Spectroscopic investigations on vanthoffite ceramics partially doped with cobalt

In this present work, we have successfully synthesized highly pure phases of Na6Mg1-xCox (SO4)4 vanthoffite powder ceramics denoted as NMCoSx using the solid-state reaction method. Refinement of structural parameters confirmed that the Co2+ dopant can replace the magnesium in this structure with a slight increase of the lattice parameters. The spectroscopic studies by means of infrared (IR) and visible (Vis) spectroscopies revealed the vibrational mode of sulfate groups and verified the amount of cobalt inserted in the host lattice. Electrical conductivity was studied by impedance spectroscopy in the [553–733 K] temperature range and results show that the materials present a semiconductor ionic character and the conductivity increases when the Co2+ dopant content x increases. Results also show that at low temperatures, NMCoSx (x = 0.5) has the highest electrical conductivity representing a candidate that may be used as an electrode in sodium-ion batteries.