Inherent instabilities of some W{sub 5}Si{sub 3}-type binary phases with large electropositive metal atoms: Six examples in the Ba-Pb, Ca-Sn-Mg,Cu,Zn, and La-Ga-Al,Zn systems

Journal Article · Sat Oct 15 00:00:00 EDT 2005 · Journal of Solid State Chemistry

DOI:https://doi.org/10.1016/j.jssc.2005.06.044· OSTI ID:20721714

Ganguli, Ashok K ^[1]; Gupta, Shalabh ^[1]; Zhao, J -T ^[1]; Alejandro Leon-Escamilla, E ^[1]; Corbett, John D ^[1]

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1. Ames Laboratory and Department of Chemistry, Iowa State University, Ames, IA 50011 (United States)

A particular pathology of certain W{sub 5}Si{sub 3}-type A{sub 5}B{sub 3} structures (I4/mcm) appears to arise because of unduly close approaches of the A1-type atoms on the cell faces at 12, 0, (14,34) that occur with the larger and more electropositive A and/or in the presence of smaller B atoms. A structure refinement of binary Ba{sub 4.81}Pb{sub 3} indicates such a marginal stability in that the Ba atoms in the facial Ba{sub 0.81} chains exhibit an extreme displacement ellipsoid along c-bar . Although Ca{sub 5}Sn{sub 3} and La{sub 5}Ga{sub 3} binaries are unknown in this structure type, five stable ternary derivatives of these have been synthesized via substitution reactions and characterized by single crystal X-ray diffraction means: Ca{sub 4}Sn{sub 3.223(4)}Mg{sub 0.777}, Ca{sub 4}Sn{sub 3}Cu{sub 1.30(4)}, Ca{sub 4.66(6)}Sn{sub 3}Zn{sub 0.704(4)}, La{sub 4.81(1)}Ga{sub 1.38(2)}Al{sub 1.62}, and La{sub 4.762(5)}Ga{sub 1.5(1)}Zn{sub 1.5}. Only the Ca-Sn-Zn phase exhibits lower symmetry, P4/mbm. The problematic A1 sites exhibit diverse changes in these, whereas the surrounding B2 tetrahedra are largely unaltered. The Ca-Sn results are, respectively: direct Mg/Sn substitution at the Ca1 site; mixed fractional distribution of the smaller Cu at two sites around the A1 position with an unresolved disorder; a pair of apparently independent modes, fractional Ca in the normal position and fractional Zn rectangles thereabout. The two La-Sn phases contain normal Ga,Al (Ga,Zn) tetrahedral chains with pairs of fractional disordered La atoms along 12, 0, z. Each can be rationalized in terms of a reasonable incommensurate structure. Electronic effects may also be operable.

• OSTI ID: 20721714
• Journal Information: Journal of Solid State Chemistry, Vol. 178, Issue 10; Other Information: DOI: 10.1016/j.jssc.2005.06.044; PII: S0022-4596(05)00298-7; Copyright (c) 2005 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved; Country of input: International Atomic Energy Agency (IAEA); ISSN 0022-4596
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
ALUMINIUM COMPOUNDS
BARIUM COMPOUNDS
CALCIUM COMPOUNDS
COPPER COMPOUNDS
DISTRIBUTION
GALLIUM COMPOUNDS
INSTABILITY
LANTHANUM COMPOUNDS
LEAD COMPOUNDS
MAGNESIUM COMPOUNDS
MONOCRYSTALS
STABILITY
SYMMETRY
TETRAGONAL LATTICES
TIN COMPOUNDS
TUNGSTEN SILICIDES
X-RAY DIFFRACTION
ZINC COMPOUNDS