Abstract
There is a great interest in gaining a deeper understanding of the lithium ion conductivity of Li-stuffed garnets that result from the substitution at either the La or M sites in Li5La3M2O12 (M = Nb, Ta), since these materials can be used as potential electrolytes in all solid-state batteries. Here, we investigate the effect of replacing Nb5+ with Gd3+ and stuffing two Li+ per Gd3+ in Li5La3Nb2O12 on the structure and ionic conductivity of the new family of garnet-type compounds with the nominal formula Li5+2xLa3Nb2-xGdxO12 (0 ≤ x ≤ 0.45). The samples were prepared via conventional solid-state synthesis in air at elevated temperatures. Powder X-ray diffraction studies confirmed the formation of the garnet-type structure for Li5+2xLa3Nb2-xGdxO12 (0 ≤ x ≤ 0.45). Elemental mapping obtained using energy dispersive X-ray analysis showed no evidence of a secondary phase being formed in Li5+2xLa3Nb2-xGdxO12 (0 ≤ x ≤ 0.45). Archimedes density measurements confirmed that the density of the samples with x ≤ 0.25 is not improved. The porosity of the samples with x ≥ 0.3 was found to be in the 8%-16% range. Among the samples investigated in this work, the x = 0.45 member of Li5+2xLa3Nb2-xGdxO12 showed the highest ionic conductivity of 1.91 × 10-5 S cm-1 at room temperature, which is an order of magnitude higher than that of the parent compound Li5La3Nb2O12. The activation energy of this material was calculated to be 0.38 eV at 25-225 °C and 0.28 eV at 225-325 °C. The change in the activation energy at the high temperature regime can be explained using the Li site occupation model in the garnet-type structure.
Original language | English |
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Pages (from-to) | 321-329 |
Number of pages | 9 |
Journal | Canadian Journal of Chemistry |
Volume | 94 |
Issue number | 4 |
DOIs | |
Publication status | Published - 2016 |
Keywords
- Conductivity
- Li-stuffed garnets
- LiLaNbGdO (0 ≤ x ≤ 0.45)
- Solid Li ion electrolytes