INVESTIGATION OF THE DOMINANT POINT-DEFECTS IN TETRAGONAL YBA2CU3OX AT ELEVATED-TEMPERATURES

The manner in which oxygen is incorporated into YBa2Cu3Ox (YBCO) at si milar to 800 degrees C for values of x close to 6 is shown to be in th e form of neutral oxygen interstitials, O-i(x). The experimental data on which this conclusion is based are obtained from measurements of ox ygen partial pressure, P(O-2), as a function of composition x and temp erature T (5.99 less than or equal to x less than or equal to 6.35, 82 5 less than or equal to T less than or equal to 1120K). The data are o btained by a solid-state electrochemical method. Other conclusions of this study include: (a) Or are noninteracting for x similar or equal t o 6. (b) The stoichiometric composition of YBCO is x similar or equal to 6.0. (c) The reaction enthalpy of oxidation is 179 kJ/mol O-2. (d) The Fermi level changes by similar or equal to-0.2 eV as x increases f rom 6.05 to 6.35.