Low-temperature oxidation of YBa2Cu3O6.0 with nitrogen dioxide

Nitrogen dioxide was used to oxidize nonsuperconducting, powdered YBa2Cu3O6.0 to form a material that exhibits the Meissner effect at liquid nitrogen temperature. Nitrogen dioxide treatment at 200 °C for 70 h results in a mixed-phase material containing superconducting YBa2Cu3O6.9 that exhibits onset of superconductivity at 91.5 K and a midpoint at 88 K. During a 70-h exposure of YBa2Cu3O6 to NO2 at 200 °C, a mixture of oxidation and degradation products is formed, including YBa2Cu3O6.9 (61% by weight) and Ba(NO3)2 (23% by weight). Heating the NO2-treated product to 900 °C results in the evolution of NO, NO2, and O2; cooling the sample and annealing at 400 °C in an O2 stream generates the superconducting oxide.