In this paper we report synthesis, conductivity and structural data for the novel tetragonal garnet-related system, Li7La3Sn2O12. Neutron diffraction data shows that the tetragonal distortion is related to ordering of Li in three sites within the structure to ensure no short Li-Li interactions. Consistent with the ordered nature of the Li ions, the conductivity is low, with a high activation energy. The results are relevant to related highly conducting cubic garnets, Li5+xLn3-xAxM2O12 (Ln=rare earth, A=alkaline earth; M=Nb, Ta, Sb), showing how a high Li content can be accommodated by Li ordering within the garnet structure, supporting previous suggestions by Cussen for the cubic garnets, who proposed the presence of local ordering/clustering of Li in tetrahedral and "octahedral" sites to limit unfavourable short Li-Li interactions.

No abstract

Nanoscale inhomogeneity in La 1−x Sr x CoO 3 has been investigated in single-crystal samples for 0.05Յ x Յ 0.30 using 139 La and 59 Co NMR to probe local magnetization. In contrast to polycrystalline samples, single crystals exhibit ferromagnetism only above the metal-insulator critical concentration x C = 0.17. However, over the entire doping range, the single crystals exhibit an unusually broad and asymmetric distribution of hyperfine fields, evidencing ͑local͒ spin-polaron formation that persists to temperatures as high as 200 K, well above the glass transition reported previously from bulk magnetization. Above x C the asymmetry decreases rapidly with increasing doping as polarons overlap to give rise to long-range ferromagnetism. A modified phase diagram is presented. The key features of the data are reproduced by a simple model in which Sr dopants trigger spinpolaron formation, a physical picture first proposed by de Gennes ͓Phys. Rev. 118, 141 ͑1960͔͒.