Thermodynamics of the movable oxygen and conducting properties of the solid solution YBa2Cu3-xCoxO6+δ at high temperatures |
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Authors: | M V Patrakeev E B Mitberg A A Lakhtin I A Leonidov V L Kozhevnikov K R Poeppelmeier |
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Institution: | (1) Institute of Solid State Chemistry, 620219 Ekaterinburg, Russia;(2) Northwestern University, IL-60208 Evanston, USA;(3) Institute of Solid State Chemistry, 620219 Ekaterinburg, Russia |
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Abstract: | High precision coulometric measurements of the equilibrium oxygen content in the solid solution YBa2Cu3-xCoxO6+δ, where x=0, 0.2, 0.4, 0.6 and 0.8, were carried out using a double-cell technique in the temperature range 600 – 850 °C and
at oxygen pressure varying between 10−5 and 1 atm. The data were employed to determine the partial molar enthalpy and entropy of the movable oxygen depending on
δ and x. The electrical conductivity and thermopower were also measured in the same range of the external parameters, and
their dependence on the oxygen concentration was determined at different cobalt content. The data reveal several types of
oxygen sites participating in the gas-solid equilibrium. The behavior of thermodynamic functions is indicative of the partial
ordering of the complex species which form the structural layer Cu1-xCoxOδ with variable content of oxygen and cobalt. It was shown that replacement of copper by cobalt does not result in appearance
of the electronic charge carriers. The behavior of the thermopower and electric conductivity was explained with a narrow band
model. The energy change with δ and x of the p-band, which dominates the conductivity, was found to follow the respective
change in the oxygen partial enthalpy. Thus, electronic carriers in the layered structure of the cuprate are strongly influenced
by the labile oxygen ions.
Paper presented at the 5th Euroconference on Solid State Ionics, Benalmádena, Spain, Sept. 13–20, 1998. |
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