The role of the electron-hole system in the thermodynamics of YBa2Cu3O7-δ-gas equilibrium

The YBa2Cu3O7-δ-gas equilibrium is studied theoretically in terms of the approach proposed earlier by the authors. The contribution of the electron-hole system of the HTSC oxide to the equilibrium thermodynamics is studied for several models of the electronic structure. Oxygen-oxygen interactions in the basal plane are taken into account to calculate the chemical potential of oxygen ions in the oxide, distinct from the previous paper where these interactions are disregarded. It is shown that the equilibrium is well described for a sufficiently broad (much broader than kT) valence band with a hole effective mass mp ≅ 3 to 5 free electron masses. (orig.)