Mn<sub>2</sub>TeO<sub>6</sub>: a Distorted Inverse Trirutile Structure

Inverse trirutile Mn<sub>2</sub>TeO<sub>6</sub> was investigated using in situ neutron and X-ray powder diffraction between 700 °C and room temperature. When the temperature was decreased, a structural phase transition was observed around 400 °C, from a tetragonal (<i>P</i>4<sub>2</sub>/<i>mnm</i>) to a monoclinic phase (<i>P</i>2<sub>1</sub>/<i>c</i>), involving a doubling of the cell parameter along <i>b</i>. This complex monoclinic structure has been solved by combining electron, neutron, and synchrotron powder diffraction techniques at room temperature. It can be described as a distorted superstructure of the inverse trirutile structure, in which compressed and elongated MnO<sub>6</sub> octahedra alternate with more regular TeO<sub>6</sub> octahedra, forming a herringbone-like pattern. Rietveld refinements, carried out with symmetry-adapted modes, show that the structural transition, arguably of Jahn–Teller origin, is driven by a single primary mode.