Influence of Cation Vacancies on Li Conductivity of La_1/2Li_1/2-2x Sr _x TiO₃ Perovskites (0 < x ≤ 0.25): The Role of Nominal and Effective Vacancies.

ABSTRACT: 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.

SUBMITTER: Bucheli W 

PROVIDER: S-EPMC10015983 | biostudies-literature | 2023 Mar

REPOSITORIES: biostudies-literature