A complex pseudo-decagonal quasicrystal approximant, Al-37(Co,Ni)(15.5), solved by rotation electron diffraction
2014 (English)In: Journal of applied crystallography, ISSN 0021-8898, E-ISSN 1600-5767, Vol. 47, no 1, 215-221 p.Article in journal (Refereed) Published
Electron diffraction is a complementary technique to single-crystal X-ray diffraction and powder X-ray diffraction for structure solution of unknown crystals. Crystals too small to be studied by single-crystal X-ray diffraction or too complex to be solved by powder X-ray diffraction can be studied by electron diffraction. The main drawbacks of electron diffraction have been the difficulties in collecting complete three-dimensional electron diffraction data by conventional electron diffraction methods and the very time-consuming data collection. In addition, the intensities of electron diffraction suffer from dynamical scattering. Recently, a new electron diffraction method, rotation electron diffraction (RED), was developed, which can overcome the drawbacks and reduce dynamical effects. A complete three-dimensional electron diffraction data set can be collected from a sub-micrometre-sized single crystal in less than 2 h. Here the RED method is applied for ab initio structure determination of an unknown complex intermetallic phase, the pseudo-decagonal (PD) quasicrystal approximant Al-37.0(Co,Ni)(15.5), denoted as PD2. RED shows that the crystal is F-centered, with a = 46.4, b = 64.6, c = 8.2 angstrom. However, as with other approximants in the PD series, the reflections with odd l indices are much weaker than those with l even, so it was decided to first solve the PD2 structure in the smaller, primitive unit cell. The basic structure of PD2 with unit-cell parameters a = 23.2, b = 32.3, c = 4.1 angstrom and space group Pnmm has been solved in the present study. The structure with c = 8.2 angstrom will be taken up in the near future. The basic structure contains 55 unique atoms (17 Co/Ni and 38 Al) and is one of the most complex structures solved by electron diffraction. PD2 is built of characteristic 2 nm wheel clusters with fivefold rotational symmetry, which agrees with results from high-resolution electron microscopy images. Simulated electron diffraction patterns for the structure model are in good agreement with the experimental electron diffraction patterns obtained by RED.
Place, publisher, year, edition, pages
2014. Vol. 47, no 1, 215-221 p.
IdentifiersURN: urn:nbn:se:su:diva-101248DOI: 10.1107/S1600576713029294ISI: 000330485100029OAI: oai:DiVA.org:su-101248DiVA: diva2:701996
FunderSwedish Research CouncilKnut and Alice Wallenberg Foundation, 3DEM-NATUR