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

A new tellurate Li 2 TeO 4 (Li 2 TeO 4 -LT) was synthesized via a conventional solid-state route from specific precursors, LiOH.H 2 O and H 6 TeO 6 . 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-Na 2 TeO 4 , its structure is built from TeO 6 octahedra sharing edges forming thus infinite chains [TeO 4 ] n 2n− parallel to the c axis. These chains are separated from each other by Li + ions in octahedral coordination. Contrary to β-Na 2 TeO 4 , Li 2 TeO 4 -LT does not capture CO 2 and presents a modest ionic conduction (300 °C, T = 1.8 10 −8 S cm −1 ), lower than the tetragonal Li 2 TeO 4 variety (300 °C, ≈10 −6 S.cm- 1 ). In addition, a complete solid solution Na 2-x Li x TeO 4 was evidenced. • Li 2 TeO 4 : a new ionic conductor tellurate. • The crystal system could only be found using the thermal X-ray diffraction. • Essential role of the TEM technique in the determination of the space group.