The Origin of Phase Transition and the Usual Evolutions of the Unit-Cell Constants of the NASICON Structures of the Solid Solution LiTi2 – xGex(PO4)3

• Published in: Physics of the solid state 2019, Vol.61 (12), p.2446-2450
• Main Author: Bounar, Nedjemeddine
• Format: Article
• Language: English
• Subjects: Composition; Germanium; Parameters; Phase Transitions; Photomicrographs; Physics; Physics and Astronomy; Solid solutions; Solid State Physics; Substitution reactions; Temperature; Unit cell; X ray powder diffraction
• ISSN: 1063-7834; 1090-6460
• DOI: 10.1134/S1063783419120072

Ge-doped LiTi 2 (PO 4 ) 3 has been synthesized by a conventional solid-state reaction. Compounds LiM (PO 4 ) 3 with LTP-type structure present a different behaviour depending on nature of M (IV) . For M (IV)  = Ti and Ge, the structure shows the space group R3c, whereas for M (IV) = Ge the space group is R3. Differences in behaviour of LiTi 2 (PO 4 ) 3 –LiGe 2 (PO 4 ) 3 solid solutions are discussed in relation to the composition. Their structures LiTi 2 –   x Ge x (PO 4 ) 3 (0 ≤ x < 2) were determined from X-ray powder diffraction method (XRD) using Rietveld analysis. A sharp change in the lattice parameter a is observed between the compositions with x = 1. The lattice parameter c increases as the Ge content increases in the whole range of composition. The space group R3c becomes R3 for the composition with x > 1. The SEM micrographs of the samples show relative porous microstructures due to the effect of the substitution.