Li2TeO4: Structural characterization and ionic conductivity measurements of a new tellurate

Abstract

A new tellurate Li₂TeO₄ (Li₂TeO₄-LT) was synthesized via a conventional solid-state route from specific precursors, LiOH.H₂O and H₆TeO₆. The cell, initially identified as tetragonal from X-ray powder diffraction at room temperature, was finally found to be orthorhombic thanks to thermal X-ray powder diffraction. The space group, Pbcn, was determined with the help of electron diffraction while the structure was obtained from neutron powder diffraction (a = 5.0106(3), b = 11.5369(8) and c = 5.0057(4) Å. As the tellurate β-Na₂TeO₄, its structure is built from TeO₆ octahedra sharing edges forming thus infinite chains [TeO₄]_n²ⁿ⁻ parallel to the c axis. These chains are separated from each other by Li⁺ ions in octahedral coordination. Contrary to β-Na₂TeO₄^, Li₂TeO₄-LT does not capture CO₂ and presents a modest ionic conduction (300 °C, T = 1.8 10⁻⁸ S cm⁻¹), lower than the tetragonal Li₂TeO₄ variety (300 °C, ≈10⁻⁶ S.cm-¹). In addition, a complete solid solution Na_2-xLi_xTeO₄ was evidenced.