Premium
From V 8 Ga 36.9 Zn 4.1 and Cr 8 Ga 29.8 Zn 11.2 to Mn 8 Ga 27.4 Zn 13.6 : A Remarkable Onset of Zn‐Cluster Formation in an Intermetallic Framework
Author(s) -
Viklund Per,
Svensson Christer,
Hull Steve,
Simak Sergei I.,
Berastegui Pedro,
Häußermann Ulrich
Publication year - 2001
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/1521-3765(20011203)7:23<5143::aid-chem5143>3.0.co;2-p
Subject(s) - crystallography , intermetallic , ternary operation , fermi level , electron counting , neutron diffraction , cluster (spacecraft) , metal , materials science , formula unit , chemistry , crystal structure , electron , physics , alloy , metallurgy , quantum mechanics , computer science , programming language
Abstract The series of isotypic compounds V 8 Ga 41 → V 8 Ga 36.9 Zn 4.1 →Cr 8 Ga 29.8 Zn 11.2 → Mn 8 Ga 27.4 Zn 13.6 with the V 8 Ga 41 structure type (space group R $\bar 3$ , Z =3) was prepared and structurally characterised by X‐ray diffraction experiments (V 8 Ga 41 : a = 13.9351(5), c = 14.8828(12); V 8 Ga 36.9 Zn 4.1 : a =13.9244(7), c =14.8660(9); Cr 8 Ga 29.8 Zn 11.2 : a = 13.7153(5), c = 14.6872(9); Mn 8 Ga 27.4 Zn 13.6 : a = 13.6033(6), c =14.6058(16)). The site occupancies of the ternary compounds were refined from neutron powder‐diffraction data and exposed a startling segregation of Zn and Ga, which finally resulted in the formation of separated Zn 13 cluster entities—corresponding to almost ideal centred cuboctahedra or small pieces of fcc metal—‐in the Mn compound, which has the highest Zn content in the series. The homogeneity ranges of the underlying phases T 8 Ga 41− x Zn x were determined to be 0< x <4.1(3), 8.7(3)< x <11.2(3) and 13.6(4)< x <16.5(3) for T=V, Cr and Mn, respectively. The different ranges of composition of the phases reflect the requirement of an optimum electron concentration for a stable V 8 Ga 41 ‐type structure, which is in the narrow range between 159 and 165 electrons per formula unit. First‐principles electronic‐structure calculations could explain this fact by the occurrence of a pseudo gap in the density of states at which the Fermi level is put for this particular electron concentration. Furthermore the nature of the Zn/Ga segregation was revealed: T–Zn interactions were found to be considerably weaker than those for T–Ga. This places the Zn atoms as far as possible from the T atoms, thus leading to the formation of cuboctahedral Zn 13 entities.