THE EXCHANGE OF OXYGEN ISOTOPES IN HIGH-TEMPERATURE SUPERCONDUCTORS

The following paper presents a new method of characterizing the exchange of oxygen in oxygen-containing solids. High-temperature superconductors of Y-Ba-Cu-O systems display a unique exchange process which is determined to a great extent by stoichiometric compositions and structure. A preliminary characterization of the exchange may be stated as follows: the greater the oxygen affinity, the smaller the tendency towards isotope exchange. As the oxygen affinity decreases, the initial temperature required for diffusion and exchange processes to the site increases, the initial temperature required for diffusion and exchange processes to the site increases, and the temperature at which emission and absorption of oxygen are equal decreases. The extent of the relative accumulation of O-18 in the gas phase bears a correlation to the transition temperature in the superconducting Y-Ba-Cu-O phase. A very similar mechanism for the diffusion of oxygen in solid phases can be inferred from the alteration of the O-18 content in the O-34(2) in the gas phase. Qualitative conclusions regarding isotope exchange processes, surface conditions, and the movement of oxygen may be drawn from the time- and temperature-dependent changes in various formulated coefficients. In addition, the method presented allows opposing processes within a solid to be distinguished and recorded separately.