Structure and electrical properties of AM(PO₃)₄: A = Li, Na and M = Ce and Pr

In this manuscript, preparation, crystal structure and electrical properties of two types of A(I)M(III)(PO3)(4) meta-phosphates, namely LiCe(PO3)(4) and LiPr(PO3)(4) (monoclinic, C2/c), and NaCe(PO3)(4) (monoclinic, P2(1)/n) have been reported. All the compounds were prepared by conventional solid-state reaction and characterized by powder X-ray diffraction. The electrical properties of these materials were studied by impedance spectroscopy. The dc -conductivity (sigma(dc)) of all compounds show similar increasing trend with temperature and is attributed mainly to the alkali metal ion diffusion. However, a discontinuity in the temperature dependent sigma(dc) is observed at higher temperature in all of them. The activation energy (eV) for alkali ion conductivity in LiCe(PO3)(4), LiPr (PO3)(4) and NaCe(PO3)(4) respectively, is 1.14, 1.18 and 0.84, up to certain temperature (similar to 973K), and increases to 1.31, 1.35 and 1.51 at higher temperature. The analysis of ac-conductivity and modulus spectra indicated a correlated movement of ions in the structure. It is observed that structure and electrical properties of these metaphosphates are dependent more on the nature and ionic radii of the alkali ions than the rare-earth ions.