A new lithium chalcogenidotetrelate, denoted as LiChT phase, with the elemental combination Li/Sn/S was synthesized as solvent-free and solvent-containing salts. We present and discuss syntheses, crystal structures, spectroscopic and thermal properties of the phases, as well as the Li + ion conductivity of Li 4 SnS 4 , which is formally related to the thio-LISICON parent system Li 4 GeS 4 , and thus represents the first member of a new thiostannate-LISICON family. The solvent-free title compound shows a very promising Li + ion conductivity of 7 × 10 −5 S·cm −1 at 20°C and 3 × 10S·cm −1 at 100°C, which is exceptionally high for a ternary compound. Activation energies for the lithium ion transport measured via impedance spectroscopy (0.41 eV) correlate reasonably well with the values (0.29 to 0.33 eV) deduced from ionic mobility studies by 7 Li solid-state NMR spectroscopy. NMR two-time correlation functions suggest the occurrence of an additional, geometrically more restricted, ultraslow-motional process down to 121 K.

No abstract

The structural aspects of the glass-to-crystal transition in the technologically important ion conducting glass ceramic system Li 1+x Al x Ge 2−x (PO 4 ) 3 (0 ≤ x ≤ 0.75) have been examined by complementary multinuclear solid state nuclear magnetic single and double-resonance experiments. In the crystalline state, the materials form solid solutions in the NASICON structure, with additional nanocrystalline AlPO 4 present at x values ≥0.5. Substitution of Al in the octahedral Ge sites results in a binomial distribution of multiple phosphate species, which differ in the number P−O−Al and P−O−Ge linkages and can be differentiated by 31 P double quantum NMR studies suggest that the AlO 6 coordination polyhedra are noticeably expanded compared to the GeO 6 sites in the NASICON-type LiGe 2 (PO 4 ) 3 (LGP) structure. While the glassy state is characterized by a significantly larger degree of disorder concerning the local coordination of germanium and aluminum, dipolar solid state NMR studies clearly indicate that their medium range structure is comparable to that in NASICON, indicating the dominance of P−O−Al and P−O−Ge over P− O−P and Al−O−Ge connectivities. ■ INTRODUCTIONThe rapid growth in global energy demand in the face of dwindling global resources has been stimulating increasing efforts toward the development of high energy and high power batteries based on both lithium ion 1 and solid oxide fuel cell (SOFC) 2 technologies. Both processes utilize fast ion transport in the solid state at ambient or elevated temperatures. During the past two decades a large number of crystalline and glassy fast ion conductors have been identified and thoroughly characterized, and excellent reviews on oxide and proton conductors for fuel cell applications, 3 as well as fast ion conductors for lithium batteries, are available.4−6 The highest lithium ion conductivities in the solid state are generally encountered in crystalline compounds with highly disordered cation sublattices, termed superionic crystals. On the other hand, ion conducting glasses are often preferred in practice as they do not suffer from grain boundary effects and form more homogeneous interfaces with the anode and cathode compartments of a solid state electrochemical cell. The favorable features of both the crystalline and the glassy state can be combined in an ideal way using ion conducting glass ceramics, and numerous promising systems presenting electrical conductivities in excess of 10 −3 (Ω·cm) −1 at room temperature have been developed. 7,8 One particularly attractive system is based on the crystallization of precursor glasses in the systems Li 2 O-MO 2 -Al 2 O 3 -P 2 O 5 (M = Ge, Ti). While the glasses themselves are poorly conducting, they crystallize in the NASICON structure, which features exceptionally high ionic conductivities.9−15 Their structure is derived from the phases MTi 2 (PO 4 ) 3 (M = Li, Na) and MGe 2 (PO 4 ) 3 , which feature octahedrally coordinated Ti 4+ and Ge 4+ cations linked through phosphate tetrahedra via corner sharing ...

No abstract