Solid-State NMR Investigations on the Structure and Dynamics of the Ionic Conductor Li1+xAlxTi2–x(PO4)3 (0.0 ≤ x ≤ 1.0)

详细信息    查看全文

• 作者：C. Vinod Chandran ; Sylke Pristat ; Elena Witt ; Frank Tietz ; Paul Heitjans
• 刊名：Journal of Physical Chemistry C
• 出版年：2016
• 出版时间：April 28, 2016
• 年：2016
• 卷：120
• 期：16
• 页码：8436-8442
• 全文大小：370K
• 年卷期：0
• ISSN：1932-7455

文摘

The local structure and mobility of lithium ions of the NASICON-type ionic conductor Li_1+xAl_xTi_2–x(PO₄)₃ (with x = 0.0, 0.1, 0.2, 0.35, 0.5, 0.7 and 1.0), synthesized using conventional solid-state reaction route have been studied with solid-state nuclear magnetic resonance (NMR) techniques. ⁶Li, ⁷Li, ²⁷Al, and ³¹P solid-state NMR experiments have been employed to trace the structural changes with varying cation concentration. The structural evolution and the creation of new Al and P environments with changing cation contents were studied by magic-angle spinning (MAS) NMR measurements. ⁶Li MAS NMR and ²⁷Al triple-quantum MAS (3QMAS) show high-resolution spectra enabling site assignments and phase-purity inspections. The temperature dependences of ⁷Li NMR spin–lattice relaxation (SLR) rates for different compositions yield important information on the lithium ion mobility in the systems. Li ion jump rates, the activation energies, and the dimensionality of Li diffusion were deduced from the SLR experiments. A vacancy migration model has been proposed for the Li⁺ ionic diffusion process in pure-phase Li_1+xAl_xTi_2–x(PO₄)₃ prepared by solid-state reaction. Above a certain threshold value of x (0.5) additional phosphate phases appear that slows down diffusion. This phenomenon can be observed from ⁶Li exchange spectroscopy. The optimum cation concentration for maximum ionic mobility in the phase-pure Li_1+xAl_xTi_2–x(PO₄)₃ system can be read directly from the solid-state NMR results.