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LAKHTIN (b), and V. A. MEZRIN (a) The YBa,Cu,O, -d-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 k T ) valence band with a hole effective mass mp = 3 to 5 free electron masses.

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It is shown that the presence of proton-associated dipole centers (OH)− can cause glass-like properties to appear at low temperatures in the oxides ABO3−y doped with cations with a lower valence. These properties are due to the splitting of the orientationally degenerate states of (OH)− dipolar centers as a result of proton tunneling and random crystal fields. It is established that deuterium or tritium substituted for hydrogen can cause unusual and anomalously large isotopic effects in the contributions of degenerate centers to the thermodynamic properties and the absorption of elastic and electromagnetic waves.

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