Structure and electrical properties of Na-modificated spinel LiNi$_{0.5}$Mn$_{1.5}$O$_4$

The paper presents the results of X-ray diffraction analysis, microstructure and dielectric characteristics studies of solid solutions in the Li$_{1-x}$Na$_x$Ni$_{0.5}$Mn$_{1.5}$O$_4$ system. X-ray diffraction analysis showed that solid solutions in the Li$_{1-x}$Na$_x$Ni$_{0.5}$Mn$_{1.5}$O$_4$ system have a disordered structure of the Fd3m spinel type. The introduction of Na$^+$ into the system leads to the formation of NiO and LiMnO$_2$ impurity phases, the concentration of which increases with increasing Na$^+$ concentration. It is shown that the introduction of Na$^+$ into the system leads to a decrease in the cell parameter, which indicates its non-inclusion or limited inclusion in the LiNi$_{0.5}$Mn$_{1.5}$O$_4$ crystal lattice. Analysis of the dielectric spectral dependencies showed that there is no transition to the ferroelectric phase in Li$_{1-x}$Na$_x$Ni$_{0.5}$Mn$_{1.5}$O$_4$ solid solutions. The increase in electrical conductivity above 150 K is due to hopping conductivity.