Fluorination of La2−xSrxCuO4 (x = 0, 0.15, 0.3) and study on the crystal structures, magnetic properties of their fluorinated products

• Fluorination of La2−xSrxCuO4 (x = 0, 0.15, 0.3) by ZnF2 with few byproducts.
• Less of impurities are benefit to research its structure and properties.
• Suffering a phase transformation and unit cell expansion after fluorination.
• Determining chemical formula and fluorine ions occupation of fluorinated product.

Here we report using the transition metal difluoride ZnF2 to fluorinate K2NiF4-type cuprates La2−xSrxCuO4 (x = 0, 1.5, 0.3). Unlike other fluorinating agents, the technique is nontoxic, easy to handle and the byproduct ZnO can be removed. After fluorination, the fluorinated product of La2CuO4 suffers a phase transformation and unit cell expansion. While La1.85Sr0.15CuO4 and La1.7Sr0.3CuO4 indicate no change in structure after fluorination, their space groups still are I/4mmm, however, their lattices become larger, too. We emphasis the structural characterizations for fluorinated product of La1.7Sr0.3CuO4 by high-resolution transmission electron microscopy (HRTEM) images and electron diffraction (ED) patterns. Moreover, we determine the chemical formula to be La1.54Sr0.46CuO3.1F0.9 and the fluorine ions are prone to be located in the apical sites of the Cu(O, F)6 octahedron in the structure of post-treated fluorinated product of La1.7Sr0.3CuO4. Magnetization investigations demonstrate that partial replacement of the lanthanum by strontium changes the magnetism of post-treated fluorinated products of La2−xSrxCuO4 (x = 0, 0.15, 0.3) and they exhibit a paramagnetic behavior.