The crystal structure of lithium tantalum oxyfluoride LiTaO2F2

A structural analysis of lithium tantalum oxyfluoride LiTaO2F2 has been carried out by means of single-crystal diffraction methods. The symmetry is tetragonal, space group I4/mmm, with a cell having the dimensions : a = 3.903 ± 0.003, c = 25.380 ± 0.008 A and containing five formula units. The structure was solved by Patterson and Fourier techniques and was refined by full-matrix least squares to an R value of 0.056. The structure consist of infinite ReO3 type blocks three units-cells thick stacked perpendicularly to the c axis and shifted along the [110] direction with respect to each other. These blocks are connected together by the lithium atoms in a squarepyramidal coordination.