Electronic structure, physical properties and ionic mobility of LiAg2Sn

Wu ZY, Hoffmann RD, Johrendt D, Mosel BD, Eckert H, Pöttgen R

Abstract

The stannide LiAg2Sn was synthesized from the elements by reaction in a sealed tantalum tube in a resistance furnace. LiAg2Sn crystallizes with a ternary ordered version of the cubic BiF3 structure, space group Fm (3) over barm: a=659.2(2) pm, wR2=0.0450, 69 F-2 values, 5 variables. The silver and tin atoms form an antifluorite structure of composition Ag2Sn (285 pm Ag-Sn) in which the lithium atoms fill octahedral voids. Electronic structure calculations reveal weak Ag-Ag and strong Ag-Sn bonding within the Ag2Sn substructure. LiAg2Sn is weakly Pauli paramagnetic and a good metallic conductor. Nevertheless, the modestly small Li-7 Knight shift is consistent with a nearly complete state of lithium ionization. The high local symmetry at the tin site is reflected by the absence of a nuclear electric quadrupolar splitting in the Sn-119 Mossbauer spectra and a small chemical shift anisotropy evident from Sn-119 solid state NMR. Static Li-7 solid state NMR spectra reveals motional narrowing effects above 300 K, consistent with lithium atomic mobility on the kHz timescale.