PROPERTIES OF THE TETRAGONAL SUPERCONDUCTOR CABALACU3OX

The compound CaBaLaCu3O6.9 is a tetragonal bulk superconductor with a Tc of 80 K. CaBaLaCu3Ox is isomorphic to tetragonal YBa24Cu3Ox in which the Ca and La ions are both located at the Y- and Ba-site. High temperature X-ray diffraction and thermogravimetric measurements show no indication for 'order-disorder' transitions involving the oxygen ions. TEM micrographs of CaBaLaCu3Ox show no evidence for a/b twinning. The oxygen content and the partial oxygen pressure of CaBaLaCu3Ox are determined as a function of temperature. The standard enthalpy change for the oxidation reaction, ΔH, is determined as 190.4(0.3) kJ/mol O2. Transmission electron diffraction patterns show weak but distinct half-order spots indicating an ordering which can be described by a supercell having axes twice as large as the basic unit cell.