Darstellung und Kristallstrukturen vonLn2Al3Si2 undLn2AlSi2 (Ln: Y, Tb-Lu)

Abstract

Durch Erhitzen von Elementgemengen mit einer der jeweiligen Formel entsprechenden Zusammensetzung wurden acht neue ternäre Aluminiumsilicide dargestellt und ihre Kristallstrukturen mit Einkristallen röntgenographisch bestimmt. Tb2Al3Si2 (a = 10,197(2), b = 4,045(1), c = 6,614(2) Å, β = 101,11(2)°) und Dy2Al3Si2 (a = 10,144(6), b = 4,028(3), c = 6,580(6) Å, β = 101,04(6)°) kristallisieren im Y2Al3Si2‐Typ (C2/m; Z = 2), der von gewellten Al,Si‐Schichten geprägt wird, die über weitere Al‐Atome mittels linearer Si–Al–Si‐Bindungen miteinander verknüpft sind. Dadurch entstehen entlang [010] Kanäle, in denen sich die Seltenerdmetall‐Atome befinden. Die Silicide Ln2AlSi2 mit Ln = Y (a = 8,663(2), b = 5,748(1), c = 4,050(1) Å), Ho (a = 8,578(2), b = 5,732(1), c = 4,022(1) Å), Er (a = 8,529(2), b = 5,719(2), c = 4,011(1) Å), Tm (a = 8,454(5), b = 5,737(2), c = 3,984(2) Å) und Lu (a = 8,416(2), b = 5,662(2), c = 4,001(1) Å) haben eine zum W2CoB2‐Typ (Immm; Z = 2) analoge Atomanordnung, während Yb2AlSi2 (a = 6,765(2), c = 4,226(1) Å; P4/mbm; Z = 2) eine geordnete U3Si2‐Besetzungsvariante bildet. In allen Verbindungen wird Silicium von trigonalen Metallatomprismen umgeben, durch deren Flächenverknüpfung Si2‐Hanteln zustande kommen, in denen die Si–Si‐Abstände (2,37–2,42 Å) einer Einfachbindung entsprechen.

Intermetallic compounds in the M–Cu–Sn systems with M=Eu, Sr, Ba

“…All authors agree in observing the almost perfect phase purity on the chemical composition 1:9:4 and an ordered crystal structure for this phase. Regarding the distortion on going from the cubic model to the tetragonal one, it can be roughly measured by the deviation of the lattice parameters ratio from the ideal value c/a ¼ O2 ¼ [35], CeFe 9 Si 4 [42], MCo 9 Si 4 (M ¼ La [43], Pr [41], Nd [41], Sm [44], Tb [45]), CeCo 9 Ge 4 [46], LaNi 9 Si 4 and CeNi 9 Si 4 [37], SrCu 9 Si 4 , BaCu 9 Si 4 , SrCu 9 Ge 4 and BaCu 9 Ge 4 [47], MCu 9 Sn 4 (M ¼ Nd [17], Eu [12], Yb [5], Ca [9]). …”

Eleven new compounds in the RE–Cd–Ge systems (RE=Pr, Nd, Sm, Gd–Yb; Y): Crystal chemistry of the RE2CdGe2 series

“…220.15 (14) 241.77 (9) 236.0 (2) 229.79 (15) 225.33 (9) 221.88 (7) 219.66 (3) 216.04 (12) 214.48 (13) 212.94 (9) 214.65 (16) …”

“…Among these, the rareearth metal (RE) containing phases are abundant and can be grouped into several large RE 2 MX 2 classes, where the most commonly seen M-elements are Mg, In, Sn and Pb (main-group), or Cd; the X-elements are typically late transition metals such as Cu, Ni, Au, Pd, Pt, and Rh. In some cases (including the archetype), 'X' can be a non-metallic element -Si or Ge -and several series such as RE 2 MgGe 2 [3,4], RE 2 InGe 2 [5][6][7], RE 2 MgSi 2 [8], RE 2 AlSi 2 [9], and RE 2 AlGe 2 [10] have already been identified. Having studied some of the RE 2 InGe 2 compounds in our own laboratory [5], and having considered the fact that Cd and In are frequently found to form RE 2 InX 2 and RE 2 CdX 2 with the same transition metals, we set out to investigate the possibility to synthesize the up till now unknown RE 2 CdGe 2 phases.…”

Microstructure evolution and modification mechanism of the ytterbium modified Al–7.5%Si–0.45%Mg alloys

“…In addition, other potential particles formed in the alloys are YbAl 3 and Yb 2 AlSi 2 . The lattice mismatch of all the particles with silicon is too large to be the ideal nucleation site of silicon [38,39]. Therefore, the Yb-containing phases cannot be taken as nucleation sites of eutectic silicon because of the lattice misfit, which is consistent with the results of cooling curves given in Fig.…”