Partial pair distribution functions in icosahedral Al-Mn studied by contrast variation in neutron diffraction

Abstract

Des phases icosaédriques des systèmes Al-Mn et Al-(MnFeCr) ont été étudiées par diffraction des neutrons, jusqu'à des vecteurs de diffusion de 16 Å-1. Les trois fonctions de distribution de paires partielles ont été calculées. On a pu ainsi confirmer sans ambiguïté le caractère parfaitement isomorphe de la substitution du Mn par 03C3-FeCr. Les corrélations de paires atomiques apparaissent très semblables à celles de la phase cristalline 03B1(AlMnSi). En particulier, les plus courtes distances Mn-Mn sont trouvées à 4,47 et 4,97 A. Abstract.-Icosahedral Al-Mn and Al-(MnFeCr) alloys were studied by neutron diffraction with scattering vectors up to 16 Å-1. The three partial pair distribution functions (PPDF) were obtained and the actual isomorphous substitution of the 03C3-FeCr mixture for Mn was confirmed. The PPDF for Mn-Mn indicates the existence of a manganese subnetwork rather similar to that found in the 03B1(AlMnSi) crystalline phase. In particular the shortest Mn-Mn distances were found at 4.47 and 4.97 A.

Short range order in Al–Fe–Nb, Al–Fe–Ce and Al–Ni–Ce metallic glasses

“…The results obtained in the present work agree with previous results on the total structure factor S Tot (Q) obtained on Al 90 Fe 5 Ce 5 [17,18], Al 85 Ni 10 Ce 5 [19,20] 3 and in Al 90 Ni 5 Ce 5 samples [20]. Similar XRD results were also obtained by Zhang et al [6] that compare Al-Fe and Al-Fe-Ce samples both in liquid and amorphous solid at different temperatures.…”

“…In Al-Ni-Nd samples studied by neutron diffraction [21], the S Tot (Q) function has a prepeak near 1.5 Å −1 and a main peak asymmetric with two contribution near 2.66 Å −1 and 3.06 Å −1 that agree with our results. Similar behavior was also found for Al-(Fe-Ni)-Si amorphous samples [2,3] though the less pronounced asymmetry of the main peak reported when Fe is replaced by Ni in that amorphous S Tot (Q) is not observed in Al-(Fe/Ni)-(Ce/Nb) samples in the 3 The results presented in Fig. 1 can be compared with Fig.…”

“…At least two characteristics related to these alloys have been considered in the present study. One characteristic is related to the effect of the transition metals (TM) in the solid and liquid Al-based systems, which have different local order depending on the TM contained in the alloy (mainly tetrahedral and icosahedral orders), as was previously reported [2][3][4][5][6][7][8]. Medium short range order is present in these alloys and was related to a strong heteroatomic interaction which can be related to a certain covalent character of the atomic bonds (which should be varying according to the TM electronic structure).…”

Aperiodic crystals and superspace concepts

“…A number of techniques have been developed to help structure determination. Here we may mention the contrastvariation method (Dubois & Janot, 1987) and the direct method adapted to aperiodic crystals (Hao et al, 1987). In recent years a number of additional techniques have been developed, such as the maximum-entropy method (Haibach & Steurer, 1996;Weber & Yamamoto, 1997;van Smaalen et al, 2003) and the charge-flipping method (Oszlá nyi & Sü to , 2004;Palatinus, 2013).…”

Derivation of the proper basis of quasicrystals

“…Several powerful structure solution techniques as well as refinement programs have been developed. [2][3][4][5][6] All promising techniques use the n-D embedding approach 7,8 to recover the phases. Up to now no unique method for choosing the n-D unit cell could be derived.…”