Structure of theAl13Co4(100) surface: Combination of surface x-ray diffraction andab initiocalculations

Abstract

The structure of the quasicrystalline approximant Al 13 Co 4 (100) has been determined by surface x-ray diffraction (SXRD) and complementary density-functional-theory (DFT) calculations. Thanks to the use of a two-dimensional pixel detector, which speeds up the data acquisition enormously, an exceptionally large set of experimental data, consisting of 124 crystal truncation rods, has been collected and used to refine this complex structure of large unit cell and low symmetry. Various models were considered for the SXRD analysis. The best fit is consistent with a surface termination at the puckered type of planes but with a depletion of the protruding Co atoms. The surface energy of the determined surface model was calculated using DFT, and it takes a rather low value of 1.09 J/m 2. The results for the atomic relaxation of surface planes found by SXRD or DFT were in excellent agreement. This work opens up additional perspectives for the comprehension of related quasicrystalline surfaces.

Catalytic properties of Al13TM4complex intermetallics: influence of the transition metal and the surface orientation on butadiene hydrogenation

“…Each protruding surface TM atom is surrounded by a pentagonal arrangement of Al atoms, leading to the isolation of TM atoms at the surface. Under UHV, this surface model has been experimentally observed in the case of m-Al 13 Fe 4 (010), but not for o-Al 13 Co 4 (100) and m-Al 13 Ru 4 (010) [39,41,50]. However, some operating conditions may stabilize this model (Gaudry et al, in preparation), which has already been postulated to explain the catalytic activity of o-Al 13 Co 4 (100) towards the semi-hydrogenation of acetylene [31].…”

“…The combination of experimental measurements with theoretical calculations is crucial here. Indeed, surface-science studies achieved under ultra-high vacuum (UHV) have already highlighted that the pseudo 10-fold surface structures of these compounds differ: a surface reconstruction is observed for Al 13 Ru 4 (010) [39], but not for Al 13 Co 4 (100) and Al 13 Fe 4 (010) [40][41][42]. The surface structure and composition determined under UHV are also different between Al 13 Co 4 (100) and Al 13 Fe 4 (010).…”

Catalytic activation of a non-noble intermetallic surface through nanostructuration under hydrogenation conditions revealed by atomistic thermodynamics

“…A possible reaction path was identified by first principles calculations on the Al 13 Co 4 (100) surface, with energy barriers similar to the ones calculated for conventional Pd and Pd-Ag catalysts 33 . However, the starting point of this investigation was a surface model derived from a theoretical cleavage, which appears to be inconsistent with the experimental observations of the surface prepared by sputteringannealing under UHV [23][24][25] , and for which rather large barriers have been calculated 34 . Thus the question of the surface structure under catalytic hydrogenation conditions remained open.…”

“…Al 13 TM 4 (TM = Fe, Co) complex intermetallic compounds have recently shown unexpected performances in the partial hydrogenation of alkynes 2,19 and alkadienes 4,20,21 . The bulk and surface structures of these compounds, considered as low scale prototypes of Al-based decagonal quasicrystals, have been extensively studied since several years [22][23][24][25][26][27][28][29][30][31][32] . A possible reaction path was identified by first principles calculations on the Al 13 Co 4 (100) surface, with energy barriers similar to the ones calculated for conventional Pd and Pd-Ag catalysts 33 .…”

The complex energy landscape of non-noble quasicrystalline approximant surfaces induced by their bulk cluster substructure: application to catalysis

“…A visualization of the structure as a cage-compound was then proposed, based on quantum chemical calculations, each cage containing one TM-Al-TM molecular group ( While the bulk atomic arrangements of the Al13TM4 compounds are very similar, the structures of their pseudo-10fold surfaces differ. The cluster substructure is preserved up to the Al13Fe4(010) surface, but Al13Co4(100) presents an Al-rich dense termination [3,4]. The situation is even more complex for Al13Ru4(010), since a surface reconstruction is observed experimentally [5].…”