Structure and Ionic-Transport Properties of Lithium-Containing Garnets Li3Ln3Te2O12 (Ln = Y, Pr, Nd, Sm−Lu)

Lithium-containing compounds of the formula Li3Ln3Te2O12 (Ln = Y, Pr, Nd, Sm−Lu) have been prepared by solid-state ceramic methods at temperatures up to 900 °C. Rietveld refinement against X-ray and neutron powder diffraction data show that these phases adopt the garnet structure (space group Ia3̄d) with lattice parameters in the range 12.15970(14) Å (Li3Lu3Te2O12) to 12.61596(7) Å (Li3Pr3Te2O12). The Ln3+ 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 °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 σ ≈ 1 × 10-5 S cm-1 at 600 °C.