Phase transitions of the NASICON-type mixed phosphates LiM2(PO4)3 (M = Ti, Zr) and LiInNb(PO4)3

Structure and Vibrational Dynamics of NASICON-Type LiTi2(PO4)3

“…Among the NASICON-type materials, LiTi 2 (PO 4 ) 3 (LTP) is one of the most widely investigated. − Although its conductivity has been considered to be too low for practical applications, several studies have shown that it can be enhanced by the partial substitution of Ti 4+ ions by larger aliovalent cations modifying the bottlenecks of Li + conduction. − In contrast, other studies reported a substantial increase of the ionic conductivity of this compound by replacing Ti 4+ ions by smaller trivalent cations, resulting in the densification enhancement as well as in the increase of charge carriers and of lithium content at grain boundaries. − In both cases the increase in ionic conductivity is mainly due to the increase of charge carriers. In addition, to a minor extent the substituted trivalent cations influence the ionic transport by steric considerations and electronic polarizability .…”

Conducting solids

“…LiM(PO 4 ) 3 (M = Ti 2 , InNb, Zr 2 ) has been studied at elevated temperatures by lithium NMR, calorimetry techniques, impedance spectroscopy and X-ray diffraction. 73 The results indicate that as the temperature increases the lithium ions redistribute between the L1 and L2 sites with little effect on the structure of M = Ti 2 or InNb. In the zirconium samples, however, a slightly higher temperature for the phase transition is observed, which exhibits thermal hysteresis during heating and cooling.…”

Sites and Mobility of Lithium along the Li1+xTi2–xInx(PO4)3 (0 ≤ x ≤ 2) Series Deduced by XRD, NMR, and Impedance Spectroscopy

“…9−24 NaSICON materials can display R3̅ c, R3̅ , Ia3d, Pbca, P2 1 3, and P2 1 /n symmetry depending on the lattice distortions. 10 The NaSICON characteristics largely rely on the chemical composition, crystal structure, and unit-cell parameters. These factors are affected by the charge and radii of octahedral and tetrahedral cations.…”

“…21−23 In M = Ti 4+ , Ge 4+ phases, the structure only displays the rhombohedral symmetry (S.G. R3̅ c) in a large temperature interval. [10][11][12][13][14][15][16]24 Among NaSICON solid electrolytes, the lithium titanium phosphate LiTi 2 (PO 4 ) 3 (LTP) has attracted increasing interest because of its stability, low cost, raw, inherent safety and easy preparation.…”

“…The rhombohedral structure of Na super ionic conductors (NaSICON) LiM 2 (PO 4 ) 3 phases (S.G. R c ) can be described by three-dimensional networks, where PO 4 tetrahedra share oxygens with four MO 6 , and MO 6 octahedra share oxygens with six tetrahedra. − In this structure, two octahedra and three tetrahedra form structural M 2 (PO 4 ) 3 units denoted as “lantern units” (Figure a). In the conduction channels of NaSICON compounds, Li sites can occupy 6b Wyckoff (M1 sites) coordinated to six oxygens in trigonal antiprisms and 18e Wyckoff (M2 sites) coordinated to eight oxygens. − In some cases, Li ions can partially occupy midway M1/2 positions between M1 and M2 sites (36f Wyckoff sites).…”