Optical and dielectric properties of NaCoPO 4 in the three phases α, β and γ.

In this work, we are interested in the synthesis of monophosphate α-NaCoPO 4 , β-NaCoPO 4 and γ-NaCoPO 4 compounds by mechanochemical method and their characterization by X-ray powder diffraction patterns. These compounds are crystallized in the orthorhombic, hexagonal and monoclinic system, in Pnma , P 6 5 and P 2 1 / n space groups, respectively. The optical properties were measured by means of the UV-vis absorption spectrometry in order to deduce the absorption coefficient α and optical band gap E g . The calculated values of the indirect band gaps ( E gi ) for three samples were estimated at 4.71 eV, 4.63 eV and 3.8 for compounds α, β and γ, respectively. The Tauc model was used to determine the optical gap energy of the synthesized compounds. Then, the results of the dielectric proprieties measured by varying the frequency are described.