On the Influence of the Vacancy Distribution on the Structure and Ionic Conductivity of A-Site-Deficient LixSrxLa2/3–xTiO3 Perovskites

Influence of Cation Vacancies on Li Conductivity of La1/2Li1/2-2x Sr x TiO3 Perovskites (0 < x ≤ 0.25): The Role of Nominal and Effective Vacancies

The Li_1/2-2x Sr _x La_1/2TiO₃ series (0 ≤ x ≤ 0.25) is investigated with X-ray diffraction, nuclear magnetic resonance, and impedance spectroscopy techniques. The substitution of two Li⁺ by one Sr²⁺ in Li_1/2La_1/2TiO₃ perovskite generates cation vacancies that, when ordered in alternating planes along the c-axis, confer a two-dimensional character to Li mobility. In previous works, it was shown that Li⁺ ions partially occupy the center of the six faces of the cubic perovskite, resulting in the associated A-sites to participate like a vacancy in the definition of the percolation vacancy threshold. The results obtained in the Li_1/2-2x Sr _x La_1/2TiO₃ series are compared with those obtained in the Li_3x La_2/3-x TiO₃ series, and other Sr-doped solid solutions (Li_1/2-x Sr_2x La_1/2-x TiO₃ and Li _x Sr _x La_2/3-x TiO₃), to highlight the importance of the effective vacancies with respect to the nominal ones in conductivity. The analysis of four series, belonging to the ternary SrTiO₃-La_2/3TiO₃-Li₂TiO₃ phase diagram, permits a better understanding of the ionic conduction mechanism in perovskites. The results show that the vacancy percolation model is more adequate to explain Li conductivity than the conventional hopping probability model. In the analyzed series, Li conductivity is maximum when a small amount of Sr is incorporated into the pseudo-cubic La_1/2Li_1/2TiO₃ end member, while it decreases as the amount of strontium increases.

Gallium-Doped Li7La3Zr2O12 Garnet-Type Electrolytes with High Lithium-Ion Conductivity

Owing to their high conductivity, crystalline Li_7-3xGa_xLa₃Zr₂O₁₂ garnets are promising electrolytes for all-solid-state lithium-ion batteries. Herein, the influence of Ga doping on the phase, lithium-ion distribution, and conductivity of Li_7-3xGa_xLa₃Zr₂O₁₂ garnets is investigated, with the determined concentration and mobility of lithium ions shedding light on the origin of the high conductivity of Li_7-3xGa_xLa₃Zr₂O₁₂. When the Ga concentration exceeds 0.20 Ga per formula unit, the garnet-type material is found to assume a cubic structure, but lower Ga concentrations result in the coexistence of cubic and tetragonal phases. Most lithium within Li_7-3xGa_xLa₃Zr₂O₁₂ is found to reside at the octahedral 96h site, away from the central octahedral 48g site, while the remaining lithium resides at the tetrahedral 24d site. Such kind of lithium distribution leads to high lithium-ion mobility, which is the origin of the high conductivity; the highest lithium-ion conductivity of 1.46 mS/cm at 25 °C is found to be achieved for Li_7-3xGa_xLa₃Zr₂O₁₂ at x = 0.25. Additionally, there are two lithium-ion migration pathways in the Li_7-3xGa_xLa₃Zr₂O₁₂ garnets: 96h-96h and 24d-96h-24d, but the lithium ions transporting through the 96h-96h pathway determine the overall conductivity.

Evidence for changes on the lithium conduction dimensionality of Li0.5−yNayLa0.5Nb2O6 (0 ≤ y ≤ 0.5) perovskites

Evidence for changes on Li conductivity dimensionality of Li_0.5−yNa_yLa_0.5Nb₂O₆ (y = 0–0.5) perovskite on increasing Na content.