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Lithium Mobility in the Stannides Li2CuSn2 and Li2AgSn2


  • Dedicated to Professor Wolfgang Bensch on the Occasion of His 60th Birthday


The stannides Li2CuSn2 and Li2AgSn2 were synthesized by induction-melting (or in a muffle furnace) of the elements in sealed niobium ampoules. The new phases were characterized by powder X-ray diffraction. The structures of both stannides were investigated by X-ray diffraction on single crystals: Li2AuSn2 type, I41/amd, a = 442.6(1), c = 1940.9(8) pm, wR2 = 0.0742, 310 F2 values for Li2CuSn2 and a = 456.33(9) c = 2018.2(6) pm, wR2 = 0.0626, 339 F2 values for Li2AgSn2 with 10 variables for each refinement. The transition metal (T) atoms have tetrahedral tin coordination. The TSn4 tetrahedra are condensed via common corners forming layers that are further condensed by Sn–Sn bonding, leading to three-dimensional [CuSn2] and [AgSn2] networks which leave distorted hexagonal channels for the lithium atoms. The lithium ions show considerable mobility, with activation energies of 0.29 and 0.47 eV extracted from variable temperature 7Li solid state NMR spectra. 119Sn Mössbauer spectra at 78 K show signals at isomer shifts of δ = 2.13(1) mm s–1 for Li2CuSn2 and δ = 2.07(1) mm s–1 for Li2AgSn2. The signals show electric quadrupolar splitting because of the non spherical environment of the tin nuclei. A minor impurity of β-Sn could be identified in both spectra.

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