Ionic high-pressure form of elemental boron
Ionic high-pressure form of elemental boron
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元素硼的离子高压形式
DOI：
10.1038/nature07736
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发表时间：
2009-02-12
期刊：
影响因子：
64.8
通讯作者：
Solozhenko, Vladimir L.
中科院分区：
文献类型：
--
作者：
Oganov, Artem R.;Chen, Jiuhua;Solozhenko, Vladimir L.
硼是一种化学复杂的元素。自1808年宣布发现这种元素以来，争议一直笼罩着它：这种新“元素”原来是一种含硼量低于60 - 70%的化合物，直到1909年才获得了纯度为99%的硼(1)。虽然我们现在知道至少有16种多晶态(2)，但硼的稳定相即使在环境条件下也尚未在实验中确定(3)。硼的复杂性来自于挫折：在元素周期表中，硼位于金属和绝缘体之间，它只有三个价电子，这有利于金属性，但它们足够局限于绝缘状态。然而，金属状态和绝缘状态之间的这种微妙平衡很容易被压力、温度和杂质所改变。在这里，我们报告了高压实验和从头算演化晶体结构预测的结果（4,5），这些结果探索了硼在压力下的结构稳定性，并引人注目地揭示了部分离子高压硼相。该新相在19 ~ 89 GPa之间稳定，可淬至环境条件，具有迄今未知的结构（空间群Pnnm，单元胞中有28个原子），由二十面体B（12）簇和B(2)对以NaCl-型排列组成。我们发现相的离子性影响其电子带隙、红外吸附和介电常数，这是由于B(2)对和B（12）团簇的不同电子性质以及它们之间产生的电荷转移引起的。
Boron is an element of fascinating chemical complexity. Controversies have shrouded this element since its discovery was announced in 1808: the new 'element' turned out to be a compound containing less than 60 - 70% of boron, and it was not until 1909 that 99% pure boron was obtained(1). And although we now know of at least 16 polymorphs(2), the stable phase of boron is not yet experimentally established even at ambient conditions(3). Boron's complexities arise from frustration: situated between metals and insulators in the periodic table, boron has only three valence electrons, which would favour metallicity, but they are sufficiently localized that insulating states emerge. However, this subtle balance between metallic and insulating states is easily shifted by pressure, temperature and impurities. Here we report the results of high- pressure experiments and ab initio evolutionary crystal structure predictions(4,5) that explore the structural stability of boron under pressure and, strikingly, reveal a partially ionic high-pressure boron phase. This new phase is stable between 19 and 89 GPa, can be quenched to ambient conditions, and has a hitherto unknown structure ( space group Pnnm, 28 atoms in the unit cell) consisting of icosahedral B(12) clusters and B(2) pairs in a NaCl- type arrangement. We find that the ionicity of the phase affects its electronic bandgap, infrared adsorption and dielectric constants, and that it arises from the different electronic properties of the B(2) pairs and B(12) clusters and the resultant charge transfer between them.