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 °C. Rietveld refinement against X-ray and neutron powder diffraction data show that these phases adopt the garnet structure (space group I a3̄ d ) with lattice parameters in the range 12.15970(14) Å (Li 3 Lu 3 Te 2 O 12 ) to 12.61596(7) Å (Li 3 Pr 3 Te 2 O 12 ). The Ln 3+ and Te 6+ 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 Li 3 Nd 3 Te 2 O 12 at 300 and 600 °C show that the lithium coordination does not change over this temperature range. Impedance spectroscopy measurements indicate that Li 3 Nd 3 Te 2 O 12 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.