INFLUENCE OF FLUORINE-GAS TREATMENT ON THE STRUCTURAL AND PHYSICAL-PROPERTIES OF LA2CUO4

La2 CuO4 samples have been treated under pure fluorine gas at temperatures TF2 ranging from 20 °C to 300 °C. For TF = 300 °C, the starting oxide is completely decomposed in a mixture of LaF3 and CuF2, whereas for TF ≤ 230 °C the resulting product crystallizes in an orthorhombic distortion of the K2NiF4-type structure as La2CuO4 starting oxide. After the fluorination process, the weight uptake of the material, the elemental analysis and a noticeable change of the unit cell parameters corroborate the incorporation of fluorine atoms inside the La2CuO4 lattice. These oxyfluorides are superconductors below Tc = 40 ± 1K and exhibit a metallic behaviour above Tc. On the other hand the three-dimensional antiferromagnetic ordering observed in starting oxide near TN ∼- 250 K appears to be destroyed by the fluorine-gas treatment. © 1990.