Oxygen content and structure of Ba 2YCu 3O x below 525°C

Abstract

The relationship between the crystal structure and oxygen content was established for Ba 2YCu 3O x ceramic. Samples whose initial values of x were either 6.98 (orthorhombic structure) or 6.16 (tetragonal structure) were annealed side by side at 380 to 525°C in flowing nitrogen containing a fixed, small amount of oxygen. The powders were heated until their weightd stabilized and this required very long times at the lower temperatures. The room temperature structure and x were obtained for these samples. X-ray diffraction was also used to determine the structure of powders with intermediate x while the samples were heated using conditions which prevented any change in oxygen content. At room temperature samples with x⩽6.40 are tetragonal, those with ⩾6.42 have the orthorhombic structure, while samples with 6.42⩽ x⩽6.55 transform to tetragonal as the temperature raised. The effect of metastability, the kinetics of oxidation and temperature influence are discussed. The 25°C lattice parameters as a function of x are reported for the annealed samples.