The formation mechanism and structural characterization of the mixed transition-metal complex hydride Mg2(FeH6)0.5(CoH5)0.5 obtained by reactive milling.
Mg2(Fe0.5Co0.5) elemental powder mixtures were processed by reactive ball milling in a H2 (orD2) atmosphere at about 50 bar. The changes of pressure were monitored during milling and hydrogen absorption was detected within the first 10 h of milling. X-ray and neutron powder diffraction analysis, followed by Rietveld refinement, suggests an almost complete conversion of the starting metals into the quaternary hydride Mg2(FeH6)0.5(CoH5)0.5. The latter has a cubic K2PtCl6-type structure (space group Fm3m) with a cell parameter a approximately 6.42 A degrees. Fe and Co atoms are disorderly distributed in the 4a position. Hydrogen desorption upon heating was investigated by both in situ x-ray diffraction and temperature programmed desorption analysis.Hydrogen is released in a one-step desorption reaction at temperatures between 500 and 600 K,with Mg and a FeCo solid solution as desorption products. Finally, Mg2(FeH6)0.5(CoH5)0.5 was also synthesized by ball milling equi-molar mixtures of Mg2FeH6 and Mg2CoH5 in Ar.
Physics Department, Institute for Energy Technology, PO Box 40, NO-2027 Kjeller, Norway.
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D003460:Crystallization / Q000379:methods*; D006859:Hydrogen / Q000737:chemistry*; D046911:Macromolecular Substances / Q000737:chemistry; D008420:Manufactured Materials / Q000032:analysis*; D008422:Materials Testing; D008968:Molecular Conformation; D049329:Nanostructures / Q000737:chemistry* / Q000648:ultrastructure*; D036103:Nanotechnology / Q000379:methods*; D010316:Particle Size; D013499:Surface Properties; D028561:Transition Elements / Q000737:chemistry*
D046911:Macromolecular Substances; D028561:Transition Elements; D006859:Hydrogen