Solid ammonia at high pressure: A single-crystal x-ray diffraction study to 123 GPa
Solid ammonia at high pressure: A single-crystal x-ray diffraction study to 123 GPa
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DOI：
10.1103/physrevb.73.174111
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发表时间：
2006-05-01
影响因子：
3.7
通讯作者：
Decremps, F
中科院分区：
文献类型：
--
作者：
Datchi, F;Ninet, S;Decremps, F
在金刚石对顶砧装置中，用X射线衍射研究了室温下固态氨的高压相。尽管在4GPa下发生一级固相转变，但可以获得NH3和ND3的准单晶，并分别压缩到123和62GPa。在4GPa以上观测到的反射与ND3上中子衍射确定的结构是一致的。我们发现了强有力的证据，在12 GPa的NH3和18 GPa的ND3的等对称过渡。这种转变更有可能是由于氢原子的重排，而N原子仍保留在它们的准六方晶系位置上。实验状态方程（EOS）进行比较，从第一性原理计算得出的一个。高于55 GPa的EOS硬化可能表明一些H键的量子无序状态的开始。
The high-pressure phases of solid ammonia have been investigated by x-ray diffraction in a diamond anvil cell at room temperature. Despite the first-order solid phase transition at 4 GPa, quasi-single crystals of NH3 and ND3 could be obtained and compressed to 123 and 62 GPa, respectively. The observed reflections above 4 GPa are compatible with the structure determined by neutron diffraction on ND3. We found strong evidence for an isosymmetric transition at 12 GPa in NH3 and 18 GPa in ND3. This transition is more likely due to rearrangements of the hydrogen atoms, whereas the N atoms remain on their quasi-hcp sites. The experimental equation of state (EOS) is compared to the one derived from first-principles calculations. A stiffening of the EOS above 55 GPa could indicate the onset of a quantum-disordered regime for some of the H bonds.