Thermodynamic and Nonstoichiometric Behavior of Promising Hi-Tc Cuprate Systems via Electromotive Force Measurements: A Short Review

Electromotive force (EMF) measurements of oxygen fugacities as a function of stoichiometry have been made on the YBa2Cu3Ox, GdBa2Cu3Ox, NdBa2Cu3Ox, and bismuth cuprate systems in the temperature range ~400°C to 750°C by means of an oxygen titration technique with an yttria-stabilized zirconia electrolyte. The shapes of the 400°C isotherms as a function of oxygen stoichiometry for the Gd and Nd cuprate systems suggest the presence of miscibility gaps at values of x that are higher than those in the YBa2Cu3Ox system. For a given oxygen stoichiometry, oxygen partial pressures above GdBa2Cu3Ox and NdBa2Cu3Ox are higher (above x = 6.5) than that for the promising YBa2Cu3Ox system.