Structural Factors That Enhance Lithium Mobility in Fast-Ion Li_1+xTi_2–xAl_x(PO₄)₃ (0 ≤ x ≤ 0.4) Conductors Investigated by Neutron Diffraction in the Temperature Range 100–500 K

Abstract

Structural features responsible for lithium conductivity in Li 1+x Ti 2−x Al x (PO 4 ) 3 (x = 0, 0.2, and 0.4) samples have been investigated by Rietveld analysis of high-resolution neutron diffraction (ND) patterns. From structural analysis, variation of the Li site occupancies and atomic thermal factors have been deduced as a function of aluminum doping in the temperature range 100−500 K. Fourier map differences deduced from ND patterns revealed that Li ions occupy M1 sites and, to a lower extent, M3 sites, disposed around ternary axes. The occupation of M1 sites by Li ions is responsible for the preferential expansion of the rhombohedral R3̅ c unit cell along the c axis with temperature. The occupation of less symmetric M3 sites decreases electrostatic repulsions among Li cations, favoring ion conductivity in Li 1+x Ti 2−x Al x (PO 4 ) 3 compounds. The variations detected on long-range lithium motions have been related to variations of the oxygen thermal factors with temperature. The information deduced by ND explains two lithium motion regimes deduced previously by 7 Li NMR and impedance spectroscopy.Article pubs.acs.org/IC

Microwave-assisted reactive sintering and lithium ion conductivity of Li1.3Al0.3Ti1.7(PO4)3 solid electrolyte

“…It has been unambiguously demonstrated recently that lithium ion conduction involves both sites according to a M1-M3-M3-M1 zig zag pathway (Fig. 4b) [33,34]. The corresponding activation energy, calculated from data obtained by the maximum-entropy method (MEM), is 0.30 eV (maximum entropy method), which is equal to the value obtained in this work below 135 °C.…”

“…Recent studies demonstrate that the Li-ion bulk conductivity of LATP is intrinsic in nature and is mainly based on the incorporation of the additional Li-ions as highly mobile charge carriers within the fast-diffusion pathways in the R-3c NASICON structure [33]. In this structure, lithium ions are located in two positions, namely M1 (6b) and M3 (36f), respectively (see [25] for more details on the LATP crystal structure).…”

Identifying Li+ ion transport properties of aluminum doped lithium titanium phosphate solid electrolyte at wide temperature range

“…For x = 0.05, x = 0.1 and x = 0.2, the measured bulk conductivities were 2.3 × 10 − 3 S cm −1 , 2.2 × 10 −3 S cm −1 and 5.1 × 10 −3 S cm −1 , respectively. The related activation energy decreased from 0.33 eV to 0.30 and 0.28 eV respectively [8,9]. These results seem to support that the bulk conductivity of LTP can be increased after Al-doping.…”

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.…”