Raman analysis and crystal structure of polycrystalline LiNi 1−x Co x PO 4 ( x = 0–0.5)

Polycrystalline orthophosphates LiNi1−xCoxPO4 (x = 0, 0.1, 0.2, 0.3, 0.4, and 0.5) have been prepared by the glycerol-nitrate synthesis method and used to study by the scanning electron microscopy, X-ray fluorescence analysis, X-rays diffraction and Raman scattering. All the LiNi1−xCoxPO4 polycrystalline samples contain particles having average crystallite size of less than 10 μm. According to X-ray fluorescence analysis the cobalt content in the LiNi1−xCoxPO4 samples does not exceed 1 at% comparing to a nominal concentration. In LiNi1−xCoxPO4 (x = 0–0.5) doping with cobalt at the nickel position leads to the increase in lattice constants of the olivine crystal structure (Pnma space group). The deformation vibrations in the LiNi1−xCoxPO4 crystals were observed in two types of vibrations of PO4 deformations such as ν2 (437.7 cm−1) and ν4 (582.0 cm−1, 591.1 cm−1, and 641.2 cm−1). Two peaks observed around 400–500 cm−1 range correspond to NiO6 or CoO6 and PO4 bending (ν2) deformation. Peaks observed around 585 cm−1 and 635 cm−1, correspond to LiO6 and PO4 bending (ν4) deformation, respectively. As the concentration of dopant (Co ions) increases, the Ag mode is gradually shifting toward higher wavenumber (949–950 cm−1). Changes in the wavenumber and intensity of the peak corresponding to the dopant element reveal that the dopant ions are occupying corresponding host lattice positions. The P–O3 bond length increased up to x = 0.2 and then decreased without a noticeable change in the crystal structure.