Synthesis and superconducting properties of fluorinated La₂CuO₄ using NH₄F

Superconducting La₂CuO_4-δF_y samples were synthesized by heating La₂CuO₄ together with a fluorinating reagent, NH₄F, at 240°C in flowing oxygen gas. Bulk superconductivity with T_c = 42 K in the samples was confirmed by DC magnetic susceptibility measurements. The enhancement in the orthorhombicity of the K₂NiF₄ phase (a = 5.319 Å, b = 5.442 Å, c = 13.20 Å) was observed. The lower and upper critical fields, H_c1(0) and H_c2(0), for the La₂CuO_4-δFy were roughly determined to be 98 Oe and 600 kOe, respectively.