Dependence of the conductivity and thermoelectromotive force for YBa2Cu3-xCoxO6+delta solid solutions on the content of weakly bound oxygen

The partial enthalpy of the weakly bound oxygen and the electrical conducti vity and thermoelectromotive force (thermoemf) of the YBa2Cu3-xCoxO6+delta solid solution at x = 0, 0.2, 0.4, and 0.6 were determined as functions of the oxygen content in the temperature range 600-850 degrees C. It was found that the increased cobalt content results in an increase in the average bi nding energy of weakly bound oxygen. The enthalpy of labile oxygen was obse rved to sharply decrease when its content in the solid solution was reduced below a certain level, Based on a change in the thermoemf coefficient with the oxygen content, it was concluded that the character of electrical cond uctance changed from extrinsic to inherent. The dependence of the conductiv ity and thermoemf are interpreted within a model of an electronic structure that contains two narrow hands. It was shown that the oxygen concentration dependence of the position of the narrow p-type band correlates with that of the partial enthalpy of weakly bound oxygen. It was found that the incre ased content of cobalt in the solid solution results in an increase in the average bonding energy of labile oxygen and in a decrease of the energy of this band.