Ionic conductivity of Li_xLa_<10-x>(SiO_4)_6O_<3-x> sinters

概要

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A series of Li_2O-La_2O_3-SiO_2 sinters were prepared with the various ratios of the associated elements, Li: La: Si = x: (10-x): 6, and their ionic conductivities were examined. All the sinters were mainly composed of the apatite-type Li_xLa_<10-x>(SiO_4)_6O_<3-x> crystalline phases but sub-phases were produced in some cases. The lattice parameters of the main phase decreased with an increase in the Li-content, x, up to x = 2.0 and became constant above x = 2.0, indicating that La 4f-site was partially replaced by Li up to the maximum of x = 2.0. The conductivity of the sinters gradually increased with an increase in x to 1.5, but it suddenly dropped down at x = 2.0 and increased again by a further increase in x. The XRD and ^<29>Si-NMR results suggested that the first conductivity increase was due to the decrease in the content of the La_2SiO_5 sub-phase with the Li replacement. Furthermore, the ^7Li-NMR measurements gave evidence that lithium silicate sub-phase was formed at above x = 2 in the grain-boundary of the crystalline phase as a high Li-ionic conducting phase. The Nernst's EMF response of the O_2 and CO_2 concentration cells suggested that the main ionic carriers were oxide ion at x < 2.0 and lithium ion at x ≥ 2.
社団法人日本セラミックス協会の論文
2008-07-01