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摘要
The Li-rich ternary intermetallic compounds with the idealized end-member compositions Li3CuSn (CSD-427099) and Li6Cu2Sn3 (CSD-427100) were synthesized from the pure elements by induction melting in Ta crucibles and annealing at 400 degrees C. Both powder and single-crystal XRD investigations were performed. Li3CuSn crystallizes in space group P6/mmm [a = 4.5769(2), c = 8.461(2) angstrom; wR(2) = 0.073 for 180 unique F-2-values and 25 free variables]. All atoms are located along [00z], [1/3 2/3 z] and [2/3 1/3 z]; individual sites are arranged in layers parallel to (00.1). One site is fully, one partially occupied by Sn atoms. Fully but mixed occupation with Cu and Li atoms was found for one site. The remaining electron-density distribution resulting from the strong anisotropic displacement parallel to the c axis is considered in four further sites, which are mixed occupied with (Li, Cu,.), but modelled solely by Li atoms. The crystal structure exhibits analogies with that of Li2CuSn (F (4) over bar 3m); comparable layers occur parallel to {111} but the stacking sequence and packing density differs adopting cubic symmetry. In Li6Cu2Sn3 [space group R (3) over bar2/m, a = 4.5900(2), c = 30.910(6) angstrom; wR(2) = 0.039 for 253 unique F-2-values for 25 free variables] all atoms are arranged again at (00z), (1/3 2/3 z) and (2/3 1/3 z). Three sites are fully occupied (two by Sn atoms, a further one by Li atoms). Three additional positions are mixed occupied by Cu and Li atoms. The crystal structure is closely related to that of the binary phases Li 13 Sn 5 and Li 5 Sn 2; the substitution of Li by Cu atoms and vice versa is evident. The structural relationship to Li13Ag5Si6, which is permeable for Li ions, makes the title compound interesting as anode material in Li-ion batteries.
- 出版日期2016-2
