Oxygen Deficiency in YM₂Cu₃O_7+y (M=Ba, Sr) Family

Abstract

YBa 2 Cu 3 O 7+ y samples, slowly cooled after annealing, are orthorhombic and exhibit a complete transition at 90 K. On the contrary, rapidly quenched samples are tetragonal and their T c 's are 20 K lower than those of the slowly cooled ones. It is found from thermogravimetric analysis that the amount of oxygen deficiency in the tetragonal samples is greater than the orthorhombic ones. This fact indicates that the structural difference is attributed to both the disordering of oxygen vacancies and the difference in oxygen vacancy amount. In addition, YSr 2 Cu 3 O 7+ y samples are tetragonal and exhibit complete transition at 81 K.