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Novel Tin Structure Motives in Superconducting BaSn 5 – The Role of Lone Pairs in Intermetallic Compounds [1]
Author(s) -
Fässler Thomas F.,
Hoffmann Stefan,
Kronseder Christian
Publication year - 2001
Publication title -
zeitschrift für anorganische und allgemeine chemie
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.354
H-Index - 66
eISSN - 1521-3749
pISSN - 0044-2313
DOI - 10.1002/1521-3749(200111)627:11<2486::aid-zaac2486>3.0.co;2-i
Subject(s) - intermetallic , tin , superconductivity , lone pair , condensed matter physics , crystallography , tetragonal crystal system , electronic band structure , electronic structure , materials science , van hove singularity , phase (matter) , atom (system on chip) , chemistry , crystal structure , fermi level , electron , physics , metallurgy , molecule , alloy , quantum mechanics , computer science , embedded system , organic chemistry
BaSn 5 is the tin richest phase in the system Ba/Sn and is obtained by stoichiometric combination of the elements. The compound peritecticly decomposes under formation of BaSn 3 and a Sn–Ba melt at 430 °C. The structure shows a novel structure motive in tin chemistry. Tin atoms are arranged in graphite‐like layers (honeycombs). Two such layers form hexagonal prisms which are centered by Sn. Consequently the central tin atom has the unusual coordination number 12. The two‐dimensional tin slabs which consist of two 3 6 and one 6 3 nets of Sn atoms are separated by 6 3 nets of Ba atoms with Ba above the center of each tin hexagon. The structure of BaSn 5 can be rationalized as a variante of AlB 2 and thus also of the superconducting MgB 2 . Temperature dependent magnetic susceptibility measurements show that BaSn 5 is superconducting with T c = 4.4 K. Reinvestigation of the magnetism of the Ba richer phase BaSn 3 reveals for this compound a T c of 2.4 K. LMTO band structure and density of states calculations verify the metallic behavior of BaSn 5 . The van Hove scenario of high‐temperature cuprate superconductors is discussed for this ‘classical' intermetallic superconductor. An analysis of the electronic structure with the help of fat‐band projections and the electron localization function (ELF) shows that the van Hove singularity in the DOS originates from non‐bonding (lone) electron pairs in the intermetallic phase BaSn 5 . The role of lone pairs in intermetallic phases is discussed with respect to superconducting properties.