Cation Miscibility and Lithium Mobility in NASICON Li1+xTi2–xScx(PO4)3 (0 ≤ x ≤ 0.5) Series: A Combined NMR and Impedance Study
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- 作者：Radhouene Kahlaoui ; Kamel ArbiIsabel Sobrados ; Ricardo Jimenez ; Jesus Sanz ; Riadh Ternane
- 刊名：Inorganic Chemistry
- 出版年：2017
- 出版时间：February 6, 2017
- 年：2017
- 卷：56
- 期：3
- 页码：1216-1224
- 全文大小：619K
- ISSN：1520-510X
文摘
Rhombohedral NASICON compounds with general formula Li1+xTi2–xScx(PO4)3 (0 ≤ x ≤ 0.5) have been prepared using a conventional solid-state reaction and characterized by X-ray diffraction (XRD), nuclear magnetic resonance (NMR), and impedance spectroscopy. The partial substitution of Ti4+ by Sc3+ and Li+ in pristine LiTi2(PO4)3 increases unit-cell dimensions and the number of charge carriers. In Sc-rich samples, the analysis of XRD data and 6Li/7Li, 31P, and 45Sc MAS NMR spectra confirms the presence of secondary LiScO2 and LiScP2O7 phases that reduce the amount of lithium incorporated in the NASICON phase. In samples with x < 0.3, electrostatic repulsions between Li ions located at M1 and M3 sites increase Li mobility. For x ≥ 0.3, ionic conductivity decreases because of secondary nonconducting phases formed at grain boundaries of the NASICON particles (core–shell structures). For x = 0.2, high bulk conductivity (2.5 × 10–3 S·cm–1) and low activation energy (Ea = 0.25 eV) measured at room temperature make Li1.2Ti1.8Sc0.2(PO4)3 one of the best lithium ionic conductors reported in the literature. In this material, the vacancy arrangement enhances Li conductivity.