Synthesis, sintering, electrical properties, and sodium migration pathways of new lyonsite $Na_2Co_2;{(MoO_4)}_3$

Abstract

A new double molybdate $Na_2Co_2;{(MoO_4)}_3$ was synthesized via solid-state reaction and characterized bysingle-crystal X-ray diffraction (XRD). This compound is a new member of the lyonsite structure type. It crystallized inthe orthorhombic system, space group Pnma with cell parameters a = 5.272(2) Å, b = 10.816(3) Å, and c = 18.064(3)Å. The structure can be described as a three-dimensional framework with hexagonal tunnels in which the Na + cationslie. The obtained structural model is supported by charge distribution analysis and bond valence sum validation tools.Fourier-transform infrared spectroscopy and scanning electron microscopy analyses were carried out. Ball milling wasused to reduce the particle size of the synthesized powder. Dense ceramics with a relative density of 78% were obtainedby sintering at 853 K. The conductivity of the title compound was studied for different relative densities. The ionicconductivity at 723 K with an activation energy of 1.2 eV was 3.24 × $10^{-6}$ S $cm^{-1}$. The bond valence sum map modelis used to simulate the cation migration pathways in the anionic framework.