Structure and ionic-transport properties of lithium-containing garnets Li3Ln3Te2O12 (Ln = Y, Pr, Nd, Sm-Lu)

Lithium-containing compounds of the formula Li(3)Ln(3)Te(2)O(12) (Ln = Y, Pr, Nd, Sm-Lu) have been prepared by solid-state ceramic methods at temperatures up to 900 degrees C. Rietveld refinement against X-ray and neutron powder diffraction data show that these phases adopt the garnet structure (space group Ia (3) over bard) with lattice parameters in the range 12.15970(14) angstrom (Li3Lu3Te2O12) to 12.61596(7) angstrom (Li3Pr3Te2O12). The Ln(3+) and Te6+ cations occupy the 8-fold and octahedrally coordinated sites, and Li+ is accommodated exclusively in the tetrahedral sites commonly occupied in the garnet structure. Neutron diffraction data collected from Li3Nd3Te2O12 at 300 and 600 degrees C show that the lithium coordination does not change over this temperature range. Impedance spectroscopy measurements indicate that Li3Nd3Te2O12 shows minimal Li+ mobility with an activation energy of 1.22(15) eV, resulting in a maximum observed conductivity of sigma approximate to 1 x 10(-5) S cm(-1) at 600 degrees C.