Vacuum annealing treatment effects on structure and superconductivity in RBa 2Cu 3O 7−δ and YBa 2−xK xCu 3O 7−δ

Abstract

We report the effects of heat treatment in a very low pressure at 800°C on the structure and superconducting properties of RBa 2Cu 3O 7−δ R=Y, Nd and Eu, and YBa 2−xK xCu 3O 7−δ. These systems undergo an orthorhombic (and superconducting) to amorphous (and non superconducting) transition, caused by large oxygen losses ( δ = 1.3−1.8) and disordering of oxygen vacancies. Then by a controlled technique we restored the oxygen content to a value of δ = 0 and the orthorhombic crystal structure and superconductivity were fully recovered. The substitution of barium with potassium is reported for the first time. The recovered NdBa 2Cu 3O 7−δ ( δ = 0.7) is superconducting with T C = 89 K.