Previously unknown quasicrystal periodic approximant found in space
Previously unknown quasicrystal periodic approximant found in space
复制标题
在太空中发现以前未知的准晶体周期性近似
作者：
L. Bindi;Joyce Pham;P. Steinhardt
我们报告发现的Al 34 Ni 9 Fe 2，第一个天然已知的周期性晶体近似十边石（Al 71 Ni 24 Fe 5），一个天然准晶组成的周期性堆叠的平面准周期原子秩序和十重对称。这种新矿物已被国际矿物学协会（IMA 2018-038）批准，并正式命名为斜方石，这是因为它与十边石的周期近似物相同。十重岩和斜长十重岩都是在哈蒂尔卡陨石的碎片中发现的。近氧角闪石是在Al-Ni-Fe系中发现的第一种天然准晶近似物。在该系统中，十次准晶相已被报道在约940 °C下转变为Al 13（Fe，Ni）4、Al 3（Fe，Ni）2和液相，并且在800 ° C和850 °C之间转变为Al 13（Fe，Ni）4、Al 3（Fe，Ni）和Al 3（Fe，Ni）2。在实验室中从未观察到过这种陨石，它是在撞击引发的冲击过程中暴露于高压和高温下的陨石中形成的，这一事实表明它可能是一种在高压下稳定的化合物。最突出的结构基序是伪五边形对称亚单元，如五边形双锥，其与三角形双锥共享边缘和拐角，并且使最短的Ni-Al比Ni-Ni接触最大化。
We report the discovery of Al34Ni9Fe2, the first natural known periodic crystalline approximant to decagonite (Al71Ni24Fe5), a natural quasicrystal composed of a periodic stack of planes with quasiperiodic atomic order and ten-fold symmetry. The new mineral has been approved by the International Mineralogical Association (IMA 2018-038) and officially named proxidecagonite, which derives from its identity to periodic approximant of decagonite. Both decagonite and proxidecagonite were found in fragments from the Khatyrka meteorite. Proxidecagonite is the first natural quasicrystal approximant to be found in the Al-Ni-Fe system. Within this system, the decagonal quasicrystal phase has been reported to transform at ~940 °C to Al13(Fe,Ni)4, Al3(Fe,Ni)2 and the liquid phase, and between 800 and 850 °C to Al13(Fe,Ni)4, Al3(Fe,Ni) and Al3(Fe,Ni)2. The fact that proxidecagonite has not been observed in the laboratory before and formed in a meteorite exposed to high pressures and temperatures during impact-induced shocks suggests that it might be a thermodynamically stable compound at high pressure. The most prominent structural motifs are pseudo-pentagonal symmetry subunits, such as pentagonal bipyramids, that share edges and corners with trigonal bipyramids and which maximize shortest Ni–Al over Ni–Ni contacts.