Lithium Mobility in Li_1.2Ti_1.8R_0.2(PO₄)₃ Compounds (R = Al, Ga, Sc, In) as Followed by NMR and Impedance Spectroscopy

Abstract

Composition and lithium mobility have been analyzed in Li1+ x Ti (PO4)3 compounds (x = 0.2 and R3+ = Al3+, Ga3+, Sc3+, and In3+) by NMR and impedance spectroscopy. All of the compounds display the rhombohedral symmetry, and in all cases the trivalent cations are incorporated into the NASICON framework. From the analysis of the quadrupole constant (C Q) and spin−spin relaxation rate (T 2 -1) deduced from 7Li NMR spectra of Li1.2Ti1.8Al0.2(PO4)3, two regimes associated with local and long-range motions of lithium have been identified. From the analysis of the spin-lattice relaxation rate (T 1 -1) as a function of reciprocal temperature, the residence times of lithium at structural sites have been estimated and their dependence on temperature have been analyzed. Differences in activation energy deduced from NMR (0.22 eV) and conductivity (0.28 eV) measurements are discussed in terms of correlations in lithium motion that seem to decrease at increasing temperature.

On the influence of the cation vacancy on lithium conductivity of Li1+xRxTi2−x(PO4)3 Nasicon type materials

“…When titanium is partially substituted by trivalent R cations (R = Al, Ga, In, Fe, Sc, etc.) lithium conductivity increases in a significant way [12][13][14][15][16][17][18][19]. This increment has been ascribed to the creation of vacant Li1 sites at the intersection of conduction pathways.…”

X-ray photoelectron and broadband impedance spectroscopy of Li_1+4<i>x</i>Ti_2-<i>x</i>(PO₄)₃ solid electrolyte ceramics

“…It makes them attractive materials for investigations of the dynamic properties associated with peculiarities of ionic migration. According to [5,6], in some NASICON-type compounds Li + ions occupy two different energy sites in the lattice what is typical of most NASICON conductors, but the results of nuclear magnetic resonance investigation have shown only one lithium site in the lattice [7]. High ionic conductivity of the above-mentioned NASICON-type structure solid electrolyte compounds stimulate further investigation of their electrical properties in the broadband frequency and temperature ranges and relationship between compositions and transport properties of the materials.…”

XPS and ionic conductivity studies on Li1.3Al0.15Y0.15Ti1.7(PO4)3 ceramics

“…The biggest attention has been paid to the Li 1+x Al x Ti 2−x (PO 4 ) 3 system changing the stoichiometric factor x and conditions of ceramics' preparation. Conventional solid-state reaction [9,10], sol-gel process [11], ceramics' crystallization from glass [12], and ionic exchange Na + ⟶Li + in Na 1.3 Al 0.3 Ti 1.7 (PO 4 ) 3 [13] have been performed to obtain any of Li 1.2 Al 0.2 Ti 1.8 (PO 4 ) 3 , Li 1.3 Al 0.3 Ti 1.7 (PO 4 ) 3 , or Li 1.4 Al 0.4 Ti 1.6 (PO 4 ) 3 solid electrolytes. Different procedures of the preparation of solid electrolytes cause different grain boundary conductivity of the obtained ceramics; on the other hand, bulk conductivity can be changed by changing the cation M III and consequently the NASICON framework dimensions [14].…”

“…This material belongs to the rhombohedral crystal symmetry (space group R − 3c) which is typical for most NASICON conductors, but nuclear magnetic resonance investigation has showed only one lithium site [16]. In some NASICON-type structure compounds, Li ions occupy two different energy sites in the lattice [8,9]. In the present paper, we continue the study of solid electrolyte LiTi 2 (PO 4 ) 3 compound where Ti 4+ is partially substituted by Al +3 and Y +3 ions.…”