Synthesis, sintering, electrical properties, and sodium migration pathways of new lyonsite Na 2 Co 2 (MoO 4 )3

Abstract

A new double molybdate Na22Co22(MoO4)34)3 was synthesized via solid-state reaction and characterized by single-crystal X-ray diffraction (XRD). This compound is a new member of the lyonsite structure type. It crystallized in the orthorhombic system, space group Pnma with cell parameters aa = 5.272(2) Å, bb = 10.816(3) Å, and cc = 18.064(3) Å. The structure can be described as a three-dimensional framework with hexagonal tunnels in which the Na++ cations lie. 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 was used to reduce the particle size of the synthesized powder. Dense ceramics with a relative density of 78% were obtained by sintering at 853 K. The conductivity of the title compound was studied for different relative densities. The ionic conductivity at 723 K with an activation energy of 1.2 eV was 3.24 ×× 10−6−6 S cm−1−1. The bond valence sum map model is used to simulate the cation migration pathways in the anionic framework.