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Structurally Complex Cobalt Intermetallics Grown from Liquid Aluminum:  Co19Al45Si10-x (x = 0.13) and Co5Al14Si2

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posted on 2006-07-10, 00:00 authored by Xiuni Wu, Susan Latturner, Mercouri G. Kanatzidis
The cobalt aluminum silicides Co19Al45Si10-x (x = 0.13) and Co5Al14Si2 were synthesized in liquid aluminum and characterized by single-crystal X-ray diffraction. Co19Al45Si10-x (x = 0.13) crystallizes in the monoclinic space group C2/c with lattice parameters a = 19.991(2) Å, b = 19.143(2) Å, c = 12.8137(15) Å, β = 123.583(2)°. Co5Al14Si2 adopts the orthorhombic space group Pnma with cell parameters a = 13.8948(19) Å, b = 23.039(3) Å, c = 7.3397(10) Å. Both structures are exceptionally complex with the Co2Si2 rhombus being a common building motif. The coordination environments of cobalt atoms resemble those of the transition metals in typical quasi-crystal approximants. Co5Al14Si2 shows oxidation resistance in air up to 1000 °C by forming a dense-packed Al2O3 layer on the surface of the crystal.

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