Nonstoichiometry and Phase Transition in RBa₂Cu₃O_7-δ (R: Y, Sm, Eu, Gd, Dy, Ho, Er and Yb)

Abstract

The orthorhombic (O)-to-tetragonal (T) phase transition in RBa₂Cu₃O_7-δ (R: Y, Sm, Eu, Gd, Dy, Ho, Er and Yb) was investigated by high temperature X-ray powder diffraction and thermogravimetry (TG) in air and O₂ gases. The ortho-I phase gradually transforms to the tetragonal phase through the ortho-II phase with increas-ing temperature, accompanied with increase of oxygen vacancies. No crystallographic distinction between the ortho-I and the ortho-II phase was found. The O-T transition in all systems is of second order and the transition temperature increases with increasing atomic number of R elements.