High temperature X-ray diffraction investigations of La2CuO4+delta

The single-phased La2CuO4+delta (delta =0.08) sample with T-c of 37K was pr epared by electrochemical oxidation. Its phase transition in the temperatur e range from 25 degreesC to 450 degreesC was studied by X-ray diffraction, TGA and other measurements. When the sample is heated to above 90 degreesC, it decomposes into two new phases (beta and epsilon) without noticeable ox ygen loss. Both beta and epsilon phases are superconductors. When temperatu re is above 200 degreesC, the new phases change into a more stable supercon ducting phase (alpha) with abrupt oxygen loss. The alpha phase gradually lo ses its oxygen when temperature increases from 200 degreesC to 450 degreesC , and finally changes into the parent compound La2CuO4.