Interplay between magnetic ion and amorphous carbon in Na₃V₂(PO₄)₃/C nanocomposite

The crystal structure, magnetic properties and electrical properties of Na₃V₂(PO₄)₃/C nanocomposite were investigated using neutron and x-ray powder diffractometer, Raman spectroscopy, and experiments on ac magnetic susceptibility and ac impendence. Na₃V₂(PO₄)₃ has a trigonal structure with an R-3c space group and the carbon film coating has an amorphous phase at temperatures between 5 K and 300 K. An external magnetic field enlarged the lattice constant size parallel to the c-axis but had no effect on that parallel to the a-axis. Short-range magnetic correlation was observed below 220 K. A magnetic field of 1 mT was equivalent to a 1.4(2) K thermal effect the c-axis. The carbon film yielded Raman peaks associated with D₁-, D₃-, D₄-, and G-bands. The ac magnetic susceptibility curve is consistent with the Curie-Weiss law. The magnetic moment of V³⁺ and Curie temperature T_C of the sample were 2.91(6) μ_B/f.u. and 15(4) K, respectively. Ac impedance (Z) experiments demonstrated that the external magnetic field had no any effect on Z at 300 K. This investigation reveals a possibility of lattice and phonon control by the application of an external magnetic field. Its findings may be useful in developing lithium or sodium ion batteries.