Differential scanning calorimetry, X-ray diffraction and thermogravimetry were used to study the effect of O diffusion upon the structure of this material. It was found that annealing in vacuum led to an irreversible and diffusion-controlled phase transformation from the superconducting orthorhombic structure to the semiconducting tetragonal perovskite structure. At low heating rates, the transition began at about 550C. With increasing heating rate, the diffusion mechanism caused a delayed onset and a broadening of the temperature regime of the transition. It was found that the interdiffusion coefficient for O at 700C was about 10-12cm2/s.

H.U.Krebs, R.Wördenweber: Journal of Applied Physics, 1988, 63[5], 1642-5