Characterization of Ba sub 2 YCu sub 3 O sub x as a function of oxygen partial pressure; Part II dependence of the O-T transition on oxygen content.

Dilatometry and high temperature x-ray powder diffraction have been used to characterize the orthorhombic (O) to tetragonal (T) transition in the 93K superconductor Ba sub 2 YCu sub 3 O sub x (7.0 > X > 6.0). The O-T transition temperature has been determined as function of oxygen partial pressure, P sub O sub 2 = 0.09, 2% air and 100% oxygen. Thermal expansion coefficients for individual lattice parameters as well as average values have been measured for the O and T structures. A volume change of ~+0.21% has been observed for transformation of O to T at 650C. The structural change occurs at X = 6.63 +- 03.