Abstract:
In this article, the conductive and dielectric properties of polycrystal Na$_3$Sc$_2$(PO$_4$)$_3$, which has three polymorphic $\alpha$–, $\beta$–, $\gamma$– phases, are studied. The structural features of the $\alpha$–Na$_3$Sc$_2$(PO$_4$)$_3$ crystal, as well as dipole ordering and relaxation polarization in the $\alpha$ and $\beta$– phases, are refined. The occurrence of dipole ordering in the $\alpha$ phase and partial disordering in $\beta$–Na$_3$Sc$_2$(PO$_4$)$_3$, as well as high ionic conductivity in the $\beta$–, $\gamma$– phases of the Na$_3$Cr$_2$(PO$_4$)$_3$ crystal is due to phase transformations $\alpha$$\rightarrow $$\beta$, $\beta$$ \rightarrow$$\gamma$, resulting in structural changes of the rhombohedral crystal framework \{[M$_2$(PO$_4$)$_3$]$_{3-}$\}$_{3{\infty}}$. A model explaining the conductive and dielectric properties of Na$_3$Sc$_2$(PO$_4$)$_3$ is proposed.
