱用作高压电池，温度高于2000摄氏度，压力高于40 GPa在碳洋葱中同时获得。在这种高温高压条件下，在电子束辐照的促进下，形成在碳洋葱芯上的钻石经常改变其形状，大小，取向和内部结构，并像流体一样运动，这表明它处于准拟晶态。金刚石固相和类金刚石碳的流体/非晶相之间的波动以及固体金刚石的形状，尺寸和取向的变化是由于金刚石晶体从准熔融态和动态结晶所致。动态石墨-金刚石相变。我们的发现为在极端条件下原位和原子尺度研究碳的纳米结构提供了前所未有的机会。

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