Fig. 1: NMR relaxation rates and spectra.
From: Interfacial lithiation of lithium aluminum titanium phosphate explored by 7Li NMR
Temperature evolution of the 7Li NMR spin-lattice relaxation rates (116 MHz, 20 kHz locking frequency) of (a) non-lithiated Li1.5Al0.5Ti1.7(PO4)3 and lithiated Li1.3+xAl0.3Ti1.7(PO4)3 [(a) x = 0.2, (b) x = 0.6, and (c) x = 1.3)]. The rates have been recorded in both the laboratory (R1) and rotating (R1ρ) frame of reference. In the latter case, we observe the transversal adjustment of the magnetization that is locked through a weak B1 field. As in the case of R1, this adjustment is driven through diffusive processes but sensitive to motional correlation rates in the kHz rather than the MHz regime. Upon lithiation, we observe a slight shift of the R1ρ(1/T) peaks towards lower temperature that is accompanied with a reduction in activation energy determining the low-T flank. For R1, an additional shallow peak emerges when x takes values equal or larger than 0.6 (b). The latter points to rapid localized Li+ exchange processes that are hardly seen in unlithiated LATP. Lines are to guide the eye. Values in eV refer to the activation energies corresponding to the linear parts of the curves. d to f; Variable-temperature 7Li (I = 3/2) NMR line shapes (116 MHz) of the same samples recorded under static conditions. For the samples with (d) x = 0.2 and (e) x = 0.6, central and satellite intensities, that is, the 90° singularities of the powder patterns, are seen (note the different scaling of the abscissae). f Increasing x to 1.3, causes the lines to be strongly affected by dipolar paramagnetic broadening because of the increasing number of Ti3+ centers formed.
