The decomposition of the oxalate precursor and the stability and reduction of the YBa₂Cu₄O₈ superconductor studied by TG coupled with FTIR and by XRD

The 124 superconductor YBa2Cu4O8 was prepared from the oxalate precursor Y2(C2O4)3. ·4BaC2O4·8CuC2O4·xH2O at one atmosphere oxygen pressure. In O2 the precursor decomposes in one step at 300°C and more gradually (300°–600°C) in Ar. The stability of the superconductor is strongly dependent on the gas atmosphere: in O2 and in air there is no significant weight change as long as the temperature does not exceed 800°C, whereas in a 1% O2-99%N2 mixture decomposition starts at about 670°C with the formation of CuO and YBa2Cu3Ox withx<7. The reduction of YBa2Cu4O8 in a 5% H2-95% Ar mixture takes place in at least four major steps with formation of products such as Y2O3, BaO, Cu2O, Cu, BaY2O4 and Ba4Y2O7.