Material Technology

The crystal structure and stability of K2NaAlH6

Sørby, M.H. , Brinks, H.W. , Fossdal, A. , Thorshaug, K. , Hauback, B.C.
Journal of alloys and compounds, Vol. 415, no. 1-2 (18 May 2006), 284-287
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The mixed alanate K2NaAlH6 has been synthesised by ball-milling a mixture of KH and NaAlH4 and subsequent annealing at 150 °C under a stabilizing hydrogen pressure. It takes a cubic ordered perovskite-type structure (space group F m over(3, ̄) m, a = 8.118(1) Å) where the ideal octahedral AlH63- units form a cubic close-packed structure with K+ in all tetrahedral sites and Na+ in all octahedral sites. K2NaAlH6 with 1 mol% TiF3 decompose quickly and reversibly with a flat plateau. Pressure-composition isotherms have been measured at five temperatures in the range 280-325 °C. The decomposition enthalpy and entropy were determined to 98(2) kJ/mol H2 and 150(4) J/(K mol H2) from the van't Hoff equation. © 2005 Elsevier B.V.
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